Herb · Cannabaceae
Cannabis / Hemp
Cannabis sativa
Give it full sun, warm soil, and steady nitrogen, and Cannabis sativa shoots from seed to a tall stand of stems 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 rises from a sown seed to a tall column of stems within one season. It has long served as a fiber and grain crop, and the very same species is also grown for CBD and for its intoxicating flowers. Hemp and marijuana are not two separate plants but two ends of one species, sorted by how much THC sits in the flowers.
How you grow it turns on what you want from it. Fiber and grain crops go in close and stay unpruned, the stems racing upward to as much as 4 m (157 inches) in good ground. Plants raised for CBD or flower get wider spacing, a topping or two, and their lower branches stripped away so light and air can reach the dense buds.
Whatever the end use, the plant asks for the same foundation: full sun, warm well-drained soil, and plenty of nitrogen. It comes into flower as the days shorten in late summer, and that sets the harvest clock. The one thing to settle before you sow is the law, since growing Cannabis sativa is restricted in many places.
Care
The short version: full sun, deep well-drained soil kept 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, and the more direct hours it gets the better it performs. It will scrape by in partial sun, but short light thins the fiber yield and weakens the flowers, so set it in an open, unshaded spot.
Water
Keep the soil evenly moist and never let it sit wet, since waterlogged ground breeds root disease. A field crop draws roughly 25 to 30 inches of water over the season, with the heaviest pull during establishment and the fast vegetative push.
Soil
Sink it into deep, well-drained loam rich in organic matter, with enough aeration that the roots can run freely. A pH between 6.0 and 7.5 suits it, and clean drainage counts for as much as fertility here.
Temperature
The plant runs best from 59°F to 86°F (15°C to 30°C). It needs real warmth to get moving and has no tolerance for frost, so hold off until settled spring weather before it goes outdoors.
Humidity
A range of 40% to 70% keeps it comfortable. The greater danger is humidity that climbs and lingers inside a thick canopy, because that damp, still air is exactly what lets bud mold take hold among the dense flowers.
Feeding
This is a heavy nitrogen feeder, often calling for 100 to 150 lb of nitrogen per acre depending on the end use. Feed it monthly through the vegetative season with a nitrogen-forward balanced fertilizer, matching the rate to whether you are after fiber, grain, or flower.
Pruning
Fiber and grain crops are left whole and never pruned. For CBD and flower production, top the plants and clear away the lower branches so air moves freely and light pushes deeper into the leafy canopy.
Repotting
As an annual field crop it is not repotted. CBD starts get a single transplant out of the plug tray after hardening off, and from there they hold their place in the ground for the season.
Size & spacing
Stems stretch from 1 to 4 m (39 to 157 inches) tall depending on the type and how thickly they are sown, with a spread of 30 to 90 cm (12 to 35 inches). Fiber crops go in dense and narrow, while flower plants want far more room for air to circulate.
When to plant
Cannabis is a warm-season annual with no tolerance for frost. Start CBD transplants indoors about a month before the last frost, set plants or seed out once the soil reaches at least 50°F (10°C) in late spring, and harvest from late summer once the shortening days have tripped the plant into flower.
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 turns up in one of two places: the lower leaves or deep inside the flowers. Catch the early signs and you can step in before a small problem runs through a dense stand. Match what you see below, then act while there is still time to help.
Thick buds going gray-brown and mushy at the core
This is Botrytis, the gray mold that buries itself in dense flowers wherever the air hangs humid and dead still. It eats outward from inside the bud, so by the time the fuzzy gray fur shows on the outer surface the soft brown rot at the center is already advanced. Cut out and destroy every infected piece, open the leafy canopy so air can move, and bring the crop in the moment it is ready.
Fix:
- Remove and destroy infected material
- Increase airflow and reduce canopy density
- Harvest promptly when mature
Tender seedling stems darkening at the soil line and folding over
This is damping-off, the work of soilborne fungi such as Pythium, Fusarium, and Rhizoctonia that move in wherever the ground stays cold and wet. The slim stem turns water-soaked and dark right at the soil line, pinches there, and the seedling simply keels over. Sow into warm, free-draining beds with clean, treated seed, and ease back on the water so the surface never sits soggy.
Fix:
- Improve drainage
- Avoid overwatering
- Plant into warm soil
The oldest leaves down low draining to pale yellow as the plant climbs
What you are seeing is nitrogen deficiency, and it turns up often because this is such a hungry plant. The lowest, oldest fan leaves wash out first, then the yellow creeps up the stem as the plant strips nitrogen from the bottom to feed the fresh growth at the top. Pin it down 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 chief active compound is THC, which is toxic to pets and brings on clear neurological signs in cats, dogs, and horses. For people the THC is psychoactive, 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 sow.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Severe
Cats take the THC badly. Look for deep lethargy, a wobbly, uncoordinated walk, vomiting, dilated pupils, a body temperature that drops, and dribbling urine. At higher doses the signs can worsen into seizures or coma.
Dogs Severe
A dog that gets into any part of the plant or a dried product goes dull and unsteady on its feet, often vomiting, leaking urine, and reacting to sound and touch. A slow heart rate and a low body temperature show up commonly, and the worst cases bring seizures or coma.
Horses Toxic
Horses react to the same THC. One that grazes the plant grows sluggish and unsteady, often turning off its feed, with a slowed heart rate and plain depression.
Rabbits Toxic
There is no safe nibble of this plant. The THC works on rabbits much as it does on other mammals, leaving them dull, off-balance, and sluggish, so keep every part of it well out of reach.
Livestock Caution
Cattle, goats, and sheep usually steer clear of the bitter plant, but any animal that does eat it can go lethargic and unsteady from the THC. Fence stock away from a planting to be safe.
Birds Caution
Pet birds are small and sensitive, so even a scrap of plant material or a whiff of smoke can leave them dull and off balance. Keep it off-limits.
People Caution
The plant's THC is psychoactive and intoxicating, and it runs stronger in marijuana types than in low-THC hemp. Growing it 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 jobs that pull in very different directions, from fiber and grain to high-CBD flower. These three mark out the range worth knowing.
Fedora 17
A monoecious French fiber and grain cultivar bred for low THC, throwing up stands that come in remarkably even.
Futura 75
A dioecious dual-purpose variety planted widely across Europe and worked for both fiber and grain.
Cherry Wine
A photoperiod CBD type selected for heavy cannabidiol while keeping THC inside legal limits.
How to propagate
Cannabis comes up readily from seed for field crops, or from cuttings when a grower needs exact copies of one 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 usual route for fiber and grain crops. Direct sow it after the last frost once the soil has warmed through, and the seedlings break the surface in 7 to 14 days. Going from seed brings 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 let CBD and floral growers clone the best plants exactly. Take them from vegetative mother plants before flowering sets in, and they strike roots in 2 to 3 weeks into uniform, high-cannabinoid females that mirror the parent.
Myths
Industrial hemp will get you high like marijuana.
Hemp is legally defined as Cannabis sativa carrying no more than 0.3 percent delta-9 THC. That is far too little to be intoxicating, which is exactly where the law has chosen to draw its line.
Hemp and marijuana are two different plant species.
They are the same species, Cannabis sativa. What separates them is a legal threshold set by THC concentration, not any botanical difference between two distinct kinds of plant.