Herb · Cannabaceae
Cannabis / Hemp
Cannabis sativa
Give it full sun, warm soil, and steady nitrogen, and Cannabis sativa races from seed to harvest in a single season.
Full sun
Every 2–7 days
59–86°F · 15–30°C
90–120 days
Overview
Cannabis sativa is a fast, hungry annual that goes from seed to a tall stand of stems in one season. It carries a long history as a fiber and grain crop, and the same species also grows for CBD and for its intoxicating flowers. Hemp and marijuana are not two plants but two ends of one species, sorted by how much THC the flowers hold.
How you grow it depends on what you want from it. Fiber and grain crops go in thick and stay unpruned, racing up to 4 m (157 inches) in good ground. Plants grown for CBD or flower get more room, a topping or two, and their lower branches cleared so light and air reach the buds.
Whatever the end use, the plant wants the same basics: full sun, warm well-drained soil, and plenty of nitrogen. It flowers when the days grow short in late summer, which sets the harvest clock. One thing to settle before you plant is the law, since growing Cannabis sativa is restricted in many places.
Care
The short version: full sun, deep well-drained soil that stays evenly moist without waterlogging, and a generous, nitrogen-forward feed through the vegetative stretch from spring planting to a late-summer harvest.
Light
Cannabis wants full sun, the more direct hours the better. It will get by in partial sun, but short light cuts both the fiber yield and the strength of the flowers, so give it an open, unshaded spot.
Water
Keep the soil evenly moist without ever letting it sit wet, since waterlogged ground breeds root disease. A field crop drinks roughly 25 to 30 inches of water over the season, with the heaviest demand during establishment and the vegetative push.
Soil
Plant in deep, well-drained loam rich in organic matter, with the aeration that lets the roots run. A pH between 6.0 and 7.5 suits it, and good drainage matters as much as fertility here.
Temperature
The plant runs best from 59°F to 86°F (15°C to 30°C). It needs warmth to get going and has no tolerance for frost, so wait for settled spring weather before it goes out.
Humidity
Around 40% to 70% is the comfortable range. The bigger risk is humidity that climbs and lingers inside a thick canopy, since damp, still air is what lets bud mold take hold.
Feeding
This is a heavy nitrogen feeder, often wanting 100 to 150 lb of nitrogen per acre depending on the end use. Feed through the vegetative season with a nitrogen-forward balanced fertilizer, matching the rate to whether you're after fiber, grain, or flower.
Pruning
Fiber and grain crops are left alone and never pruned. For CBD and flower production, top the plants and strip the lower branches so air moves freely and light reaches deeper into the canopy.
Repotting
As an annual field crop it isn't repotted. CBD starts get one transplant out of the plug tray after hardening off, and after that they stay in the ground for the season.
Size & spacing
Plants run from 1 to 4 m (39 to 157 inches) tall depending on the type and how thickly they're sown, with a spread of 30 to 90 cm (12 to 35 inches). Fiber crops go in dense, while flower plants want far more elbow room for airflow.
When to plant
Cannabis is a warm-season annual that will not tolerate frost. Sow CBD transplants indoors about a month before the last frost, set plants or seed out once the soil hits at least 50°F (10°C) in late spring, and harvest from late summer once shortening days have triggered flowering.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 4 to 6 weeks before last frost for CBD transplants
- Plant: After last frost when soil reaches at least 50°F, typically late spring
- Harvest: Flowering triggered by shortening daylength in mid to late summer; fiber harvested at early flower, grain at seed maturity, CBD at peak cannabinoid
Hardiness
USDA hardiness zones: 3–10
Temperature: down to -40°C
Troubleshooting
Most trouble with this crop shows up either in the lower leaves or deep inside the flowers. Catch the early signs and you can step in before a small problem spreads through a dense stand. Match what you see below, then act while it still helps.
Buds rotting gray-brown from the inside out
This is Botrytis, the gray mold that settles into thick flowers when the air sits humid and still. It works from inside the bud, so by the time the fuzzy gray sporulation shows on the surface the damage is already done. Cut out and destroy anything infected, open the canopy up for airflow, and harvest as soon as the crop is ready.
Fix:
- Remove and destroy infected material
- Increase airflow and reduce canopy density
- Harvest promptly when mature
Seedlings pinching off at the soil line and toppling over
This is damping-off, caused by soilborne fungi like Pythium, Fusarium, and Rhizoctonia that thrive in cold, wet ground. The stem goes water-soaked and dark right at the soil line, and the seedling simply falls over. Sow into warm, well-drained beds with clean, treated seed, and ease off the watering so the surface never stays soggy.
Fix:
- Improve drainage
- Avoid overwatering
- Plant into warm soil
Lower leaves fading to yellow while the plant is still growing
This is nitrogen deficiency, and it shows up often because hemp is such a hungry feeder. The oldest leaves pale first, then the yellowing climbs the plant as it pulls nitrogen up to the new growth. Confirm it with a tissue or soil test, then side-dress or fertigate to match the rate to your crop and growth stage.
Fix:
- Side-dress or fertigate with a nitrogen source
- Match N rate to end use and growth stage
Toxicity
This is one to keep away from animals. The plant's main active compound is THC, which is toxic to pets and causes clear neurological signs in cats, dogs, and horses. For people, the THC is psychoactive and stronger in marijuana types than in low-THC hemp, and growing the plant is legally restricted in many places, so check the law where you live before you plant.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Severe
Cats are hit hard by the THC. Watch for deep lethargy, a wobbly, uncoordinated walk, vomiting, dilated pupils, a dropping body temperature, and dribbling urine, and at higher doses the picture can slide into seizures or coma.
Dogs Severe
Dogs that get into any part of the plant or a dried product turn dull and unsteady on their feet, often vomiting, leaking urine, and reacting to sound and touch. A slow heart rate and a low body temperature are common, and severe cases bring on seizures or coma.
Horses Toxic
Horses are affected by the same THC. A horse that grazes the plant grows sluggish and unsteady, often off its feed, with a slowed heart rate and clear depression.
Rabbits Toxic
There's no safe nibble here. The THC acts on rabbits much as it does on other mammals, leaving them dull, off-balance, and sluggish, so keep every part of the plant out of reach.
Livestock Caution
Cattle, goats, and sheep generally leave the bitter plant alone, but an animal that does eat it can turn lethargic and unsteady from the THC. Fence stock away from any planting to be safe.
Birds Caution
Pet birds are small and sensitive, so even a little plant material or smoke can leave them dull and off balance. Treat it as off-limits.
People Caution
The plant's THC is psychoactive and intoxicating, and stronger in marijuana types than in low-THC hemp. Cultivation is legally restricted in many places, so check the laws where you live, and keep all plant material and any product well away from children and pets.
Keep all plant material, dried product, and edibles away from pets; THC is the primary toxic principle.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Cultivars are bred for very different jobs, from fiber and grain to high-CBD flower. These three show the range worth knowing.
Fedora 17
A monoecious French fiber and grain cultivar bred for low THC and stands that come up even.
Futura 75
A dioecious dual-purpose variety grown widely across Europe for both fiber and grain.
Cherry Wine
A photoperiod CBD type selected for high cannabidiol while holding THC within legal limits.
How to propagate
Cannabis grows readily from seed for field crops, or from cuttings when a grower needs exact copies of a chosen plant.
SeedEasy
Direct sow after last frost into warm soil for fiber and grain crops · 7 to 14 days to emergence
Seed is the standard route for fiber and grain crops. Direct sow after the last frost once the soil has warmed, and the seedlings emerge in 7 to 14 days. Starting from seed gives you genetic variability and the mixed male and female plants of a dioecious stand.
Stem cuttingsModerate
Take cuttings from vegetative mother plants before flowering · 2 to 3 weeks to root
Cuttings are how CBD and floral growers clone their best plants. Take them from vegetative mother plants before flowering begins, and they root in 2 to 3 weeks into uniform, high-cannabinoid females that match the parent.
Myths
Industrial hemp will get you high like marijuana.
Hemp is legally defined as Cannabis sativa with no more than 0.3 percent delta-9 THC. That's far too little to be intoxicating, which is exactly why the law draws the line where it does.
Hemp and marijuana are two different plant species.
They are the same species, Cannabis sativa. The split between them is a legal one set by THC concentration, not a botanical difference between two kinds of plant.