The cultivation of cannabis is the production of cannabis infructescences ("buds" or "leaves"). Cultivation techniques for other purposes (such as hemp production) differ.
In the United States, all cannabis products in a regulated market must be grown in the state where they are sold because federal law continues to ban interstate cannabis sales. Most regulated cannabis is grown indoors.Byrne, Genevieve (March 15, 2023). "Energy and Equity in Cannabis Cultivation" (PDF). Institute for Energy and the Environment, Vermont Law and Graduate School. Retrieved April 27, 2023.
Occupational diseases, including asthma, are an emerging concern in the rapidly expanding U.S. cannabis industry. Cannabis cultivation and processing technicians may be exposed to numerous respiratory hazards, e.g. organic particulate matter and dust from ground cannabis flower, mold, bacterial endotoxins, and pesticides. Employees exposed to ground cannabis without adequate controls are at risk of developing occupational asthma which can be fatal.
Botany
Cannabis belongs to the genus Cannabis in the family Cannabaceae. It may include three species, Cannabis indica, C. sativa, and C. ruderalis (APG II system), or one variable species. It is typically a dioecious (each individual is either male or female) annual plant.Cannabis sativa L. – Encyclopedia of Life . Eol.org. Retrieved on 7 August 2011.
C. sativa and C. indica generally grow tall, with some varieties reaching . Female plants produce tetrahydrocannabinol (THC) (up to 31% by weight) as the season changes from summer to autumn. C. ruderalis is very short, produces only trace amounts of THC, but is very rich in cannabidiol (CBD) an antagonist to THC, which may be 40% of the cannabinoids in a plant. C. ruderalis flowers independently of the photoperiod with the main factor for flowering being the age of the individual plants. However, commercial cross-bred hybrids containing both ruderalis, indica and/or sativa genes exist (usually called autoflowering).
Cultivation requirements Cannabis needs certain conditions to flourish.
Growth medium Soil is required, except for cannabis grown with hydroponics or aeroponics. Sufficient nutrients — commercial potting soils usually indicate this as "N-P-K = x%-y%-z%". This indicates the percentages of fundamental nutritional elements, i.e., nitrogen, phosphorus and potassium. Nutrients are often provided to the soil via fertilizers but such practice requires caution. A soil pH between 5.8 and 6.5. This value can be adjusted – see soil pH. Commercial fertilizers tend to make the soil more acidic, although manure has a less pronounced effect.
Warmth The optimal day temperature range for cannabis is . Temperatures above 31 °C (88 °F) and below 15.5 °C (60 °F) seem to decrease THC potency and slow growth. At 13 °C (55 °F) the plant undergoes a mild shock, though some strains withstand frost temporarily.The Marijuana Grower's Guide (1998) by Mel Frank and Ed Rosenthal, typed by Ben Dawson, revised 1992
Light Sun light or grow light can be used.
Under artificial light, the plant typically remains under a regime of 16–24 hours of light and 0–8 hours of darkness from the germination until flowering, with longer light periods being conducive to vegetative growth, and longer dark periods being conducive to flowering. However, generally cannabis only requires thirteen hours of continuous light to remain in the vegetative stage. The 'Gas Lantern Routine' is an alternate lighting schedule that has proven to be successful for growing cannabis, while saving a significant amount of energy. For optimal health, cannabis plants require a period of light and a period of dark. It has been suggested that, when subjected to a regimen of constant light without a dark period, cannabis begins to show signs of decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development. Typically, flowering is induced by providing at least 12 hours per day of complete darkness. Flowering in cannabis is triggered by a hormonal reaction within the plant that is initiated by an increase in length of its dark cycle, i.e. the plant needs sufficient prolonged darkness for bract/bracteole development (flowering) to begin. Some Indica varieties require as little as 8 hours of dark to begin flowering, whereas some Sativa varieties require up to 13 hours.
Water Watering frequency and amount is determined by many factors, including temperature and light, the age, size and stage of growth of the plant and the medium's ability to retain water. A conspicuous sign of water problems is the wilting of leaves."Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 153,154 Giving too much water can kill cannabis plants if the growing medium gets over-saturated. This is mainly due to oxygen not being able to enter the root system. Anaerobic bacteria start to accumulate due to waterlogged, stale conditions. They begin to consume plant roots, beneficial (aerobic) bacteria, as well as nutrients and fertilizer. When using soil as a growth medium, the soil should be allowed to dry down adequately before re-watering.
Humidity Humidity is an important part of plant growth. Dry conditions slow the rate of photosynthesis. Ideal levels of humidity for optimal growth are 40–60% RH.
Nutrients Nutrients are taken up from the soil by roots. Nutrient soil amendments (fertilizers) are added when the soil nutrients are depleted. Fertilizers can be chemical or organic, liquid or powder, and usually contain a mixture of ingredients. Commercial fertilizers indicate the levels of NPK (nitrogen, phosphorus, and potassium). In general, cannabis needs more N than P and K during all life phases. The presence of secondary nutrients (calcium, magnesium, sulfur) is recommended. Micronutrients (e.g. iron, boron, chlorine, manganese, copper, zinc, molybdenum) rarely manifest as deficiencies.
Because cannabis' nutrient needs vary widely depending on the variety, they are usually determined by trial and error and fertilizers are applied sparingly to avoid burning the plant."Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 164
Stages of development
Germination
Germination is the process by which a seed sprouts and a root emerges. Germination in cannabis can occur in as little as twelve hours or can take as long as eight days, depending on the cultivar and environmental conditions. Warmth, darkness, and moisture initiate metabolic processes such as the activation of hormones that trigger the expansion of the embryo within the seed. Then the seed coat cracks open and a small embryonic root emerges and begins growing downward (because of gravitropism), if placed in a proper growing medium. Soon (after 2–4 days) the root is anchored and two oval cotyledons (sometimes called "false leaves" or "seed leaves") emerge in search of light and the remains of the seed shell are pushed away. This marks the beginning of the seedling stage.
Peat pellets are often used as a germinating medium because the saturated pellets with their seedlings can be planted directly into the intended growing medium with a minimum of shock to the plant.
Scarification (artificial), example: Soaking the seeds in boiled water that is cooled down. Stratification (natural simulation), example: Soaking seeds either between wet paper towels, in a cup of water at room temperature, in wet peat pellets, or directly in potting soil.
Imbibition Imbibition of water through the membrane of the seed shell is the first step in the germination process for cannabis. Dry cannabis seeds are floating, a convenient way to verify a successful imbibition is to put them in water until they sink, which takes about six hours when submerged in an infuser, and about 12 hours when they are floating on water. Seeds that keep floating need scarification in order to absorb water.
Seedling
The seedling stage begins when the seed coat splits open and exposes the root and cotyledons. It lasts from 1 to 4 weeks, and is the period of greatest vulnerability in the life cycle of the plant, requiring moderate humidity levels, medium to high light intensity, and adequate but not excessive soil moisture.
Most indoor growers use compact fluorescent or T5 fluorescent lights during this stage as they produce little heat. High-pressure sodium and metal halide lights produce large amounts of radiant heat and increase the rate of transpiration in the plant which can quickly dry out seedlings with their small root systems.
Vegetative
Duration: 1–2 months indoors. In this stage the plant needs a significant amount of light and nutrients, depending on the genetics of the particular plant. It continues to grow vertically and produce new leaves. The sex is starting to reveal itself, which is a sign that the next stage begins. Concurrently the root system expands downwards in search of more water and food.
When the plant possesses seven sets of true leaves and the 8th is barely visible in the center of the growth tip, or shoot apical meristem (SAM), the plant has entered the vegetative phase of growth. During the vegetative phase, the plant directs its energy resources primarily to the growth of leaves, stems, and roots. A strong root system is required for strong floral development. A plant needs 1 or 2 months to mature before blooming. The plant is ready when it has revealed its sex. Plant size is a good indicator of sex. Females tend to be shorter and branchier due to their raceme type inflorescence than males, whose flowers grow in panicles. The males are then usually culled when they are identified, so that the females will not be pollinated, thus producing parthenocarpic fruits (popularly called "sinsemilla", meaning "without seed").
During the vegetative phase, cultivators generally employ an 18- to 24-hour photoperiod because the plants grow more quickly if they receive more light, although a warmer and cooler periods are required for optimal health. Although no dark period is required, there is debate among cultivators as to whether a dark period is beneficial, and many continue to employ a dark period. Energy savings often support using a dark period, as plants undergo late day decline and therefore lighting during the late night hours is less effective.
The amount of time to grow a cannabis plant indoors in the vegetative stage depends on the size of the flower, the light used, the size of the space, and how many plants are intended to flower at once, and how big the strain gets in "the stretch" (i.e., the first two weeks of flowering).
Cannabis cultivators employ fertilizers high in nitrogen and potassium during the vegetative stage, as well as a complete micronutrient fertilizer. The strength of the fertilizer is gradually increased as the plants grow and become more hardy.
Advanced cultivation methods include: training and trellising techniques such as Screen of Green (also known as SCROG), Sea of Green (also known as SOG) "Super cropping" and LST super cropping; and entire systems and methods such as the NIMBY no-dump method, Hempy Bucket, and the Krusty Freedom Bucket methods. Research into the production of cannabis for the drug Marinol and other more profitable and marketable forms of cannabis-based medicines has further pushed the envelope of cannabis cultivation in all forms of laboratory, both public and private. using a water or air-based growth medium (known as hydroponics and aeroponics respectively) the use of homemade, organic composted fertilizers