Irrigation

Marijuana Horticulture

by Jorge Cervantes

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. 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 into 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 hot 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.