Chapter 11: Water & Nutrients

Marijuana Horticulture: The Indoor / Outdoor Medical Grower’s Bible

by Jorge Cervantes

Water provides a medium to transport nutrients necessary for plant life and make them available for absorption by the roots. Water quality is essential for this process to work at maximum potential. The laws of physics govern plant water uptake. Applying these laws, a grower can provide precise, properly balanced components t grow outstanding marijuana indoors.

Microscopic root hairs absorb water and nutrients in oxygen present in the growing medium and carry them up the stem to the leaves. This flow of the water from the soil through the plant is called the transpiration stream. A fraction of the water is processed and used in photosynthesis. Excess water evaporates into the air, carrying waste products along with it via the stomata in the leaves. This process is called transpiration. Some of the water also returns manufactured sugars and starches to the roots.

The roots support the plants, absorb nutrients, and provide the initial pathway into the vascular system. A close-up look at a root reveals the xylem and phloem core, vascular tissue that is enveloped by a cortex tissue f the layer between the internal vascular and external epidermal tissue. The microscopic root hairs are located on the epidermal tissue cells. These tiny root hair follicles are extremely delicate and must remain moist. Root hairs must be protected from abrasions, drying out, extreme temperature fluctuations, and harsh chemical concentrations. Plant health and well-being is contingent upon strong, healthy roots.

The nutrient absorption begins at the root hairs, and the flow continues throughout the plant via the vascular system. Absorption is sustained by diffusion. In the process of diffusion, water and nutrient ions are uniformly distributed throughout the plant. The intercellular spaces – apoplasts and connecting protoplasm, symplast – are the pathways that allow the water and nutrient ins and molecules to pass thorough the epidermis and the cortex to the xylem and phloem’s vascular bundles. The xylem channels the solution through the plant while phloem tissues distribute the food manufactured by the plant. Once the nutrients are transferred to the plant cells, each cell accumulates the nutrients it requires to perform its specific function.

The solution that is transported through the vascular bundles or veins of a plant has many functions. This solution delivers nutrients and carries away the waste products. It provides pressure to help keep the plant structurally sound. The solution also cools the plant by evaporating the water via the leaves’ stomata.

Water Quality

The concentration of calcium (Ca) and magnesium (Mg) indicate how “hard” the water is. Water containing 100 to 150 milligrams of calcium (CaCO3) per liter is acceptable to grow marijuana. “Soft” water contains less than 50 milligrams of calcium per liter and should be supplemented with calcium and magnesium.

Water with high levels of chloride frequently contains high levels of sodium, but the opposite is not true. Water with high levels of sodium does not necessarily contain excessive levels of chloride (chlorine).

At low levels sodium appears to bolster yields, possibly acting as a partial substitute to compensate for potassium deficiencies. But when excessive, sodium is toxic and induces deficiencies of other nutrients, primarily potassium, calcium, and magnesium.

Chloride (chlorine) is essential to the use of oxygen during photosynthesis, and it is necessary for root and leaf cell division. Chloride is vital to increase the cellular osmotic pressure, modify the stomata regulation, and augment the plant’s tissue and moisture content. A solution concentration if less than 140 parts per million (ppm) is usually safe for marijuana, but some varieties may show sensitivity when foliage turns pale green and wilts. Excessive chlorine causes the leaf tips and margins to burn and causes the leaves to turn a bronze color.

Simple water filters do not clean dissolved solids from the water. Such filters remove only debris emulsified 9suspended) in water; releasing dissolved solids from their chemical bond is more complex. A reverse osmosis machine uses small polymer, semipermeable membranes that allow pure water to pass through and filter out the dissolved solids from the water. Reverse osmosis machines are the easiest and most efficient means to clean raw water.


The roots draw the nutrient solution up the plant by the process of osmosis. osmosis is the tendency of fluids to pass through a semipermeable membrane and mix with each other until the fluids are equally concentrated on both sides of the membrane. Semipermeable membranes located in the root hairs allow specific nutrients that are dissolved in the water to enter the plant while the other nutrients and impurities are excluded. Since salts and sugars are concentrated in the roots, the electrical conductivity (EC) inside the roots is (almost) always higher than outside the roots. Transporting the nutrients by osmosis works, because it depends on relative concentrations of each individual nutrient on each side of the membrane; it does not depend on the total dissolved solids (TDS) or EC of the solution. For nutrients to be drawn in by the roots via osmosis, the strength of the individual elements must be greater than than of the roots.

But, transport of water (instead of nutrients) across the semipermeable membrane depends on EC. For example, if the EC is greater outside the roots than inside, the plant dehydrates as the water is drawn out of the roots. In other words, salty water with a high EC can dehydrate the plants.

Reverse osmosis machines are used to separate the dissolved solids from the water. These machines move the solvent (water) through the semipermeable membrane, but the process is reversed. It moves from lower concentrations to higher. The process is accomplished by applying pressure to the tainted water to force only pure water through the membrane. The water is not totally “pure” with EC of “0”, but most of the dissolved solids are removed. The efficiency of reverse osmosis depends on the type of of membrane, and the chemical composition of the dissolved solids in the tainted water.

Unfortunately, common tap water often contains high levels of sodium (Na), calcium (Ca), alkaline salts, sulfur (S), and chlorine (Cl). The pH could also be out of the acceptable 6.5 to 7 range. Water containing sulfur is easily smelled and tasted. Saline water is a little more difficult to detect. Water in coastal areas is generally full of salt that washes inland from the ocean. Dry regions that have less than 20 inches annual rainfall also suffer from alkaline soil and water that is often packed with alkaline salts.

Table salt, sodium chloride (NaCl), is added t many household water systems. A small amount of chlorine, below 140 ppm, does not affect marijuana growth, but higher levels cause foliage chlorosis and stunt growth. Do not use salt softened water. Salty, brackish, salt-softened water is detrimental to cannabis. Chlorine also tends to acidify soil after repeated applications. The best way to get chlorine out of the water is to let it sit one or two days in an open container. the chlorine will evaporate (volatize) as a gas when it comes in contact with the air. If chlorine noticeably alters soil pH, adjust it with a commercial “pH UP” product or hydrated lime.

The metric system facilitates the measurement of “dry residue per liter”. Measure the dry residue per liter by pouring a liter of water on a tray and allowing it to evaporate. The residues of dissolved solids that remains after all the water evaporates is the “dry residue per liter”. The residue is measured in grams. Try this at home to find out the extent of impurities. Fertilizers have a difficult time penetrating root tissue when they must compete with resident dissolved solids.

Water that is loaded with high levels of dissolved solids (salts in solution) is possible to manage but requires different tactics. highly saline water that contains sodium will block the uptake of potassium, calcium, and magnesium. Salt-laden water will always cause problems. If water contains 300 ppm or less dissolved solids, allow at least 25 percent of the irrigation water to drain out of the bottom of containers with each watering. If raw water contains more than 200 ppm of dissolved solids, use a reverse osmosis device to purify the water. Add nutrients to pure water as a way to avoid many nutrient problems.

Dissolved salts, caused by saline water and fertilizer, quickly build up toxic levels in container gardens. Excessive salts inhibit seed germination, burn the root hairs and tips or edges of leaves, and stunt the plant. Flush excess salt buildup from growing mediums by applying two gallons of water per gallon of medium and repeat leaching using a mild pH-corrected fertilizer solution. Leach growing medium every two to four weeks, if using soft water r saline water. hard water and well water in dry climates are often alkaline, and usually contain contain notable amounts of calcium and magnesium. Cannabis uses large quantities of both nutrients, but too much calcium and magnesium can build up in soil. in general, water that tastes good to people also tastes good to cannabis.


large plants use more water than small plants, but there are many more variables than size that dictate a plant’s water consumption. The age f the plant, container size, soil texture, temperature, humidity, and ventilation all contribute to water needs. Change any of these variables, and the water consumption will change. Good ventilation is essential to promote a free flow of fluids, transpiration, and rapid growth. The healthier a plant, the faster it grows and the more water it needs.

Small plants with a small root system in small containers must be watered often. Water frequently – as soon as the soil surface dries out. Water frequently – as soon as the soil surface dries out. if exposed to wind, the small plants will dry out very quickly.

irrigate soil and soilless mixes when they are dry one-half inch below the surface. As long as the drainage is god, it is difficult to overwater fast-growing cannabis. Four week old clones flowering in 2 to 3 gallon containers need to be irrigated one or twice daily. in fact, most growers prefer smaller containers because they are easier to control.

irrigate larger plants in the vegetative and flowering stages when soil is dry one half inch below the surface. Flowering marijuana uses high levels of water to carry on rapid floral formation. Withholding the water stunts the flower formation.

Plants that are exposed to wind dry out much faster. outdoor, terrace, and patio plants will use up to three or four times more water on a hot, windy day. Keeping up with the watering is difficult and time consuming. Use an automated watering system or break the wind to lessen its impact on the plants. Mulch will also lessen the evaporation from the soil.

use plenty of water, and allow up to 10 percent runoff during each watering. The runoff will prevent the fertilizer from building up in the soil. Water early in the day, so excess water will evaporate from the soil surface and leaves. Leaving the foliage and the soil wet overnight invites a fungal attack.

Moisture meters take most of the guesswork out of irrigating. They can be purchased for less than $30 and are well worth the money. The meter measures exactly how much water the soil contains at any level or point. often the soil will not hold the water evenly, and it develops dry pockets. Checking the moisture with a finger provides an educated guess but disturbs the root system. A moisture meter will give an exact moisture reading without disturbing the roots.

Cultivate the soil surface to allow the water to penetrate evenly and guard against dry soil pockets. it also keeps the water from running down the crack between the inside of the pot and the soil and out the drain holes. Gently break up and cultivate the top half inch of the soil with your fingers or a salad fork. be careful not to disturb the tiny surface roots.

After you develop some skill at knowing when the plants need water, you can check to see how heavy they are simply by tipping them. Once you get the hang of it, all you will have to do is tip each container.

it is easier to keep pots in straight lines when growing and watering, and it is much easier to keep track of watered pots when they are in straight line.

Overwatering is a common problem, especially with small plants. Too much water drowns the roots by cutting off their supply of oxygen. If you have symptoms of overwatering, buy a moisture meter! It will let both you and your garden breathe easier. Sometimes, parts of the soil are overwatered and other soil pockets remain boney dry. Cultivating the soil surface, allowing even water penetration, and using a moisture meter will overcome this problem. one of the main causes of overwatering is poor air ventilation! The plants need to transpire water into the air. If there is nowhere for this wet, humid air to go, gallons of water are locked in the grow room air. Well ventilated air carries the moist air away, replacing it with fresh, dry air. If using trays t catch runoff water, use a turkey baster, large cyringe, or sponge to draw the excess water from the tray. Signs of overwatering are: leaves curled down, and slow growth. Symptoms of overwatering are often subtle, and inexperienced gardeners may not see any blatant symptoms for a long time.

marijuana does not like soggy soil. Soil kept too wet drowns the roots, squeezing out oxygen. this causes slow growth and possible fungal attack. Poor drainage is most often the cause of soggy soil. It is compounded by poor ventilation and high humidity.

Underwatering is less of a problem; however, it is fairly common if small (1-2 gallon) pots are used and the grower does not realize the water needs of rapid growing plants. Small containers dry out quickly and may require daily watering. if forgotten, water starved plants become stunted. Once tender root hairs dry out, they die. Most growers panic when they see their prize-marijuana plants wilt in bone dry soil. Dry soil, even in pockets, makes root hairs dry up and die. it seems t take forever for the roots to grow new root hairs and resume rapid growth.

Add a few drops (one drop per pint) of a biodegradable, concentrated liquid soap like Castille or Ivory to the water. it will act as a wetting agent by helping the water penetrate the soil more efficiently, and it will guard against dry soil pockets. Most soluble fertilizers contain a wetting agent. Apply about one quarter to one half as much water / fertilizer as the plant is expected to need, and then wait 10-15 minutes for it to totally soak in. Apply more water.fertilizer until the soil is evenly moist. If trays are underneath the pots, let excess water remain in the trays a few hours or even overnight before removing it with a large turkey baster.

Another way to thoroughly wet pots is to soak the containers in water. This is easy to do with small pots. Simply fill a 5-gallon bucket with 3 gallons of water. Submerge the smaller pt inside the larger pot, for a minute or longer, until the growing medium is completely saturated. Wetting plants thoroughly insures against dry soil pockets.

having a readily accessible water source is very convenient, and it saves time and labor. A 4×4 foot garden containing 16 healthy plants in 3 gallon pots needs 10 to 25 gallons of water per week. Water weighs eight pounds a gallon. That’s a lot of containers to fill, lift, and spill. Carrying water in containers from the bathroom sink to the garden is okay when plants are small, but when they are large, it is a big, sloppy, regular job. Running a hose int the garden saves much labor and mess. A lightweight, half inch hose is easy to handle and is less likely to damage the plants. If the water source has ht and cold water running out of the same tap, and it is equipped with threads, attach a hose and irrigate with tepid water. Use a dishwasher coupling if the faucet has no threads. the hose should have an on/off valve at the outlet, so water flow can be controlled while watering. A rigid water wand will save many broken branches while leaning over to water in tight quarters. Buy a water wand at the nursery or construct one from plastic pvc pipe. Do not leave water under pressure in the hose for more than a few minutes. garden hoses are designed to transport water, not hold it under pressure, which may cause it t rupture.

To make a siphon or gravity-fed system, place a barrel, at least fur feet high, in the grow room. Make sure it has a lid to reduce the evaporation and the humidity. If the grow room is too small for the barrel, move it to another room. The attic is a good place because it promotes good pressure. Place a siphon hose on the top of the tank, or install a pvc on/off valve near the bottom of the barrel. It is easy t walk off and let the barrel overflow. An inexpensive device that measures the gallons of water added to the barrel is available at most hardware stores. You can also install a float valve in the barrel to meter out the water and retain a constant supply.

Drip systems deliver nutrient solution one drop at a time or in a low volume, via a low pressure plastic pipe with friction fittings. Water flows down the pipe and out the emitter one drop at a time or at a very slow rate. The emitters that are attached to the main hose are either spaghetti tubes or a nozzle dripper actually emitting from the main hose. Drip irrigation kits are available at garden stores and building centers. You can also construct your own drip system from component parts.

Drip systems offer several advantages. Once setup, drip systems lower watering maintenance. Fertilizer may also be injected into the irrigation system (fertigation); naturally, this facilitates fertilization but gives the same amount of water and nutrient to each plant. If setting up a drip system, make sure the growing medium drains freely to prevent soggy soil or salt buildup. if you are growing clones that are all the same age and size a drip system would work very well. However, if you are growing many different varieties of plants, they may need different fertilizer regimens.

i interviewed several growers that loved the convenience and constant feeding-ability of their drip systems. All the growers irrigated (fertigated) with mild nutrient solution. They mixed the nutrient solution in a reservoir and pumped it through plastic feeder hoses. They also grew clones in smaller containers and kept root growth to a minimum by keeping the nutrients and the water in constant supply.

A drip system attached to a timer disperses nutrient solution at regular intervals. If using such as system, check the soil for water application daily. Check several pots daily t ensure they are watered evenly and that all the soil gets wet. Drip systems are very convenient and indispensable when you have to be away for a few days. however, do not leave a drip system on its own for me than four consecutive days, or you could return to a surprise!

Drip systems cost a few dollars to set up, but with the consistency they add to a garden, their expense is often paid ff by a bountiful yield. be careful! Such an automated system could promote negligence. Remember that gardens need daily care. If everything is automated, the garden still needs monitoring. All the vital signs: moisture, pH, ventilation, humidity, etc, still need to be checked and adjusted daily. Automation, when applied properly, adds consistency, uniformity, and usually a higher yield.

One indoor grower I met was out of town for five consecutive days every week. he watered and fertilized his plants in a tray with 2 inch tall sides and watered the plants from above until the tray was full of water. he left for five days, and the plants needed no watering while he was gone. he used regular potting soil and added about 10 percent perlite. His plants needed maintenance when he returned, but the plants grew quite well.

Misdiagnosed Disorders

many indoor garden problems, and to lesser degree outdoor problems, are misdiagnosed as a lack of fertilizer. Often, disease and insects cause such problems. other times, problems are caused by an imbalanced pH of the growing medium and water. a pH between 6.5 and 7.0 in soil and 5.8 to 6.5 in hydroponics will allow nutrients become less available. For example, a full point movement in pH represent a tenfold increase in either alkalinity or acidity. This means that a pH of 5.5 would be ten times more acidic than a pH of 6.5. in soil, a pH below 6.5 may cause a deficiency in calcium, which causes root tips to burn and leaves to get fungal infections and dead spots on foliage. A pH over 7 could slow down the plant’s iron intake and result in chlorotic leaves causing veins to yellow.

Incorrect pH contributes to most serious nutrient disorders in organic soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH is critical to the livelihood of these activities. When the pH fluctuates in a hydroponic garden, the nutrients are still available in the solution for uptake, and the pH is not as critical. Electrical conductivity is the most critical indicator of plant health and nutrient uptake in hydroponics.

Once a plant shows symptoms, it has already undergone severe nutritional stress. It will take time for the plant to resume vigorous growth. Correct identification of each symptom as soon as it occurs is essential to help plants retain vigor. Indoor, greenhouse, and some outdoor marijuana crops are harvested so fast that plants do not have time to recover from nutrient imbalances. One small imbalance could cost a week of growth. That could be more than 10 percent of the plant’s life!

Do not confuse nutrient deficiencies or toxicities with insect and disease damage r poor cultural practices.

The temperature within the leaves can climb to an excess f 110F. It happens easily because the leaves store the heat radiated by the lamp. At 100F, the internal chemistry of a marijuana leaf is disturbed. The manufactured proteins are broken down and become unavailable to the plant. As the internal temperature of the leaves climbs, they are forced to use and evaporate more water. About 70 percent of the plant’s energy is used in this process.

The basic elements of the environment must be checked and maintained at specific levels to avoid problems. Check each of the vital signs – air, light, soil, water, temperature, humidity, etc. – and fine-tune the environment, especially ventilation, before deciding that plants are nutrient deficient.

Nutrient deficiencies are less common when using fresh potting soil fortified with micronutrients. If the soil or water supply is acidic, add dolomite lime to buffer the soil pH and to keep it sweet. Avoid nutrient problems by using fresh planting mix, clean water, and a complete nutrient solution. Maintain the EC and pH at proper levels, and flush the system with mild nutrient solution every four weeks.


Nutrients are elements that the plant needs to live. Carbon, hydrogen, and oxygen are absorbed from the air and water. the rest of the elements, called nutrients, are absorbed from the growing medium and nutrient solution. Supplemental nutrients supplied in the form of a fertilizer allow marijuana to reach its maximum potential. nutrients are grouped into three categories: macronutrients or primary nutrients, secondary nutrients, and micronutrients or trace elements. Each nutrient in the above categories ca further classified as either mobile or immobile.

Mobile nutrients – nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and zinc (Zn) – are able to translocate, move from one portion of the plant to another as needed. For example, nitrogen accumulated in older leaves translocates to younger leaves to solve a deficiency. The result, deficiency symptoms appear on the older, lower leaves first.

Immobile nutrients – calcium (Ca), boron (B), chlorine (Cl), cobalt (C), copper (Cu), iron (Fe), manganese (Mn), molybendum (Mo), silicon (Si) and sulfur (S) – do not translocate to new growing areas as needed. They remain deposited in their original place in older leaves. This is the reason deficiency symptoms appear first in the upper, new leaves on top of the plant.

Mobile nutrients translocate within a plant. They move to the specific part of the plant where they are needed; this causes the older leaves to show deficiencies first.


Nitrogen (N) – mobile

Marijuana loves nitrogen and requires high levels of it during vegetative growth but lower levels during the balance of life. Nitrogen is easily washed away and must be replaced regularly, especially during vegetative growth. Excess levels of nitrogen in harvested plants cause the dried marijuana to burn poorly.

Nitrogen regulates the cannabis plant’s ability to make proteins essential for new protoplasm in the cells. Electrically charged nitrogen allows the plant to tie proteins, hormones, chlorophyll, vitamins, and enzymes together. Nitrogen is essential for the production of amino acids, enzymes, nucleic acids, and chlorophyll and alkaloids. This important nutrient is mainly responsible. For leaf and stem growth, as well as overall size and vigor. Nitrogen is most active in young buds, shoots, and leaves. Ammonium (NH4+) is the most readily available form of nitrogen. Be careful when using too much of this form; it can burn the plants. Nitrate (NO3-) – the nitrate form of nitrogen – is much slower to assimilate than ammonium. Hydroponic fertilizers use this slower acting nitrogen compound and mix it with ammonium.

Nitrogen is the most common nutrient deficiency. The symptoms include slow growth. Lower leaves cannot produce chlorophyll and become yellow between the veins while the veins remain green. Yellowing progresses through the entire leaf, eventually causing it to die and drop off. Stems and leaves’ undersides may turn reddish purple, but this can also be a sign of a phosphorus deficiency. Nitrogen is very mobile, and it dissipates into the environment quickly. It must be added regularly to sustain fast growing gardens.

Treat deficiency by fertilizing with N or a complete N-P-K fertilizer. You should see results in four to five days. Fast acting organic sources of nitrogen include seabird guano, fish emulsion, and blood meal. Growers also report excellent results by adding bio-fertilizers to stimulate the uptake of nitrogen.

An overdose of nitrogen will cause excessively lush foliage that is soft and susceptible to stress, including insect and fungal attacks. The stems become weak and they may fold over very easily. The vascular transport tissue breaks down, and water uptake is restricted. In severe cases, leaves turn a brownish-copper color, dry, and fall off. Roots develop slowly, and they tend t darken and rot. Flowers are smaller and sparse. Ammonium toxicity is most common in acidic soils, while nitrate toxicity is more prevalent in alkaline soil.

Treat toxicity by flushing the growing medium of the affected plants with a very mild, complete fertilizer. Severe problems require that more water be flushed through the growing medium to carry away the toxic elements. Flush a minimum of three times the volume of water for the volume of the growing medium. Do not add more fertilizer tat contains nitrogen for one week so the excess nitrogen in foliage can be used. If the plants remain excessively green, cut back n the nitrogen dose.

Phosphorus (P) – mobile

Cannabis uses the highest levels of phosphorus during germination, seedling, cloning, and flowering. Super Bloom fertilizers, designed for flowering, have high levels of phosphorus.

Phosphorus is necessary for photosynthesis and provides a mechanism for the energy to transfer within the plant. Phosphorus – one of the components of DNA, many being enzymes and proteins – is associated with overall vigor, resin, and seed production. The highest concentrations of phosphorus are found in root growing tips, growing shoots, and vascular tissue.

A lack of phosphorus causes stunted growth and smaller leaves; leaves turn bluish-green and blotches often appear. Stems, leaf stems (petioles), and main veins turn reddish-purple starting on the the leaf’s underside. The reddening of the stems and the veins is not always well pronounced. The leaf tips of older leaves turn dark and curl downward. Severely affected leaves develop large purplish black necrotic (dead) blotches. These leaves later become bronzish-purple, dry, shrivel up, contort, and drop off. Flowering is often delayed, buds are uniformly smaller, seed yield is poor, and plants become very vulnerable to fungal and insect attack. Phosphorus deficiencies are aggravated by clay, acidic, and soggy soils. Zinc is also necessary for proper utilization of phosphorus.

Deficiencies are somewhat common and are often misdiagnosed. Deficiencies are most common when the growing medium pH is above 7 and phosphorus is unable to be absorbed properly; the soil is acidic (below 5.8) and / or there is an excess of iron and zinc; the soil has become fixated (chemically bound) with phosphates.

Treat deficiency by lowering the pH to 5.5-6.2 in hydroponic units; 6 to 7 for clay soils; and 5.5-6.5 for potting soils so phosphorus will become available. If the soil is too acidic, and an excess of iron and zinc exists, phosphorus becomes unavailable. If you are growing in soil, mix a complete fertilizer that contains phosphorus into the growing medium before planting. Fertigate with an inorganic, complete hydroponic fertilizer that contains phosphorus. Mix in the organic nutrients – to add phosphorus to soil. Always sue finely ground organic components that are readily available to the plants.

Toxic signs of phosphorus may take several weeks to surface, especially if excesses are buffered by a stable pH. Marijuana uses a lot of phosphorus throughout its life cycle, and many varieties tolerate high levels. Excessive phosphorus interferes with calcium, copper, iron, magnesium, and zinc stability and uptake. Toxic symptoms of phosphorus manifest as a deficiency of zinc, iron, magnesium, calcium, and copper; zinc is the most common.

Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Severe problems require more water to be flushed through the growing medium. Flush a minimum of three times the volume of water for the volume of the growing medium.

Potassium (K) – mobile

Potassium is used at all stages of growth. Soils with a high levels of potassium increase a plant’s resistance to bacteria and mold.

Potassium helps combine sugars, starches, and carbohydrates, which is essential to their production and movement. It also is essential to growth by cell division. It increases the chlorophyll in the foliage and helps regulate the stomata openings so plants make better use of the light and air. Potassium is essential in the accumulation and translocation of carbohydrates. It is necessary to make the proteins that augment the oil content and improve the flavor in cannabis plants. It also encourages strong root growth and is associated with disease resistance and water intake. The potash form of potassium oxide is (K2O).

Potassium-starved plants initially appear healthy. Deficient plants are susceptible to disease. Symptoms include the following: older leaves (first tips and margins, followed by whole leaves) develop spots, turn dark yellow, and die. Stems often become weak and sometimes brittle. Potassium is usually present in the soil, but it is locked in by high salinity. First, leach the toxic salt out of the soil and then apply a complete N-P-K fertilizer. Potassium deficiency causes the internal temperature of the foliage to climb and the protein cells to burn or degrade. Evaporation is normally highest on leaf edges, and that’s where the burning takes place.

Treat deficiency of potassium by fertilizing with a complete N-P-K fertilizer. Occasionally, a grower will add potassium directly to the nutrient solution. Organic growers add potassium in the form of soluble potash ()wood ashes) mixed with water. Be careful when using wood ash, the pH is normally above 10. Use a pH lowering mix to bring the pH to around 6.5 before application. Foliar feeding to cure potassium deficiency is not recommended.

Toxicity occurs occasionally and is difficult to diagnose because it is mixed with the deficiency symptoms of other nutrients. Too much potassium impairs and slows the absorption of magnesium, manganese, and sometimes zinc and iron. Look for signs of toxic potassium buildup when symptoms of magnesium, manganese, zinc, and iron deficiencies appear.

Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Severe problems require that more water be flushed through the growing medium. Flush with a minimum of three times the volume of water for the volume of the growing medium.

Secondary Nutrients

The secondary nutrients – magnesium, calcium, and sulfur – are also used by the plants in large amounts. Rapid-growing indoor marijuana crops are able to process more secondary nutrients than most general-purpose fertilizers are able to supply. Many growers opt to use high quality two and three part hydroponic fertilizers to supply all necessary secondary and trace elements. but be careful, these three nutrients may be present in high levels in the ground water. it is important to consider these values when adding nutrient supplements. If growing in the soil or soilless mix with a pH below 7 such as Peat-Lite, incorporating one cup of fine (flour) dolomite lime per gallon of medium ensures adequate supplies of calcium and magnesium.

Macronutrients are the elements that the plants use most. The fertilizers usually show nitrogen (N), potassium (P), phosphorus (K) as (N-P-K) percentages in big numbers on the front of the package. They are always listed in the same N-P-K order. These nutrients must always be in an available form to supply marijuana with the building blocks for rapid growth.

Magnesium (Mg) – mobile

Marijuana uses a lot of magnesium, and deficiencies are common, especially in acidic (pH below 7) soils. Adding dolomite lime to acidic potting soils before planting will stabilize the pH, plus it will add magnesium and calcium to the soil. Add Epsom salts with each watering to correct magnesium deficiencies, if no dolomite was added when planting. Use Epsom salts designed specifically for plants rather than the supermarket type.

Magnesium is found as a central atom in every chlorophyll molecule, and it is essential to the absorption of light energy. It aids in the utilization of nutrients. Magnesium helps enzymes make carbohydrates and sugars that are later transformed into flowers. It also neutralizes the soil acids and toxic compounds produced by the plant.

Magnesium deficiency is common indoors. The lower leaves, and later the middle leaves, develop yellow patches between dark, green veins. Rusty brown spots appear on the leaf margins, tips, and between the veins, as the deficiency progresses. The brownish leaf tips usually curl upward before dying. The entire plant could discolor in a few weeks, and if severe, turn a yellow-whitish tinge before browning and dying. A minor deficiency will cause little to no problem with growth. however, minor deficiencies escalate and cause a diminished harvest as flowering progresses. Most often, magnesium is in the soil if there is an excess of potassium, ammonia (nitrogen), and calcium (carbonate). Small root systems are also unable to take in enough magnesium to supply heavy demand. A high EC slows the water evaporation and will also diminish magnesium availability.

Treat deficiency by watering with two teaspoons of Epsom salts (magnesium sulfate) per gallon of water. For fast results, spray the foliage with a 2 percent solution of Epson salts. If the deficiency progresses to the top of the plant, turning lower leaves progressively more green. Continue regular watering schedule with Epsom salts until the symptoms totally disappear. Adding Epsom salts regularly is not necessary when the fertilizer contains available magnesium. Use a foliar spray of Epsom salts for a fast cure. Another options to apply magnesium sulfate monohydrate in place of Epsom salts. Add fine dolomite lime to soil and soilless mix to add a consistent supply of both calcium and magnesium over the long term. Always use the finest dolomite available.

Control the room and root-zone temperatures, humidity, pH and EC of the nutrient solution, pH, and EC of the nutrient solution at 70 to 75F. keep ambient air temperature at 75F day and 65F night. Use a complete fertilizer with an adequate amount of magnesium. Keep the soil pH above 6.5, the hydroponic pH above 5.5, and reduce high EC for a week.

The extra magnesium in the soil is generally not harmful, but it can inhibit calcium uptake. Signs of excess magnesium are described below.

Magnesium toxicity is rare and difficult to discern with the naked eye. If extremely toxic, the magnesium develops a conflict with other fertilizer ions, usually calcium, especially in hydroponic nutrient solutions. The toxic buildup of magnesium in soil that is able to grow marijuana is uncommon.

Calcium (Ca) – immobile

Cannabis requires nearly as much calcium as other macronutrients. Avert deficiencies in the soil and in most soilless mixes by adding fine dolomite lime r using soluble-hydroponic fertilizers containing adequate calcium.

Calcium is fundamental to cell manufacturing and growth. Calcium is necessary to preserve membrane permeability and cell integrity, which ensures proper flow of nitrogen and sugars. it stimulates enzymes that help build strong cell and root walls. Cannabis must have some calcium at the growing tip of each root.

Deficiency of calcium is somewhat uncommon indoors, but not uncommon in fiber hemp. Frequently, plants can process more calcium than is available. it also washes out of the leaves that are sprayed with water. Deficiency signs may be difficult to detect. They start with weak stems, very dark green foliage, and exceptionally slow growth. Young leaves are affected, and they show the signs first. Severe calcium deficiency causes new, growing shoots to develop yellowish to purple hues and to disfigure before shriveling up and dying; bud development is inhibited, the plants are stunted, and harvest is diminished. Growing tips could show signs of calcium deficiency if the humidity is maxed out. At 100 percent humidity, the stomata close, which stops the transpiration to protect the plant. The calcium that is transported by transpiration becomes immobile.

Treat deficiencies by dissolving one-half teaspoon of hydrated lime per gallon of water. Water the deficient plants with calcium-dosed water as long as the symptoms persist. Or use a complete hydroponic nutrient that contains adequate calcium. Keep the pH of the growing medium stable.

Toxicity is difficult to see in the foliage. It causes wilting. Toxic levels also exacerbate deficiencies of potassium, magnesium, manganese, and iron. The nutrients become unavailable, even though they are present. if excessive amounts of soluble calcium are applied early in life, it can also stunt growth. If growing hydroponically, an excess of calcium will precipitate with sulfur in the solution, which causes the nutrient solution to suspend in the water and to aggregate into clumps causing the water to become cloudy (flocculate). Once the calcium and sulfur combine, they form a residue (gypsym Ca(SO4) 2(H2O) ) that settles to the bottom of the reservoir.

Sulfur (S) – immobile

many fertilizers contain some form of sulfur, and for this reason, sulfur is seldom deficient. Growers avoid elemental (pure) sulfur in favor of sulfur compounds such as magnesium sulfate. The nutrients combined with sulfur mix better in water.

Sulfur is an essential building block of many hormones and vitamins, including vitamin B1. Sulfur is also an indispensable element in many plant cells and seeds. The sulfate form of sulfur buffers the water pH. Virtually all ground, river, and lake water contains sulfate. Sulfate is involved in protein synthesis and is part of the amino acid, cystine, and thiamine, which are building blocks of proteins. Sulfur is essential in the formation of oils and favors, as well as for respiration and the synthesis and breakdown of fatty acids. Hydroponic fertilizers separate sulfur from calcium in an “A” container and a “B” container. If combined in a concentrated form, sulfur and calcium will form crude, insoluble gypsym (calcium sulfate) and settle as residue to the bottom of the tank.

Young leaves turn lime green to yellowish. As shortage progresses, leaves yellow interveinally and lack succulence. Veins remain green, and leaf stems and petioles turn purple. Leaf tips can burn, darken, and hook downward. According to literature, youngest leaves should yellow first. But Mauk from Canna Coco in the Netherlands, who has conducted detailed scientific experiments with nutrients, says, “We have repeatedly noticed that the symptoms were most obvious in the older leaves.” Sulfur deficiency resembles a nitrogen deficiency. Acute sulfur deficiency causes elongated stems that become woody at the base.

Sulfur deficiency occurs indoors when the pH is too high or when there is excessive calcium present and available.

Acute deficiency causes more and more leaves to develop purple leaf stems and yellow leaves.

Treat deficiency by fertilizing with a hydroponic fertilizer that contains sulfur. Lower pH to 5.5 to 6. Add inorganic sulfur to a fertilizer that contains magnesium sulfate (Epsom salts). Organic sources of sulfur include mushroom composts and most animal manures. Make sure to apply only well-rotted manures to avoid burning the roots.

An excess of sulfur in the soil causes no problems if the EC is relatively low. At a high EC, the plants tend to take up more available sulfur which blocks uptake of other nutrients. Excess sulfur symptoms include overall smaller, dark green foliage. Leaf tips and margins could discolor and burn when severe.

Treat toxicity by flushing the growing medium of affected plants with a very mild and complete fertilizer. Check the pH of the drainage solution. Correct the input pH to 6. Severe problems require more water to be flushed through the growing medium. Flush a minimum of three times the volume of water for the volume of the growing medium.


Micronutrients, also called trace elements or trace nutrients, are essential to chlorophyll formation and must be present in minute amounts. They function mainly as catalyst to the plant’s process and utilization of other elements. For best results, and to ensure a complete range f trace elements is available, use fertilizers designed for hydroponics. High quality hydroponic fertilizers use food-grade ingredients that are completely soluble and leave no residues. If using an inexpensive fertilizer tat does not list specific analysis for each trace element on the label, it’s a good idea to add soluble trace elements in a chelated form. Chelated micronutrients are available in powdered and liquid form. Add and thoroughly mix micornutrients into the growing medium before planting. Micronutrients are are often impregnated in commercial potting sis and soilless mixes. Check the ingredients n the bag to ensure that the trace elements were added to the mix. Trace elements are necessary in minute amounts but can easily reach toxic levels. Always follow the manufacturer’s instructions to the letter when applying micronutrients, because they are easy to over-apply.

Zinc (Zn) – mobile

Zinc is the most common micronutrient found deficient in arid climates and alkaline soils.

Zinc works with manganese and magnesium to promote the same enzyme functions. Zinc cooperates with other elements to help form chlorophyll as well as prevent its demise. It is an essential catalyst for most plants’ enzymes and auxins, and it is crucial for stem growth. Zinc play a vital part in sugar and protein production. It is fairly common to find zinc-deficient cannabis. Deficiencies are most common in soils with a pH f 7 or more.

Zinc is the most common micronutrient found deficient. First, younger leaves exhibit interveinal chlorosis, and new leaves and growing tips develop small, thin blades that contort and wrinkle. The leaf tips, and later the margins, discolor and burn. Burned spots on the leaves could grow progressively larger. These symptoms are often confused with a lack of manganese or iron, but when zinc deficiency is severe, new leaf blades contort and dry out. Flower buds also contort into odd shapes, turn crispy dry, and are often hard. A lack of zinc stunts all new growth including buds.

Treat zinc-deficient plants by flushing the growing medium with a diluted mix of a complete fertilizer containing chelated trace elements, including zinc, iron, and manganese. Or add a quality-brand hydroponic micronutrient mix containing cheated trace elements.

Zinc is extremely toxic in excess. Severely toxic plants die quickly. Excess zinc interferes with the iron’s ability to function properly and causes an iron deficiency.

Manganese (Mn) – immobile

Manganese deficiency is relatively common indoors.

manganese is engaged in the oxidation-reduction process associated with the photosynthetic electron transport. This element activates many enzymes and plays a fundamental part in the chloroplast membrane system. manganese assists nitrogen utilization along with iron in chlorophyll production.

Young leaves show symptoms first. They become yellow between veins (interveinal chlorosis), and the veins remain green. Symptoms spread from younger to older leaves as the deficiency progresses. Necrotic 9dead) spots develop on severely affected leaves which become pale and fall off; overall plant growth is stunted, and maturation may be prolonged. Severe deficiency looks like a severe lack of magnesium.

To treat the deficiency, lower the pH, leach the soil, and add a complete, chelated micronutrient formula.

Young and newer growth develop chlorotic, dark orange to dark, rusty brown mottling on the leaves. Tissue damage shows on young leaves before progressing to the older leaves. Growth is slower, and overall vigor is lost. Toxicity is compounded by low humidity. The additional transpiration causes more manganese to be drawn into the foliage. A low pH can cause toxic intake of manganese. An excess of manganese causes a deficiency of iron and zinc.

Iron (Fe) – immobile

iron is available in a soluble chelated form that is immediately available for absorption by the roots. Deficiency indoors is common in alkaline soils.

Iron is fundamental to the enzyme systems and to transport electrons during photosynthesis, respiration, and chlorophyll production. Iron permits plants to use the energy provided by sugar. A catalyst for chlorophyll production, iron is necessary for nitrate and sulfate reduction and assimilation. Iron colors the earth from brown to red, according to concentration. Plants have a difficult time absorbing iron. Acidic soils normally contain adequate iron for cannabis growth.

Iron deficiencies are common when the pH is above 6.5 and uncommon when the pH is below 6.5. Symptoms may appear during rapid growth or stressful times and disappear by themselves. Young leaves are unable to draw iron from older leaves, even though it is present in the soil,. The first symptoms appear on the smaller leaves as veins remain green and areas between the veins turn yellow. Interveinal chlorosis starts at the opposite end of the leaf tip: the apex of the leaves attached by the petiole. Leaf edges can turn upward as the deficiency progresses. Leaves fall off in severe cases. Iron deficiency is sometimes traced to an excess of copper.

Treat deficiency by lowering the soil pH to 6.5 or less. Avoid fertilizers that contain excessive amounts of manganese, zinc, and copper, which inhibit iron uptake. High levels of phosphorus compete with the uptake of iron. Improve the drainage; excessively wet soil holds little oxygen to spur iron uptake. Damaged or rotten roots also lower iron uptake. Increase root zone temperature. Apply chelated iron in liquid form to root zone. Chelates are decomposed by light and must be thoroughly mixed with the growing medium to be effective. Exposing the nutrient solution to light causes depleted iron. Sterilizing the nutrient solution with UV light causes iron to precipitate. Leaves should green up in four to five days. Complete, balanced, hydroponic nutrients contain iron, and deficiencies are seldom a problem. Organic sources of iron, as well as chelates, include cow, horse, and chicken manure. Use only well-rotted manures to avoid burning plants.

Excess of iron is rare. High levels of iron do not damage cannabis, but it can interfere with phosphorus uptake. An excess of iron causes the leaves to turn bronze accompanied by small, dark brown leaf spots. If iron chelate is over applied, it will kill the plant in a few days. Treat excess iron by leching plants heavily.

The following group of micronutrients is seldom found deficient. Avoid deficiencies by using a high-quality hydroponic fertilizer that contains chelated micronutrients.

Boron (B) – immobile

Usually causes no problems, but boron must be available during the entire life of a pant.

Boron deficiencies seldom occurs indoors. Boron is still somewhat of a biochemical mystery. We know that boron helps with calcium uptake and numerous plant functions. Scientists have collected evidence to suggest boron helps with synthesis, a base for the formation of the nucleic acid (RNA uracil). Strong evidence also supports boron’s role in cell division, differentiation, maturation, and respiration as well as a link to pollen germination.

Stem tip and root tip grow abnormally. Root tips often swell, discolor, and stop elongating. Growing shoots look burned and may be confused with a burn from being too close to the HID light. First leaves thicken and become brittle, top shoots contort and/or turn dark, which is later followed by progressively lower-growing shoots. When severe, growing tips die, and leaf margins discolor and die back in places. Necrotic spots develop between leaf veins. Root steles (insides) often become mushy – perfect hosts for rot and disease. Deficient leaves become thick, distorted, and wilted with chlorotic and necrotic spotting.

Treat boron-deficient plants with one teaspoon of boric acid per gallon of water. You can apply this solution as a soil drench to be taken up by the roots, or apply hydroponic micronutrients containing boron. Hydroponic gardeners should keep boron dosage below 20 parts per million (ppm), because boron quickly becomes toxic if it is concentrated in the solution.

Leaf tips yellow first, and as the toxic conditions progress, leaf margins become necrotic toward the center of the leaf. After the leaves yellow, they fall off. Avoid using excessive amounts of boric acid-based insecticides.

Chlorine (Chloride) (Cl) – immobile

Chloride is found in many municipal water systems. Cannabis tolerates low levels of chlorine. It is usually not a component of fertilizers and is almost never deficient in gardens that grow cannabis.

Chlorine, in the form of chloride, is fundamental to photosynthesis and cell division in the roots and the foliage. It also increases osmotic pressure in the cells, which open and close the stomata to regulate moisture flow within the plant tissue.

It is uncommon to be deficient. Young leaves pale and wilt, and roots become stubby. As the deficiency progresses, leaves become chlorotic and develop a characteristic bronze color. The rots develop thick tips and become stunted.

Treat deficiency by adding chlorinated water.

Young leaves develop burned leaf tips and margins. Very young seedlings and clones are the most susceptible to damage. Later, the symptoms progress throughout the plant. Characteristic yellowish-bronze leaves are smaller and slower to develop.

Let heavily chlorinated water sit out overnight, stirring occasionally. Chlorine will volatize and disappear into the atmosphere. Use this water t mix the nutrient solution or to irrigate the garden.

Cobalt (Co) – immobile

This nutrient is seldom mentioned as necessary for plant growth, and most fertilizer labels do not include cobalt. Cobalt is virtually never deficient in indoor cannabis gardens.

Cobalt is necessary for countless beneficial bacteria to grow and flourish. It is also vital for nitrogen absorption. Scientific evidence suggests this element is linked to enzymes needed to form aromatic compounds. When deficient, the problems with nitrogen availability occur.

Copper (Cu) – immobile

Copper is concentrated in the roots. It is also used as a fungicide.

Copper is a component of numerous enzymes and proteins. necessary in minute amounts, copper helps with carbohydrate metabolism, nitrogen fixation, and the process of oxygen reduction. it also helps with the making of proteins and sugars.

Copper deficiencies are not rare. Young leaves and growing shoots wilt, leaf tips and margins develop necrosis and turn a dark, copper-gray. Occasionally, an entire copper-deficient plant wilts, drooping even when adequately watered. Growth is slow and the yield decreases. A small deficiency can cause new shoots to die back.

Apply a copper based fungicide such as copper sulfate. Do not apply if the temperature is above 75F to avoid burning the foliage. Apply a complete hydroponic nutrient that contains copper. Cannabis plants seldom develop a copper deficiency.

Copper, although essential, is extremely toxic to the plant even in minor excess. Toxic levels slow to overall plant growth. As the toxic level climbs, symptoms include interveinal iron chlorosis (deficiency) and stunted growth. Fewer branches grow, and the roots become dark, thick, and slow growing. Toxic conditions accelerate quickly in acidic soils. Hydroponic gardeners must carefully monitor their solution to avoid copper excess.

treat toxicity by flushing the soil or the growing medium to help expel the excess copper. Do not use copper-based fungicides.

Molybdenum (Mb) – immobile

Molybdenum is seldom deficient. It is part of two major enzyme systems that convert nitrate to ammonium. This essential element is used by cannabis in very small quantities. It is most active in roots and seeds.

This micronutrient is almost never found deficient in cannabis. Deficiency promotes nitrogen shortage. First, the older and middle-aged leaves yellow, and some develop interveinal chlorosis; then the leaves continue to yellow and develop cupped or rolled up margins as the deficiency progresses. Acute symptoms cause the leaves to become severely twisted, die, and drop. Overall growth is stunted. Deficiencies are worst in acidic soils.

Excess is uncommon in marijuana gardens. An excess of molybdenum causes a deficiency of copper and iron.

Silicon (Si)

Silicon is readily available in most soils, water, and as far as I know, it does not cause cannabis any complications due to deficiencies or excesses.

Silicon is absorbed by the plants as silicic acid. Silicon assists in keeping iron and manganese levels consistent. It is found mainly in the epidermal cell walls where it collects in the form of hydrated amorphous silica. It also accumulates in the walls of other cells. Adequate and soluble silicon guarantees stronger cell walls that resist pest attacks and increase heat and drought tolerance.

A lack of silicon has been proven t decrease yields of some fruits and cause new leaves to deform.

Pests and diseases have a difficult time penetrating the plants that are sprayed with a silicon-based repellent / insecticide.

Nickel (Ni)

Enzymes require nickel to break down and use the nitrogen from the urea. It is also essential to iron absorption. Seldom deficient and subtly mixed with other nutrient deficiencies, most commonly nitrogen.

Sodium (Na)

This is one of the problem elements. A little bit will go a long way! Sodium is taken up by the roots very quickly and in small amounts (50 ppm). It can block enough other nutrients causing severe deficiencies to result. When mixed with chlorine, it turns into table salt, which is the worst possible salt to put on the plants. Be very careful to measure your input water to ensure that it contains less than 50 ppm sodium. The less sodium in the solution, the better.

Fluoride (F)

Some water systems are abundant with fluoride. If concentrated, fluoride can become toxic. I have yet to see fluoride toxicity or deficiency cause problems in an indoor grow room.


The goal of fertilizing is to supply the plants with the proper amount of nutrients for vigorous growth, without creating toxic conditions by overfertilizing. A 2-gallon container full of rich, fertile potting soil will supply all the necessary nutrients for the first month of growth, but the development might be slow. After the rots have absorbed most of the available nutrients, more must be added to sustain vigorous growth. Unless fortified, soilless mixes require fertilization from the start. I like to start fertilizing fortified soilless mixes after the first week or two of growth. Most commercial soilless mixes are fortified with trace elements.

Marijuana’s metabolism changes as it grows and so do its fertilizer needs. During germination and seedling growth, intake of phosphorus is high. The vegetative growth stage requires larger amounts of nitrogen for green leaf growth, and phosphorus and potassium are also necessary in substantial levels. During this leafy and vegetative growth stage, use a general purpose or a grow fertilizer with high nitrogen content. In the flowering stage, nitrogen takes a backseat to potassium, phosphorus, and calcium intake. Using a super bloom fertilizer with less nitrogen and more potassium, phosphorus, and calcium promotes fat, heavy, dense buds. Cannabis needs some nitrogen during flowering, but very little. With no nitrogen, buds do not develop to their full potential.

Now we come to the confusing part about the guaranteed analysis of commercial fertilizer mixes. Federal and state laws require nutrient concentrations to appear prominently on the face of the fertilizer packages, even though the accuracy of the values is dubious.

Do you think the N-P-K numbers on the label give the percentages of nitrogen, phosphorus, and potassium? Well, yes and no. The scale measures nutrients with different scales. Nitrogen is listed as total combined elemental. Most hydroponic fertilizers break nitrogen into slow-acting nitrate (NO3) and ammonium (NH4). Phosphoric anhydride (p2O5) is listed as the form of phosphorus, but this figure understates phosphorus content by 44 percent. It gets worse! The balance (56 percent) of the phosphorus molecule is comprised of oxygen. Twenty percent P2O5 is 8.8 percent actual phosphorus. potassium (K) is listed in the potash form of potassium oxide (k2O) of which 83 percent of the stated value is actually elemental potassium.

The rest of the mineral nutrients are listed in their elemental form that represents the actual content. Most often, the mineral elements used in the fertilizer formulas are listed in chemical compounds on the label. Look at the fertilizer labels to ensure that the elements, especially trace elements, are chelated and readily available for root absorption. Also, be careful about having too much sodium in your water / nutrient solution. The sodium will block potassium and several other nutrients, causing deficiencies and slow growth.

Nutrients in the United States are measured in parts-per-million (ppm_), even though they are expressed as a percentage concentration on the label. The ppm scale is simple and finite – almost. The basics are simple: one part per million in one part of 1,000,000, so divide by one million to find parts per million,. To convert percentages into ppm, multiply by 10,000 and move the decimal four (4) spaces to the right.

Fertilizers are either water-soluble or partially soluble (gradual-release). Both soluble and gradual release fertilizers can be organic or chemical.

Chemical Fertilizers

The diversity of hydroponic fertilizers is amazing. Local shop owners know which ones work best in the local climate and water. local store owners know a lot about the local water and the growers’ needs. They are in a perfect position to develop their own nutrient solution or adapt one that works well with their water. A few manufacturers do not do their homework and make bad nutrients. Most manufacturers are conscious and manufacture excellent fertilizers. As always, read the entire fertilizer label and follow the directions.

Soluble-chemical fertilizers are an excellent choice for indoor container cultivation. Soluble fertilizers dissolve in water and are easy to control, and they can be easily added or washed (leached) out of the growing medium. Control the exacting amounts of nutrients available to the plants in an available form with water-soluble fertilizers. The soluble fertilizer may be applied in a water solution onto the soil. In general, high quality hydroponic fertilizers that use completely soluble food grade nutrients are the best value. Avoid low quality fertilizers that do not list all necessary micronutrients on the label.

Chemical granular fertilizers work well but can easily be over applied, creating toxic soil. They are almost impossible to leach out fast enough to save the plant.

Osmocote chemical fertilizers are time release and are used by many nurseries because they are easy to apply and only require one application every few months. Using this type of fertilizer may be convenient, but exacting control is lost. They are best suited for ornamental, containerized plants where labor costs and uniform growth are the main concerns.

Organic Fertilizers

Organically grown cannabis has a sweeter taste, but implementing an organic indoor garden requires horticultural know-how. The limited soil, space, and the necessity for sanitation must be considered when growing organically. Outdoors, organic gardening is easy because all of the forces of nature are there for you to seek out and harness. Indoors, few of the natural phenomena are free and easy. Remember, you are Mother Nature and must create everything! The nature of growing indoors does not lend itself to long-term organic gardens, but some organic techniques have been practiced with amazing success.

Most indoor organic gardens use potting soil high in worm castings, peat, sand, manure, leaf mold, compost, and fine dolomite lime. In a container, there is little space to build the soil by mixing all kinds of neat composts and organic nutrients to cook down. Even if it were possible to build the soil in a container, it would take months of valuable growing time and it could foster bad insects, fungi, etc. it is easier and safer to throw old, depleted soil outdoors, and start new plants with fresh organic soil.

Organic nutrients, manure, worm castings, blood and bone meal, etc, all work very well to increase the soil nutrient content, but nutrients are released and available at different rates. The nutrient availability may be tricky to calculate, but it is somewhat difficult to over apply organic fertilizers. Organic nutrients seem to be more consistently available when used in combination with one another. usually, growers use a mix of about 20 percent worm castings with other organic agents to get a strong, readily available nitrogen base. They fertilize with bat guano, the organic super bloom, during flowering.

An indoor garden using raised beds allows true organic methods. The raised beds have enough soil to hold the nutrients, promote organic activity, and when managed properly, ensure a constant supply of nutrients. The raised beds must have enough soil mass to promote heat and fundamental organic activity.

Outdoor organic gardens are easy to implement and maintain. Using compost tea, manures, bulky compost, and other big, smelly things is much easier outdoors.

Organic Teas

Compost teas not only contain soluble organic nutrients diluted in water, but they support a potent elixir tat is loaded with beneficial microbes that fight ff pests and diseases. For example, a quarter teaspoon of a well-made compost tea holds more than a billion bacteria and at least 15 feet of fungi strands! A good compost tea also contains thousands of different species of protozoa, nematodes, and mycorrhizal fungi.

Disease-causing organisms are unable to complete with beneficial bacteria and fungi. beneficial bacteria also work to break down plant residues and toxic materials, plus they improve soil structure and water holding ability.

The best teas are made from well-rotted compost, because it contains a complex collection of microbes and nutrients. Just make sure the compost pile has heated to 135F for at least 3 days to ensure it is free of most diseases. You can usually buy quality compost at the local nursery. If using manure, make sure it has been well decomposed.

You can brew the tea in a 5-gallon bucket. Add about a gallon of rotted compost of manure to 4 gallons of water. Stir well, and let the mix sit for several days. You can also put sifted compost into a nylon stocking, and submerge it in the bucket. To stir, simply bounce the stocking around in the water. Stir the mixture gently several times a day to integrate oxygen and remove microbes from the compost. Adequate oxygen keeps the brew fresh. If it starts to smell foul, anaerobic bacteria are present. Add fresh water and stir more often. The good aerobic bacteria re-establish as soon as they have an ample supply of oxygen.

Dilute the tea at the rate of 1 to 5 with water. Add more water to the same bucket, and continue to brew 3 to 4 more batches before starting a new batch.

make super tea by gently agitating and oxygenating the soup. This will supercharge the tea and add 10 to 100 times more microbes than regular compost tea.

Mixing Fertilizers

Always read the entire label, and follow the directions. To mix, dissolve the powder and the crystals into a little warm water, and maker sure it is totally dissolved before adding the balance of the tepid water. This will ensure that the fertilizer and the water mix evenly. Liquid fertilizers can be mixed directly with water.

Containers have very little growing medium in which to hold the nutrients, and toxic salt buildup may become a problem. Follow dosage instructions to the letter. Adding too much fertilizer will not make the plants grow faster. it could change the chemical balance of the soil, supply too much of a nutrient, or lock in other nutrients making them unavailable to the plant.

Fertilizer Application

Some varieties can take high doses of nutrients, and other strains grow best with a minimum of supplemental fertilizer.

Determine if the plants need to be fertilized: make a visual inspection, take an N-P-K soil test, or experiment on test plants. No matter which method is used, remember, plants in small containers use available nutrients quickly and need frequent fertilizing, while plants in large planters have more soil, supply more nutrients, and can go longer between fertilizing.

Visual inspection – if the plants are growing well and have deep green, healthy leaves, they are probably getting all the necessary nutrients. The moment growth slows or the leaves begin to turn pale green, it is time to fertilize. Do not confuse yellow leaves caused by a lack of light with yellow leaves caused by a nutrient deficiency.

Taking an N-P-K soil test will reveal exactly how much of each major nutrient is available to the plant. The test kits mix a soil sample with a chemical. After the soil settles, a color reading is taken from he liquid and matched to a color chart. The appropriate percent f fertilizer is then added. This method is exact but more trouble than it is worth.

Experimenting on two or three test plants is the best way to gain experience and develop horticultural skills. Clones are perfect for this type of experiment. Give the test plants some fertilizer, and see if they green up and grow faster. You should notice a change within three to four days. If it is good for one, it should be good for all.

Now, it has been determined that the plants need fertilizer. How much? The answer is simple. Mix the fertilizer as per the instructions and water as normal, or dilute the fertilizer and apply it more often. Many liquid fertilizers are very diluted already. Consider using more concentrated fertilizers whenever possible. Remember, small plants use much less fertilizer than large ones. Fertilize early in the day, so plants have all day to absorb and process fertilizer.

It is difficult to explain how often to apply all fertilizers in a few sentences. We know that large plants use more nutrients than small plants. The more often the fertilizer is applied, the less concentrated it should be. Frequency of fertilization and dosage are two of the most widely disagreed upon subjects among growers. Indoor containerized marijuana can be pushed to incredible lengths. Some strains will absorb amazing amounts of fertilizer and grow well. Lots of growers add as much as tablespoon per gallon of Peters (20-20-20) with each watering. This works best with growing mediums that drain readily and are easy to leach. Other growers use only rich, organic potting soil. No supplemental fertilizer is applied until a super bloom formula is needed for flowering.

Fertilizing plants in the ground is much easier than fertilizing containerized plants. In the soil outdoors, roots can find many nutrients, and fertilization is not as critical. There are several ways to apply chemical fertilizer. You can top-dress a garden bed by applying the fertilizer evenly over the entire area. You can side-dress plants by applying the fertilizer around the bases of the plants. You can foliar feed plants by spraying a liquid fertilizer solution on the foliage. The method you choose will depend upon the kind of fertilizer, the needs of the plants, and the convenience of a chosen method.

When using synthetic fertilizers, it is extremely important to read the label carefully, and follow the directions. The initials “WSN” and “WIN” that you may see on the label stand for water-soluble nitrogen and water-insoluble nitrogen. WSN dissolves readily, and it is considered a fast-release nitrogen source.

Use a siphon applicator – found at most nurseries – to mix soluble fertilizers with water. The applicator is simply attached to the faucet with the siphon submerged in the concentrated fertilizer solution with the hose attached to the other end. Often, applicators are set at a ratio of 1 to 15. This means that for every 1 unit of liquid concentrate fertilizer, 15 units of water will be mixed with it. Sufficient water flow is necessary for the suction to work properly. Misting nozzles restrict this flow. When the water is turned on, the fertilizer is siphoned into the system and flow out of the hose. The fertilizer is generally applied with each watering, since a small percentage of fertilizer is metered in.

A garbage can with a garden hose fitting attached at the bottom that is set 3-4 feet off the floor will act as a gravity-flow source for the fertilizer solution. The container is filled with water and fertilizer.

When it comes to fertilization, experience with specific varieties and growing systems will tell growers more than anything else. There are hundreds of N-P-K mixes, and they all work! When choosing a fertilizer, make sure to read the entire label, and know what a fertilizer claims it can do. Do not be afraid to ask the retail clerk questions or to contact the manufacturer with questions.

Once you have an idea of how often to fertilize, put the garden on a regular feeding schedule. A schedule usually works very well, but it must be combined with a vigilant, caring eye that looks for over fertilization and signs of nutrient deficiency.

Leach soil with 1-2 gallons of mild nutrient solution per gallon of soil every month. This is the best form of preventive maintenance against toxic salt buildup in the soil.

Foliar Feeding

Foliar feeding means to spray the nutrients or bio-stimulants onto the foliage to augment available nutrients, vitamins, hormones, etc. Timing is key to achieving the best coverage and absorption.

The waxy (cuticle) surface coating (cystolith hairs and resin) on cannabis foliage makes them very poor water absorbers. This barrier wards off pest and disease attacks, but it also slows the penetration of sprays.

Young leaves are more permeable than older leaves. Nutrients and additives penetrate immature leaves faster than tougher, older leaves, and they are easier to damage with strong sprays.

Foliar feed the cannabis plants only when specific deficiency symptoms manifest. Foliar feeding is a quick fix only and is easy to overdo. High levels of nutrients in the foliage stop the roots from taking in more; this is confusing to the plant. Foliar sprays can accumulate and build up in the foliage. Never spray more than once every 10 days, and keep the spray concentration to less than 500 ppm or with an EC of less than 1.0.


Smart growers use a surfactant, surface-active substance (adjuvant), which enhances the effectiveness of foliar fertilization.

Spreaders (wetting agents) reduce the surface tension of sprays and keep them from beading up and rolling off foliage. Big, bulbous drops n the leaves mean you need to use a spreader. Flat drops that slide off the foliage mean there is too much spreader. There are nonionic, antionic, and cationic spreaders. The nonionic spreaders that do not ionize in water are the most common, and they do not react with most pesticides. Antionic and cationic spreaders are not used often.

Stickers help the spray adhere to the leaf after spraying, so it does not wash off when it rains or when dew forms. Stickers not only increase adhesion, they slow evaporation, and impart a waterproof coating. Some stickers are spreaders, too. Spreader-stickers allow the stomata on the leaves to be penetrated.

Extender (stabilizing agents) protects applied sprays against the UV radiation and heat that degrade the sprays.

Liquid and powder soaps and detergents act as surfactants, too. But, they are not nearly as effective as horticultural surfactants. Biodegradable surfactants disappear the fastest. Silicone surfactants are also mild insecticides that work to impair pest functions.

Foliar spray concentration is cumulative. Nutrients delivered via the foliage can cause a buildup of salts in and around the leaves. This is similar to the way the salts accumulate in the soil.

Over fertilizing can become one of the biggest problems for indoor growers. Too much fertilizer causes a buildup of the nutrients (salts) to toxic levels, and it changes the soil chemistry. When over fertilized, growth is rapid and lush until the toxic levels are reached. At this point, things become complicated.

Chance of over fertilization is greater in a small amount of soil that can hold only a small amount of nutrients. A large pot or planter can safely hold much more soil and nutrients, but it will take longer to flush if overdone. It is very easy to add too much fertilizer to a small container. Large containers have good nutrient holding ability.

To treat severely overfertilized plants, leach the soil with two gallons of diluted nutrient solution per gallon of soil to wash out all excess nutrients. The plant should start new growth and look better in one week. If the problem is severe and the leaves are curled, the soil may need to be leached several times. After the plant appears to have leveled off to normal growth, apply the diluted fertilizer solution.


Numerous additives or growth supplements have hit the market over the last few years. Generally, additives contain a cocktail of some of the elements listed below. Most of the additives came from the greenhouse industry or were developed for organic growers. Many of these additives do what they say they will do and work quickly; however, when growing s short eight to ten week crop, some of these additives do not have time to work properly if added near the end of the flowering cycle.

Abscisic acid (ABA)

Abscisic acid is a naturally occurring hormone that assists plants in adapting to environmental stresses like drought or cold temperatures. During winter, ABA converts leaves into stiff bud scales which cover the meristem, protecting it from cold damage or dehydration. In case of an early spring, ABA will also prolong dormancy, preventing premature sprouts which could be damaged by frost.

used in the garden, ABA may help plants resist drought and unreasonable conditions and improve productivity, strength, and performance.

Ascorbic acid (Vitamin C)

Vitamin C is thought to build tighter, heavier buds and act as an antioxidant. it is often combined with fructose, molasses, or sugar and added to the nutrient solution during the last two weeks before harvest. However, some botanists believe that although vitamin C is very important in fighting the free radical byproducts of photosynthesis, plants make their own vitamin C and are unlikely to recognize any benefit from its addition to the nutrient mix.


Salicylic acid is a naturally occurring plant hormone associated with the Willow. It is effective in preventing pathogens by speeding up the natural “systemic acquired resistance (SAR)” thereby reducing the need for pesticides. Salicylic acid (SA) will block abscisic acid (ABA) allowing the plant to return to normal after a period of stress – something to consider if ABA is being used to strengthen plants.

Aspirin can be used as a spray, a soak, or added to compost and rooting compounds. A 1:10,000 solution used as a spray will stimulate the SAR response, and the effects will last weeks to months. “Willow water” also makes a popular rooting bath.


Auxins represent a group of plant hormones that regulate growth and phototropism. They are associated with elongation of plant cells causing the branches to grow vertically while inhibiting lateral buds. “Pinching off” branch tips will reduce the auxin level and encourage bushy lateral growth as well as inducing new root formation.

Synthetic auxins are more stable and last longer than the natural solutions. They can be used as an herbicide against broadleaf weeds like dandelions, but are most often used to encourage root growth and promote flowering.


Bacteria such as mycorrhizal fungi and rhizo-bacteria are extremely beneficial in organic gardening. The presence of these organisms in the growing medium produces stronger, healthier plants that require less chemical intervention.

Actino-Iron is a commercial soil additive that contains the Streptomyces lydicus microbe. Applied to the soil, the bacterium grows around the rot system, protecting it from harmful pathogens while producing anti-fungals. Actino-Iron also contains fulvic acid and iron which feed the plant. For perennials, the effect last one growing season. For annuals, the life of the plant.

B-9 folic acid

There is little literature on the effects of B-9 on plants. It appears to serve in energy transfer within the plant and inhibits the enzyme that makes gibberellic acid resulting in a bushier dwarf-type plant without pruning. B-9 can be applied as a spray or as a soil drench.


Cellulase is a group of enzymes that act in the root zone to break down organic material which may rot and cause disease. Dead materials are converted into glucose and returned to the substrate to be absorbed by the plant. It can be used in water gardens to clean up organic sludge.


Colchicine, an alkaloid, is prepared from the dried corns and seeds of Colchicum autumnale, the autumn crocus that also produces saffron. the pale yellow powder is water soluble.

Colchicine is a very dangerous, poisonous compound that can be used to induce polyploid mutations in cannabis. Clandestine breeders started polyploid strains with colchicines, but none of the strains showed any outstanding characteristics, and cannabinoid levels were unaffected.

Rather than explain how t use colchicine, I will advise not to use it. It is very toxic and produces no charge in potency. I do not know any seed breeders that use it today.


Cytokinins are plant hormones derivative of the purine adenine, the most common cytokinin being Zeatin. They are synthesized in the roots promoting cell division, chloroplast development, leaf development, and leaf senescence. As an additive, cytokinins are most often derived from the Seaweed Ascophyllum nodosum.

Added to the soil or sprayed on the plants, cytokinins hep the plant make more efficient use of existing nutrients and water even in drought conditions. The result is a healthier plant and increased crop. Care must be given to application of cytokinins along with other plant hormones. Many commercial formulas contain a hormone cocktail which includes hormones like auxins and cytokinins that work against one another.


Enzymes are biological protein catalysts that were first crystallized and isolated in 1926. Enzymes accelerate the rates of reactions but do not change themselves as a result of this action. Enzymes are added to fertilizers and growth additives to accelerate biological activity and speed nutrient uptake by the roots.

Most enzymatic reactions happen within a temperature range of 85-105F and each enzyme has an optimal range of pH for activity. Most enzymes react with only a small group of chemical compounds that are closely related. More than 1500 different enzymes have been identified. Enzymes are grouped into six main classes and many subclasses.

Ethylene gas

Ethylene gas is a growth regulator hormone that activates the aging and ripening of flowers as well as preventing the development of buds and retarding plant growth. it is most often used by vegetable growers who force ripening of produce heading to the market. In gardening, it may be used to trigger flowering in plants.

Flower saver plus

Flower Saver Plus is a commercial product that contains the Mycorrhizae fungus which enters into a symbolic relationship with the plant by attaching itself to the root system. Mycorrhizal threads enter into root tissue then grow out into the substrate reaching more water and nutrients than the plant could find on its own. In return, the Mycorrhizae receive a protected environment and the sugars they need to thrive.

use of Mycorrhizae improves root depth, speeds maturation, and helps create resistance to drought and disease. Larger more robust root systems also improve the soil structure promoting better air and water movement.

Flower Saver Plus should be used at planting time either as a root bath or worked into the top two to four inches of soil. Look for a product that has at least 50 to 100 spores per square foot.

Seek medical attention if ingested. Avoid breathing the dust or spray, and keep out of reach of children.

Fulvic acid

Fulvic acid is a naturally occurring organic substance resulting from the microbial action on decomposing plants. Absorbed into a plant, fulvic acid will remain in the tissues and serve as a powerful antioxidant as well as providing nutrients and acting as a bio-stimulant. Fulvic acid is an excellent source of nutrition for Mycorrhizae. Growers can create fulvic acid by composting or purchase the product from a retailer. It is available in forms suitable for hydroponics or soil mediums.


Gibberellic Acid (GA) is a natural plant growth hormone which acts with auxins to break dormancy, stimulate seed germination, and grow long stems. Gibberellic Acid can be purchased as a commercial product like Mega-grow and is used to extend the grow season and force larger blooms. For best effect, use GA in complement with fertilizer and mixed into the water supply. Results can be seen in as little as a few weeks.

According to the Material Safety Data Sheet (MSDS), GA is very hazardous to humans, and I do not advise using it; however, the retail advertisements claim the product is safe.

Humic acid

Humic acids are carbons formed by the decomposition of organic substances, primarily that f vegetation. Applied to substrate, it encourages the creation of strong tissue growth and helps in nutrient transport. Plants grow thicker foliage and are more resistant to drought and disease.

Poor soils can be improved by humic acid which enhances the water holding capability an aeration in sandy soils and frees up nutrients bound in clay. It can be used as a root dip or sprayed directly onto the soil.

Humic acids are extracted from humic substances found in soil. Colors range from yellow (fulvic acid) to brown (humic acid) and black (humin).

Fulvic acid is the fraction of humic substances that is water soluble under all pH conditions. Fulvic acid stays in solution after humic acid dissipates due to acidification. Humin is the fraction of the soil organic matter that is not dissolved when the soil is treated with dilute alkali.

Hydrogen peroxide

Hydrogen peroxide (H2O2) is similar to water but carries an extra, unstable, oxygen molecule which can break down into a reactive atom and either attach itself to another oxygen atom or attack an organic molecule.

Used in horticulture, hydrogen peroxide provides a host of benefits by cleansing water of harmful substances such as spores, dead organic material, and disease-causing organisms while preventing new infections from occurring. It removes the methane and organic sulfates often found in well water as well as removing chlorine from tap water.

Hydrogen peroxide is especially useful in hydroponics, where overwatering can be a problem. it prevents oxygen depletion in the water around the rots, leading to better root growth. A solution of hydrogen peroxide can be used to sterilize seeds resulting in better germination rates.

Hydrogen peroxide is dangerous at high concentrations (35%) and will damage skin, clothing, and most anything it contacts. Lower concentrations like those found at the drug store (3%) will still need to be diluted before use, though they are not as toxic to the gardener.

Indole 3 butyric acid (IBA)

Indole 3 butyric acid is one of the auxin growth hormones. It is most often used as an effective rooting hormone. Application of IBA helps generate roots, build a larger root mass, and improve plant growth and yield.

Many commercial formulas are available in the form of water soluble salts. Cuttings can be dipped or immersed before planting. Roots can be dipped or sprayed or the soil drenched during transplanting. Once established, plants should be treated at three to five week intervals during the growing season. After harvest, IBA can be used to encourage regeneration of flowers.

IBA is hazardous to humans and animals. It can cause moderate eye injury and is harmful if inhaled or absorbed through the skin.

Isopentyl adenine (IPA)

Isopentyl adenine is a naturally occurring cytokinin which is synthetically manufactured as benzylaminopurine (BAP) for use in commercial bio-stimulants such as Rush Foliar XCell Veg and Xcell Bloom.

Xcell Veg acts in the growth stage of the plant by improving the transport of nutrients. Glycine betaine in the solution provides a barrier to environmental stress. The product is used as part of an established feeding program. It can be sprayed on, just before turning off the lights, or used as a soak in the growing medium.

Xcell Bloom also has anti-stress properties and improves nutrient transport. It stimulates flowering, reduces plant growth time, and increases cell division and lateral root growth. Flowers are larger, heavier, and have enhanced color. Both products can be used in hydroponic or soil mediums.


Rhizobium is the name given to a group of bacteria which infect the roots of legumes and create nodules that act in symbiosis with the plant. Rhizobia are host-specific and will not work with all crops. With the proper host, however, Rhizobia improve nitrogen fixation while simultaneously providing an additional source of nitrogen.

Rhizobium is most effective when added to irrigation, but it can be added to a drip or directly to the soil. Benefits will depend on proper crop / Rhizobium match. Re-innoculation is recommended every three to five years.


Spray-N-Grow is a brand name vitamin and nutrient solution that includes barium and zinc. It is sprayed on plants to provide micronutrients through the foliage, a technique said to be more effective than rot nutrition. Plants will grow faster, bloom earlier and more prolifically, have larger roots, and have a higher vitamin, mineral, and sugar content.

Because it is absorbed through the leaves, Spray-N-Grow works quickly, in as little as seven to thirty days. Tender plants will realize benefits faster than woody plants. Spray-N-Grow can be used in any type of growing medium as a complement to the established feeding regimen. It is non-chemical and safe for people and pets.


Molasses, honey, and other sugars are said to increase soil microbials, enhance regrowth, and make the pant’s use of nitrogen more effective. Molasses will raise the energy level of the plant and acts as a mild natural fungicide. Molasses is the “secret ingredient” in many organic fertilizers.

Trichoderma (002/003)

Trichoderma are fungi that colonize in the root zone, crowding out negative fungi and microorganisms while stimulating root development and resistance to environmental stress. The result is a more vibrant, stronger plant.

Canna was the first company in the indoor grow industry to sell a commercial product as a growth promoter which contains Trichoderma fungi. Colorado State University studies indicate that Promot Plus, a product containing Trichoderma, is effective in suppressing pathogenic fungi that cause rot in the seeds, roots, and stems.

The product can be applied to seeds, used during transplanting, mixed with liquid fertilizer or via drip irrigation and / or watered in. Canna’s Trichoderma contains living organisms that will reproduce after application, so a small amount will do a lot. It is nontoxic and environmentally safe.


Zeatin is one of the cytokinin growth hormones. Upon germination, zeatin moves from the endosperm to the root tip where it stimulates mitosis.

Marijuana Horticulture

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