Chapter 2: Seeds and Seedlings

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

by Jorge Cervantes

Cannabis Strains

Technically and legally, all cannabis, whether rope or dope, is classified as Cannabis sativa. Regardless of origin, all cannabis is considered Cannabis sativa (C. sativa) under international law. However, according to Hemp Diseases and Pests, Dr. J.M. McPartland, R.C. Clarke, and D.P. Watson, CAB International, Cannabis sativa can be further classified as: Cannabis sativa (= C. sativa var. sativa), Cannabis indica (= C. sativa var. indica), Cannabis ruderalis (= C. sativa var. spondanea), Cannabis afghanica (= C. sativa var afghanica). Each has distinct growth patterns, look, smell, taste, etc.

Cannabis Sativa

Cannabis sativa (= C. sativa var. sativa), originated predominately in Asia, the Americas, and Africa. Each area of rigin has specific characteristics, but all have the following general traits: tall, leggy stature with spacious internodal length, a large sprawling root system, large narrow-bladed leaves, and somewhat sparse flowers when grown indoors under lights. Sativas bloom several weeks to months later than indica strains. While good producers outdoors, often growing to 15 feet or more, indoor pure sativa strains often grow too tall too fast – some up to ten feet in three months – to be practical for grow room cultivation. An HID bulb is unable to efficiently illuminate tall plants, and the yield-per-watt-of-light or yield-per-square-foot-of-space is very low. Mexican, Columbian, Thai, and Jamaican strains can be very potent, with a high THC to CBD ratio that produces a soaring, energetic, “speedy” high. But potency can also be minimal, with low levels of THC. Most exported Columbian, Mexican, Thai, and Jamaican marijuana is poorly treated throughout life and abused when dried and packed. This abuse causes more rapid degradation of THC. Consequently, seeds from fair smoke are often more potent than the parent.

Central African sativas, including the THC-potent ‘Congolese’, grow similarly to Columbian strains, with a tall leggy stature, often growing more than 15 feet tall with loosely packed buds.

South Africa has major seaports. Sailors brought Cannabis sativa from many different places and planted it in South Africa. Consequently, potency of South African weed can be very high or very low, and can grow short, tall, leggy, bushy, etc. The famous Durban Poison yields potent, pale green, early buds and is the best-known South African strain.

Asian sativas, including Thai, Vietnamese, Laotian, Cambodian, and Nepalese, have diverse growth characteristics and vary significantly in potency. While Thai and other sativas from the area are often super THC-potent, they are some of the most difficult to grow indoors and the slowest to mature. Thai strains produce very light, wispy buds after flowering for about four months on plants with large, sprawling branches. Thai, Vietnamese, Cambodian, and Laotian sativas are more prone t grow into hermaphroditic adults.

Nepalese sativas can grow oversized leaves and tall leggy plants that produce sparse, late-blooming buds, but other strains from this region develop into short, compact plants that bloom earlier. Tetrahydrocannabinol (THC) production and potency is often quite high, but can also be second-rate.

Hemp strains are all considered to be Cannabis sativa. Hemp, affectionately referred to as “rope”, is Cannabis sativa grown for fiber content. Hemp is often seeded and contains very, very low levels of THC.

Cannabis Indica

Cananbis indica (= C. sativa var. indica) originated in Pakistan and India. Indica is prized by indoor growers and breeders for its squat, bushy growth; condensed root system; stout stems; broad eaves; and dense, THC-laden, fat heavy flowers. Foliage is very dark green, and in some strains, leaves around buds turn reddish to purple. Shirt, whitish pistils turn reddish to purplish in hue. A few indicas from this part of the world have narrower leaves, long white pistils, and pale green foliage. Indica strains generally contain a higher ratio of CBD to THC which causes an effect often described as a heavy, incapacitating “sit-on-your-head” stone. Potency of the high ranges from fair to stupefying. Some indicas have a distinctive odor similar to that of a skunk or cat urine, while others smell sweet and exotic. Heavily resin-laden plants tend to be the most fungus and pest resistant. Few indicas with heavy, dense, compact buds are resistant t gray (bud) mold.

Cannabis Ruderalis

Cannabis ruderalis (= C. sativa var. spondanea) was first brought to Amsterdam from Central Europe in the early 1980s by the Seed Bank to enhance their breeding program. Very similar, if not the same “ruderalis” plants grow from Minnesota north through Manitoba and Saskatchewan, Canada. C. ruderalis is a short, weedy, scrubby plant containing very, very little THC, but it starts the flowering cycle after a few weeks of growth. Photoperiod does not include flowering in C. ruderalis. Sometimes confused with more potent indicas, pure C. ruderalis is true ditch weed. It yields a headache rather than a high. Today a few breeders have incorporated the early flowering C. ruderalis genes with other early blooming C. sativa, C. indica, and C. afghanica.

Cannabis Afghanica

Cannabis afghanica (= C. sativa var. afghanica) originated near present day Afghanistan. It is quite short, seldom reaching six feet, with distinctive, broad, dark green leaflets and leaves. Dense branching and short internodes, most often with long leaf stems (petioles), dominate the profile of C. afghanica. The most common examples of pure C. afghanica include the many different hash plants and Afghani strains. C. afghanica is cultivated exclusively for drugs with much of the resin being made into hashish. It is known for the high cannabinoid content. Many growers and breeders do not distinguish C. afghanica from C. indica, lumping them both into the C. indica category.


Explosive growth of the seed breeders and legal seed sales in the Netherlands, the United Kingdom, Canada, France, Switzerland, Spain, etc, has given way to more strains of cannabis than ever before. Most popular strains of cannabis are a combination of two or more of the following: C. sativa, C. indica, C. ruderalis, and C. afghanica. But there are also many seeds with the genes from just one of the above. These strains of cannabis are bred to grow best indoors. Others grow best in greenhouses, and still others outdoors in specific climates.

A seed contains all the genetic characteristics of a plant. Seeds are the result of sexual propagation and contain genes from each parent, male and female. Some pants, known as hermaphrodites, bear both male and female flowers on the same plant. The genes within a seed dictate a pant’s size; disease and pest resistance; root, stem, leaf, and flower production; cannabinoid levels; and many other traits. The genetic makeup of a seed is the single most important factor dictating how well a plant will grow under artificial light or natural sunlight and the levels of cannabinoids it will produce.

Strong, healthy plants and proper care yield strong seeds that germinate well. Strong seeds produce healthy plants and heavy harvests. Seeds stored too long will germinate slowly and have a high rate of failure. Vigorous seeds initiate growth within seven days or sooner. Seeds that take longer than a month to germinate could always be slow and produce less. however, some seeds take longer to germinate even under the best conditions.

The cask, r outer protective shell, n some seeds never properly seals, which allows moisture and air to penetrate. It also causes hormone concentrations to dissipate and make seeds less viable. Permeable seeds signal diseases and pests to move in. Such seeds are immature, white, fragile, and crush easily with slight pressure between finger and thumb. These are weak seeds and do not have enough strength t grow well.

Typically, a grower who acquires a bag of ten quality seeds from a reputable seed company germinates them all at once. Once germinated, the seeds are carefully planted and grown to adulthood. By and large, of the ten seeds, some will be male, some will be weak and grow poorly, and two or three seeds will grow int strong, super female. Of these “super” females, one will be more robust and potent than her siblings. This super female is selected to be the mother of countless super clones.


Cannabis seeds need only water, heat, and air to germinate. They do not need extra hormones to germinate. Seeds sprout without light in a wide range of temperatures. Properly nurtured seeds germinate in two to seven days, in temperatures from 70-90F. Temperatures above 90F impair germination. At germination, the outside protective shell of the seed splits, and a tiny, white sprout (radicle) pops out. This sprout is the root or taproot. Cotyledon, or seed leaves, emerge from within the shell as they push upward in search of light.


Soaking seeds in water allows moisture to penetrate the protective seed shell within minutes. Once inside, moisture continues to wick in to activate the dormant hormones. In a few days, hormones activate and send enough hormone signals to produce a radicle. The radicle emerges upward to bring a new plant into the world. Once the seed is moist, it must receive a constant flow f moisture to carry nutrients, hormones, and water so that it can carry on life processes. if germinated seeds are allowed to suffer moisture stress now seedling growth will be stunted.


Cannabis seeds grow best at 78F (25C). Low temperatures delay germination. High temperatures upset seed chemistry causing poor germination. Seeds germinate best under the native conditions where they were grown. Once germinated, move seedlings to a slightly cooler growing area, and increase light levels. Avoid high temperatures and low light levels, which cause lanky growth.

Air (oxygen)

Seeds need air to germinate. Moist, soggy growing mediums will cut off oxygen supplies and the seed will literally drown. Seeds germinate poorly when planted too deeply. Tender seedlings do not have sufficient stored energy to drive through layers of soil when sprouting. Sew seeds twice as deep as the width of the seed. A 0.125-inch (3mm) seed should be planted 0.25-inch (6mm) deep.

Household water contains enough dissolved solids (food) to nourish seeds through their first few weeks of life. Although seeds need only 30-50 ppm of nitrates before they germinate, any more will disrupt internal chemistry. Some growers chose to use distilled water that contains practically no dissolved solids to germinate seeds. In fact, a high concentration of dissolved solids (salts) in the water will actually pull moisture out of the seed!

Start feeding two to four weeks after seedlings have sprouted. Some growers wait until leaves yellow to begin feeding. Use a mild quarter strength solution. If yellowing persists, give seedlings a little more fertilizer.

Some seeds have a very hard outer shell, testa, and must be scarified to allow water to penetrate. To scarify, line a matchbox with a piece of fine-grain sandpaper or emery bard. Put the seeds in the matchbox and shake fr abut 30 seconds. Remove the seeds, and make sure they have been scuffed a bit. Just a little scuffing will allow water t enter and set germination in motion.

Pre-Soaking Seeds in Water

Soak seeds overnight in a glass of water. make sure seeds get good and wet so growth is activated. Do not let seeds soak more than 24 hours, or they might get too wet, suffer oxygen deprivation, and rot. Once soaked, seeds are ready to be placed between moist paper towels to sprout or be planted in a rt cube or fine, light soilless mix.

In a warm location, (70-90F), place seeds in a moist paper towel or cheesecloth, making sure they are in darkness. Set the mist cloth or paper towel in a vertical position (so tap root grows down) on a grate (for drainage) on a dinner plate.

Water the cloth daily, and keep it moist. Let excess water drain away freely. The cloth will retain enough moisture to germinate the seed in a few days. The seed contains an adequate food supply for germination. Prevent fungal attacks by watering with a mild two-percent bleach or fungicide solution. once seeds have sprouted and the white sprout is visible, carefully pick up the fragile sprouts (with tweezers) and plant them. Take care not to expose the tender rootlet to prolonged intense light or air. Cover the germinated seed with 0.25-0.5-inch of fine planting medium with the white root tip pointing down.

Direct Seed Germination

One of the problems with rockwool an be that the seeds heave out before germinating. this is why it is best to germinate seeds before putting them int rockwool substrate.

Once seeds have sprouted and the white sprout is visible, carefully pick up the fragile sprouts (wit tweezers) and plant them in a pre-drilled hole in the rockwool with the white tip pointing down. Take care not to expose the tender rootlet to prolonged intense air or light. Cover the germinated seed with one quarter or half inch of moist rockwool. Keep the rockwol evenly moist. Once the taproot sprouts, small fuzzy feeder rots will grow in 12-14 days.

Water penetrates the outer protective shell, continues to wick in, and activates dormant hormones that induce germination. Once a seed receives moisture, there must be a constant stream of moisture to transport nutrients, hormones, and water to carry on life processes. Letting germinated seed suffer moisture stress now will stunt or stop seedling growth. The black tip of the root tells me this is what has happened.

Soggy growing mediums cut oxygen supplies and cause seeds to drown. Planting seeds too deeply causes poor germination. Seedlings do not have enough stored energy to force through too much soil before sprouting. Plant seeds twice as deep as the width of the seed.

Seeds do not need any extra hormones to germinate. Average household water contains enough dissolved solids to feed seeds through their first few weeks of growth. Supplemental nutrients will disrupt internal chemistry. Some growers prefer to sue distilled water which contains virtually no dissolved solids to germinate seeds.

Sow (direct seed) or move the sprout into a shallow planter, small seed pot, peat pellet, or rooting cube. Keep the plating medium evenly moist. Use a spoon to contain the root ball when transplanting from a shallow planter. Peat pellets or root cubes may be transplanted in two to three weeks or when the rots show through the sides. Feed with t dilute, quarter-strength solution

Construct a moisture tent over the seedling container to help retain even grow-medium moisture. To build, place a baggie or piece of cellophane over the seeded soil. The cover will keep the humidity and temperature elevated. Seeds usually need only one initial watering when under a humidity tent. Remove the cover as soon as the first sprout appears above ground. Leaving the tent on after seeds sprout through soil will lead to damping-off and other problems.

Place planted seeds under an HID lamp to add dry heat while germinating. The heat dries soil, which requires more frequent watering. Place a heat pad or soil heating cables below growing medium to expedite germination. Marijuana seeds germinate and sprout quickest when the soil temperature is between 78-80F and the air temperature is 72-74F. but stems will stretch between internodes if temperatures exceed 85F for long.

Over-watering and under-watering are the biggest obstacles most growers face when germinating seeds and growing seedlings. Keep the soil uniformly moist, not waterlogged. Do not let the growing medium surface dry for long. Keep it evenly moist. Setting rot cubes or planting flats up on a grate allows god drainage. A shallow flat or planter with a heat pad underneath may require daily watering, while a deep, one gallon pot will need watering every three days or more. A properly watered flat of rockwool cubes needs water every three to five days when sprouting seeds. When the surface is dry (0.25 inch deep) it is time to water. Remember, there are few roots to absorb the water early in life, and they are very delicate.

Grow More Females from Seed

Environmental factors start influencing sex the moment the seedling has three pair of true leaves (not counting cotyledons). Environmental factors that influence sex determination of cannabis include but are not limited to:

Increasing the level of nitrogen makes more female plants. Lower the nitrogen level too create more male plants. Increase the level of potassium to increase male tendencies; lowering potassium eves encourages female plants. A higher nitrogen level and a lower potassium level for the first two weeks increases females.

Low temperatures increase the number of female plants. Warm temperatures make more male plants.

High humidity increases the number of female plants. Low humidity increases male plants.

Low grow medium moisture increases males.

More blue light increases the number of female plants. More red light increases male tendencies.

Fewer hours of daylight (e.g. 14 hours) increases the number of females. Longer days (e.g. 18 hours) make more male plants.

Stress: any environmental stress tends t yield more male plants when growing from seed.


When a seed sprouts, the white taproot emerges. Soon afterward, the cotyledon, also known as seed or seedling leaf, appears. The seed leaves spread out as the stem elongates. Within a few days, the first true eaves appear, and the little pant is now officially a seeding. This growth stage lasts for three to six weeks. During seedling growth, a rot system grows rapidly while green above ground growth is slow. Water and heat are critical at this point of development. The new, fragile root system is very small and requires a small but constant supply of water and warmth. Too much water will drown roots, often leading to rt rot and damping-off. Lack of water will cause the infant root system to dry up. As the seedlings mature, some will grow faster, stronger, and appear healthy in general. A little heat now will hep nurture small seedlings t a strong start. Other seeds will sprout slowly and be weak and leggy. Cull sickly, weak plants, and focus attention on the remaining strong survivors. Seedlings should be big enough to thin out by the third t fifth week of growth. Thinning out seedlings is very difficult for growers who pay $300 dollars for a few seeds!

Seedlings need at least 16 hours of light daily. They require less intense light now and grow well under fluorescent tubes for the first two to three weeks. Compact fluorescent and HID light can also be used. The compact fluorescent should be 12-18 inches and the HID 3-4 feet above seedlings for best growth.

The seedling stage is over when rapid foliage growth starts. Rapid growth above ground is the beginning of the vegetative growth stage. Plants need more room to grow; transplanting into larger container hastens development.

Storing Seeds

Store seeds in a cool, dark, dry place. Make sure to label containers! Some seeds will remain viable for five years or longer when stored properly. When 50 percent of the stored seeds do not germinate, the average storage life is over. But seeds a year old or older often take longer to sprout and have a lower rate of germination.

Dry seeds are temperature sensitive; they can be disinfected with a short application of heat. Low temperatures slow internal seed activity so are best for preserving seeds. You can use super-cold liquid nitrogen and cryogenics to store seeds for a long time.

Air, once it enters the outer seed shell, signals seeds to germinate. Viable seeds are preserved longer when vacuum-packed to remove all oxygen.

Seeds with a thin, outer protective shell never truly go dormant, because moisture and air cause hormone levels to slowly dissipate. Such seeds do not store well fr a long time.

Seed Pests

Seed pests become active when there is more than ten percent moisture content. When the growing mediums contains more than fifteen percent moisture, fungi become active. Excess fertilizer slows seedling growth and promotes fungus attacks.

Temperatures from 68-85F promote Pythium (damping-off) and rhixoctonia fungi. Cannabis seeds grow best at 78F. Most fungi reproduce fastest in a temperature range of 68-86F.

Keep a wary eye on problems. Nutrient overdose burns leaf tips and fringes, which can look like damping-off to the untrained eye. Do not fertilize. Applying a fungicide now will make the problem worse.

Marijuana Horticulture

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