This article presents common techniques and facts regarding the cultivation of the flowering plant cannabis, primarily for the production and consumption of marijuana buds. Cultivation techniques for other purposes (such as hemp production) differ. A basic description of hemp cultivation can be found in the US film Hemp for Victory.
- 1 Botany
- 2 Cultivation requirements
- 3 Stages of development
- 4 Outdoor cannabis cultivation
- 5 Indoor cannabis cultivation
- 6 Harvesting, drying and curing
- 7 Pests
- 8 Advanced cultivation methods
- 9 Genetics
- 10 Vegetative propagation (cloning)
- 11 Waste products
- 12 See also
- 13 References
- 14 Further reading
- 15 External links
Cannabis belongs to the genus Cannabis in the family Cannabaceae and includes four species, C. sativa, C. indica, and C. ruderalis "C. Afganica", (APG II system). It is typically a dioecious (each individual is either male or female) annual plant (life period: April–September).
C. sativa and C. indica generally grow tall (some varieties reach 4 m) and their females start the production of flowers rich in tetrahydrocannabinol (THC) (1% to 29%) 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), which may be 40% of the cannabinoids in a plant and is an antagonist to THC, and it flowers independently of the photoperiod and according to age. However, commercial cross-bred hybrids containing both ruderalis, indica and/or sativa genes exist (usually called autoflowering).
Cannabis needs certain conditions to flourish.
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%" the percentages of the fundamental nutritional elements, i.e., nitrogen, phosphorus and potassium. Nutrients are often provided to the soil via fertilizers but such practice requires caution.
- pH between 5.9 and 6.5. This value can be adjusted – see soil pH. Commercial fertilizers (even organic) tend to make the soil more acidic (decrease its pH).
The optimal day temperature range for cannabis is 24 to 30 °C (75 to 86 °F). Temperatures above 31 °C (88F) and below 15.5 °C (60F) seem to decrease THC potency and slow growth. At 13 °C the plant undergoes a mild shock, though some strains withstand frost temporarily.
Light can be natural (outdoor growing) or artificial (indoor growing).
Under artificial light, the plant typically remains under a regime of 16–20 hours of light and 4–8 hours of darkness from the germination until flowering, although the plant can use a full 24 hours of light without harm. There is an ongoing debate over the importance of the "dark period". It has been shown that, when subjected to a regimen of constant light without a dark period, most types of flora, including cannabis, will begin to show signs of decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development. There is no defined flowering "stage", unless you are discussing an auto-flowering variety (Cannabis Ruderalis). Typically, flowering is induced by changing the light schedule to 12 hours of light and 12 hours of 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  (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.
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. Too much water can kill young cannabis plants.
The additives in tap water can reduce plant growth and can be removed with reverse osmosis filtration but is expensive and produces poorer results than well or spring water.
Nutrients are taken up from the soil by plants. 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). During the vegetative stage, cannabis needs more N than P and K, while during the flowering stage, P is more essential than N and K. The presence of secondary nutrients (calcium, magnesium, sulfur) is recommended. Micro nutrients (e.g. iron, boron, chlorine, manganese, copper, zinc, molybdenum) rarely manifest as deficiencies.
Stages of development
Germination is the process in which the seeds sprout and the root emerges. In Cannabis it takes from 12 hours to 8 days. 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 circular embryonic leaves (cotyledons) emerge in search of light and the remains of the seed shell are pushed away. This marks the beginning of the seedling stage.
Germination is initiated by soaking seeds either between wet paper towels, in a cup of water at room temperature, in wet peat pellets, or directly in potting soil. 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.
The seedling stage begins when the seed coat splits open and exposes the root and round “seed leaves” or 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. HPS and MH 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.
The plant will naturally begin to develop identifiable sex characteristics in this stage after 4 to 6 weeks, but some growers will hasten this by switching to a 12/12 hour light period to induce flowering and, once sex is determined and the male plants are removed, returning the plants to the vegetation stage with 6 hour light period. However, forcing a plant to flower and then return to the vegetative stage adds significant extra growing time and has been shown to produce lower yields and reduce potencies by a factor of 2 to 3, so growers who wish to sex the plants as early as possible without these drawbacks take a clone of each seedling, root it, and force flowering in a separate growing area.
Duration: 1–2 months indoors. In this stage the plant needs all the light (at least 18 hours) and nutrients (food) that it can use, 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. Some newly developed strains (auto flowering hybrids) omit the vegetative stage and pass directly from seedling to pre-flowering.
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 tend to have fewer leaves near the top and females have more leaves surrounding the flowers. The males are then usually culled when they are identified, so that the females will not be pollinated, thus producing "sin semilla" ("without seed") buds.
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 period 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 N (nitrogen) and K (potassium) during the vegetative stage, as well as a complete micro nutrient fertilizer. The strength of the fertilizer is gradually increased as the plants grow and become more hardy.
The modification of a plant's growth habit is called training. Indoor cultivators employ many training techniques to encourage shorter plants and denser canopy growth. For example, unless the crop is too large to be extensively pruned, cultivators remove adventitious growth shoots, often called suckers, that are near the bottom of the plant and/or receive little light and will produce poor quality buds.
Many cultivators also employ other techniques:
Topping is the removal of the top of the apical meristem (dominant central stem), called the apex or terminal bud, to transfer apical dominance (the tendency for the apex to grow more rapidly than the rest of the plant) to the shoots emanating from the two nodes immediately beneath the pruning cut. This process can be repeated on one or both of the two new meristems, when they become apically dominant, with the same results. This process can actually be repeated nigh infinitely, but over-diffusion of apical dominance produces smaller, lower quality buds, so it is usually done no more than a few times. Topping also causes more rapid growth of all of the branches below the cut while the plant heals.
Pinching (also called super cropping) is similar to topping in that it causes lower branches to grow more rapidly, but the apical meristem maintain apical dominance, which is especially useful if the plant has already been topped. Pinching is performed by firmly pinching the apical meristem(s) so as to substantially damage vascular and structural cells but without totally breaking the stem. This causes lower limbs to grow more rapidly while the pinched tissue heals, after which time the stem resumes apical dominance.
LST stands for Low Stress Training and is another form of supercropping, many times referred to as LST super-cropping. This technique involves bending and tying the plants branches to manipulate the plant into a more preferred growth shape. This method of training works very well for indoor growers who need to illuminate their plants using overhead lights. Since light intensity greatly diminishes with increased distance (Inverse-square law), LST'ing can be used to keep all growth tips (meristems) at the same distance from the light and can achieve optimal light exposure. LST can be used in conjunction with topping, since topping increases axial growth (side shoots). Topping is often done a few weeks before beginning LST'ing. The training works by changing the distribution of hormones—more specifically Auxins—in the plant. LST'ing resembles the training of grape vines into their support lattices. Outdoor gardeners also employ training techniques to keep their plants from becoming too vertical.
Also called the stretch, this takes one day to two weeks. Most plants spend 10–14 days in this period after switching the light cycle to 12 hours of darkness. Plant development increases dramatically, with the plant doubling or more in size. (See reproductive development below.) Production of more branches and nodes occurs during this stage, as the structure for flowering grows. The plant starts to develop bracts/bracteoles where the branches meet the stem (nodes). Pre-flowering indicates the plant is ready to flower.
The flowering phase varies from about 6 to 22 weeks for pure indicas with their shorter flowering time than pure sativas. Mixed indica/sativa strains have an intermediate flowering time. The sex is clearly revealed in the first the flowering phase. Males produce little ball-like flowers clustered together like grapes called panicles. Most plants (except auto flowering strains that flower independently of photoperiod) begin to flower under diminishing light. In nature, cannabis plants sense the forthcoming winter as the Earth revolves about the Sun and daylight reduces in duration (see also season). If females are not pollinated (fertilized by male pollen) they start to produce buds that contain sticky white resin glands or trichomes in a final attempt for pollination by windborne male pollen. The trichomes produce resins that contain the largest amounts of THC and CBD, the two main psychoactive substances. Fertilized females continue to produce resinous trichomes but more plant energy is consumed by the production of seeds, which can be half the mass of a fertilized bract; thus, to maximize resin per gram, infertile cultivation is preferred.
Inflorescence that produce no seeds are called sin semilla (which translates to "without seeds" in Spanish, and is often misspelled as one word). Potent sin semilla is especially important to medical users, to minimize the amount of cannabis they must consume to be afforded relief. Cannabis with seeds is generally considered to be of inferior quality and/or grown with inferior technique.
Cannabis grown is induced into flowering by decreasing its photoperiod to at least 10 hours of darkness per day. In order to initiate a flowering response, the number of hours of darkness must exceed a critical point. Generally the more hours of darkness each day, the shorter the overall flowering period but the lower the yield. Conversely, the fewer hours of darkness each day, the longer the overall flowering period and the higher the yield. Traditionally, most growers change their plants lighting cycle to 12 hours on and 12 hours off since this works as a happy medium to which most strains respond well. This change in photoperiod mimics the plant's natural outdoor cycle, with up to 18 hours of light per day in the summer and down to less than 12 hours of light in fall and winter. Some 'semi-autoflowering' strains that have been bred exclusively for outdoor use, particularly in outdoor climates such as that of the UK, will start flowering with as much as 16–17 hours of light per day. Usually they can start flowering in July and finish far earlier than other strains, particularly those that haven't been bred as outdoor strains. Semi-autoflowering strains can be harvested before the weather in northern latitudes becomes very wet and cold (generally October), whereas other strains are just finishing flowering, and may suffer from botrytis (grey mold) caused by wet weather. Alternatively growers may artificially induce the flowering period during the warmer months by blacking out the plants for 12 hours a day i.e. by covering the plants with black plastic for example, which excludes all light during this period so the plant can flower even during long days.
Although the flowering hormone in most plants (including cannabis) is present during all phases of growth, it is inhibited by exposure to light. To induce flowering, the plant must be subject to at least 8 hours of darkness per day; this number is very strain-specific and most growers use 12 hours of darkness.
Flowers from certain plants (e.g. cannabis) are called bract/bracteole, and are (with cannabis) the most prized part of the plant. During the late period, the bract/bracteole are easily visible to the naked eye. Bract/bracteole development begins approximately 1–2 weeks after the photoperiod is reduced. In the first weeks of flowering a plant usually doubles in size and can triple. Bract/bracteole development ends around 5 weeks into flowering and is followed by a period of bract/bracteole “swelling”. During this time the buds greatly increase in weight and size.
Outdoor cannabis cultivation
Cannabis can be grown outdoors, either on natural soil or in pots of pre-made or commercial soil. Some strains perform better than others in outdoor settings, an attribute that depends on different conditions, variables and aspects. Outdoor marijuana strains, like most other strains, can be bought in numerous locations and over a hundred different cannabis strains that are bred for outdoor growing exist—many of these outdoor cannabis seeds are simply copies of other pre-existent strains or seeds with different names and descriptions.
To generate optimum quantities of THC-containing resin, the plant needs a fertile soil and long hours of daylight. This means THC production for outdoor growth occurs optimally anywhere within 35° of the equator. Typical growing regions include Mexico, Nepal, Northern India, many parts of Africa, Afghanistan, The United States and Australia.
In most places of the subtropics, cannabis is germinated from late spring to early summer and harvested from late summer to early autumn.
Outdoor cultivation is common in both rural and urban areas. Outdoor cultivators tend to grow indica-based strains because of its heavy yields, quick maturing time, and short stature. Some growers prefer sativa because of its clear-headed (cerebral) high, better response to sunlight, and lower odor emissions.
Growers cultivate on their own property or practice guerrilla farming i.e. to plant cannabis in remote areas such as forest clearings or mountain cliffs which they rarely visit. However, such a method is prone to theft – so much so that some ingenious growers even attach pots to trees to decrease this possibility. Guerrilla growing has given birth to the activist movement Operation Overgrow, where the plant is grown with the explicit purpose of introducing the cannabis plant into the natural ecosystem.
For outdoor cultivation, growers choose areas that receive twelve hours or more of sunlight a day. In the Northern Hemisphere, growers typically plant seeds in late May or early June to provide plants a full four months of growth. Harvest is usually between mid-September and early October. In North America, northern locations are preferred (North Coast of California and British Columbia being particularly notable), but southern locations (such as Maui, Hawaii) are also known to be good producers.
Where local laws do not permit growing cannabis, cultivators sometimes grow in forests or rugged and rural areas where the local population is unlikely to find the crop. Cannabis is also grown hidden by a crop that is taller, such as maize. This is reported by the United States government to be common in the midwestern states. Bamboo and elderberry are also used as camouflage companion plants.
Some government agencies, including the Drug Enforcement Administration (DEA), have claimed that in State and National Parks people have been injured by cannabis farmers protecting their crops using booby traps; no arrests or convictions for this had been made as of 2007[update].
|This section does not cite any references or sources. (September 2013)|
Often, simple camouflage techniques can avert detection, such as mixing cannabis plants with other bushy, leafy species. Plants started outdoors late in the season do not grow as tall, attracting less attention when placed next to plants of similar or taller stature.
A common technique used by many outdoor growers is to place a potted plant in a hole in the ground—this can reduce a plant's height, reducing its visibility. Also, some growers top the plant when it is only 12 inches (30 cm) high, and grow the two tops horizontally along a trellis.
Law enforcement agencies often monitor certain geographical areas, particularly areas of countryside with a significant history of outdoor cannabis cultivation. From helicopters, they use infrared cameras and other equipment in an attempt to "see" reflective signatures of the vegetation below. Cannabis has a slightly different reflectivity at certain wavelengths than other rural crops, such as corn. Law enforcement agencies have attempted to use technology to aid in the detection of outdoor crops because many growers hide cannabis among other plants, making detection with the "naked eye" difficult, even from the air.
Most cultivation is therefore conducted indoors, either in greenhouses (in which other plants are often used to camouflage the plants), or in specific grow rooms or shelters.
Indoor cannabis cultivation
Cannabis can be grown indoors in a soil-like medium under artificial light, adding fertilizer when the plants are given water. Cultivating cannabis indoors is more complicated and expensive than growing outdoors, but it allows the cultivator complete control over the growing environment. Plants of any type can be grown faster indoors than out due to 24-hour light, additional atmospheric CO2, and controlled humidity which allows freer CO2 respiration.
Plants can also be grown indoors through the use of hydroponics.
To grow plants indoors, a growing medium (e.g. soil or growing substrate), water, nutrients, light and air need to be supplied to the plant (with the exception of aeroponic cultivation, in which case a growing medium is not required).
Supply of light
To determine the appropriate lighting (and the best lamp to use), the specific needs of the plant must be considered, as well as the room size and ventilation. To arrange optimal lighting, the lighting present in the plant's natural environment must be imitated. Cannabis plants also require both dark and light photoperiods, so the lights need a timer to switch them on and off at set intervals. The optimum photoperiod depends on each plant (some prefer long days and short nights and others preferring the opposite, or something in between).
Most plants grow under most light spectra, but always prefer a full spectrum light. A test performed by Ed Rosenthal found that when a room was set up using both high pressure sodium (HPS) and metal halide (MH) lamps, the plants in between the two lights did better than those under MH alone but not as well as those under HPS. However, certain plants (as cannabis) can be grown successfully under both types of light. MH is used for the vegetative phase of growth, as it encourages short inter nodes (distance between sets of leaves), and inhibits cell elongation, creating a shorter, stockier plant. Metal halide lamps produce more ultraviolet radiation than high pressure sodium lamps, which may play a role in increasing the flowering (and for certain plants such as cannabis, the amount of psychoactive substances as THC) of the plant. High pressure sodium lamps trigger a greater flowering response in the plant and are thus used for the second (reproductive) phase of the growth, or they are used by those people who only wish to purchase a type of single lamp. If high pressure sodium lamps are used for the vegetative phase, plants usually grow slightly more quickly, but also have longer inter nodes, and may be taller.
Recent advancements in LED technology have allowed for diodes that emit enough energy for cannabis cultivation. These diodes can emit light in a specific nanometer range, allowing for total control over the spectrum of the light. LEDs are able to produce all of their light in the photosynthetically active range (PAR) of the spectrum. One major shortcoming of LED’s remains their lack of intensity. Due to this lack of intensity LED is only able to excel at growing plants in the vegetative stage of growth, or when flowering with extremely small canopies (micro grows).
LED grow lights are still considered an experimental technology in cannabis cultivation. Due to their high cost and low light output they remain unused by the commercial grower. The market remains flooded with cheap quality LED lights that do not produce yields comparable to what growers are accustomed. Many companies are using single watt LED chips, which have notoriously produced low yields and wispy results. When considering purchasing any grow light, one should carefully examine both the spectrum and the intensity of the light.
Reflectors are often used in the lamps to maximize light efficiency. Plants or lights are moved as close together as possible so that they receive equal lighting and that all light coming from the lamps fall upon the plants. Maximum efficiency can be obtained by creating a slightly concave canopy such that the periphery and center of the canopy are both at the optimum distance from the light source. Often, the distance between lamp and plant is in the range of 0.6 m (2 ft) with high pressure sodium lamps, to 10 cm (4 in) with other lamps, such as compact, large and high-output fluorescent lamps. With proper cooling any light type can be moved extremely close to plants to combat the inverse square law, but there are reasons to keep some distance from the canopy regardless of heat concerns; excessive light can cause bleaching of the plant material and the total canopy area contacted by light is decreased as the source is moved closer. Maximum efficiency should be obtained by maximizing the average light intensity (measured in PAR watts) per square foot times the number of square feet of plant matter contacted. Some cannabis cultivators cover the walls of their grow-room with some type of reflective material (often Mylar or Visqueen), or alternatively, white paint to maximize efficiency.
One commonly used covering is 150 µm (6 mils) PVC plastic sheeting that is white on one side and black on the other. The plastic is installed with the white side facing into the room to reflect light, and the black facing the wall, to reduce fungus and mold growth. Another common covering is flat white paint, with a high titanium dioxide content to maximize reflectivity. Some growers consider Mylar sheeting to be very effective when it lines grow room walls, along with Astrofoil (which also reflects heat), and Foylon (a foil-laminated, reinforced fabric).
Control of the atmosphere
When growing indoors, the cultivator should maintain as close to an ideal atmosphere inside the grow-room as possible. The air temperature should be maintained within a specific range, typically with deviations no larger than 10 °C with a cooler night and warmer day. Adequate levels of CO2 must be maintained for the plants to grow efficiently. It is also important to promote vigorous air circulation within the grow room, which is usually accomplished by mounting an extraction fan and one or more oscillating fans.
Assuming adequate light and nutrients are available to plants, the limiting factor in plant growth is the level of carbon dioxide (CO2). Plants grown with supplemental carbon dioxide grow more quickly, have larger stomata (Pores), and can use more light. According to Ed Rosenthal, however, ambient heat in the grow room must be increased from 75 °F (24 °C) to between 80 and 85 °F (27 and 29 °C) in order to fully utilize the increased CO2 concentration (the increase in heat allows for a faster metabolic rate). Ways of increasing carbon dioxide levels in the grow-room include: bottled carbon dioxide, carbon dioxide generators, a milk jug and yeast solution (in which yeast grows in a container thereby emitting CO2), a baking soda and vinegar mixture in a container, or dry ice.
Certain plants (e.g. most strains of cannabis) emit a distinctive odor during their reproductive phase. This presents difficulties to those who are cultivating in places where it is illegal, or for growers who may prefer discretion for other reasons. The most common way of eliminating odor is by pulling odorous air through a carbon filter. Many cultivators simply attach a large carbon filter to their air extraction system, thereby filtering any smell before the air is expelled from the grow-room. Another way of eliminating odor is by installing an ozone generator in the extraction ducting. The air is forced past the ozone generator by the extraction fan, and the odorous air is neutralized as it mixes with the ozone; however the cultivator must ensure that the air is thoroughly mixed before it is expelled outside, lest some odor escape. Care must be taken to prevent excessive ozone concentrations in the garden itself, or where it might be inhaled by the grower or his/her family. Ozone itself has a distinctive smell and is harmful to living things, although the molecule breaks down quickly (20 minutes to an hour) in atmospheric conditions.
Indoors there are numerous configurations that people utilize to grow quality cannabis. Some growers will convert an entire room or closet, making it devoted to growing cannabis. A relatively new configuration involves the use of grow tents. These are plastic or metal framed tents which are covered in a strong flexible reflective plastic and have light proof zipper doors. Tents come in all sizes and many already have holes for exhaust fans/ducting as well as mounts for HID lamps.
Some growers will construct grow cabinets made out of an old refrigerator, cabinet, dresser drawer or similar.
Indoor growing has become increasingly common over the past decade because of the increased availability of equipment, seeds and instructions on how to cultivate. So-called grow-ops (growing operations, often located in grow houses) are seen by many marijuana enthusiasts as a much cheaper way to gain a steady, higher-quality supply of cannabis. On a larger scale they have proven a viable commercial venture, with some law enforcement agencies finding grow-ops large enough to yield several kilograms of cannabis. More expansive grow-ops are generally more susceptible to detection than smaller operations.
Because individual grow light power generally ranges from 250 watts to 1000 watts or more and because the lights remain lit for a long time each day, differences in utility bill costs are a significant security issue. It is not uncommon for power companies to work with law enforcement if they see a significant increase in power usage relative to a household's previous electricity costs or if power is being stolen by bypassing the meter. Employing energy saving methods is a common way to alleviate this, for instance; switching off light bulbs when leaving rooms, purchasing energy efficient appliances, using TVs or computers less, buying lower power light bulbs and so forth.
Some plants (e.g. cultivars of Cannabis sativa subsp. indica), can give off strong odors as they grow, resulting in detection of illegal growing operations. Growers frequently use carbon scrubbers and ventilation to control odors. This typically involves forcing air from the grow room through a device containing activated carbon, then venting it outdoors. Others use an ozone generator. Ozone reacts with odor molecules in the air, permanently eliminating them. However, ozone can build up to levels that may be hazardous both for grower and plant. As a last resort, keeping windows firmly shut and using strong air fresheners can control smells. Checking outside to see if any smells are emanating from indoors is often a necessary precaution, as many growers become acclimated to the smell, and fail to realize just how pervasive the odor may be. Many store plants in more isolated areas such as a basement or attic to prevent smell detection. Another less common solution is to simply grow a strain with a weaker odor.
Storing plants and lights away from windows and areas that visitor may see is also common, as is keeping the plants in an attic or basement. Some growers, finding this impractical, may cover windows with light-resistant materials. This can solve the problem of escaping bright light but may arouse suspicion amongst neighbors and local residents.
Many cultivators face the risk of fire. Fires normally originate from faulty electrical equipment or wiring. Shoddy fixtures and sockets, improperly grounded equipment, and overloaded circuit breakers are some of the most prevalent causes. Because of the large amount of electricity needed for large-scale cultivation, old or damaged wiring is prone to melt and short. Some commercial growers steal power to hide electricity use, and many do not ensure that their wiring is safe. Many growers adapt light cycles so that the lights are on when they are home and off when they are away.
Another fire hazard is plants making contact with hot HID bulbs. Growers using fluorescent bulbs with reasonable air circulation do not have this problem. Word of mouth can be as much a threat to growers as any of the above issues. Often, a few sentences of conversation overheard can result in a tip-off and thus speedy detection. It is for this reason that many growers are reluctant to talk about their cultivation.
For houses used as grow-ops, the interiors may have received significant structural, electrical and heating system modifications not in accordance with applicable building, natural gas and electrical codes, such as overloaded existing electrical system or a bypass circuit to avoid paying for the electricity required to power the high intensity light bulbs and fans, disconnected furnace venting, or holes in floors and walls for increased airflow. These changes replicate warm, humid climates where hybrid plants flourish and produce high potency cannabis. Such modifications may result in considerable structural damage. Cultivation over a period of time may lead to moisture and toxic mold.
Grow-op homes appear to be maintained in their normal fashion on the outside. Nonetheless, there are plenty of tell-tale signs, such as occupants often avoid their neighbors, a "beware of the dog" sign, and melted snow in the winter (because of the higher-than normal heating to cultivate these plants).
Contractor and television presenter Mike Holmes said that while houses formerly used for growing cannabis could be bought very cheaply from banks or other owners, repairs and remediation could cost around $100,000 CAD, which may exceed price savings. Holmes noted that in one of his past jobs on Holmes on Homes, he and his crew gutted the entire house after discovering it was a grow-op.
In some municipalities, after the police raid a grow-op house they are required to contact the municipality to ensure that it is put back in good condition before being offered for sale, while real estate agents and sellers may be required by law to disclose that the home had been a grow-op. Home inspectors routinely fail to detect tell-tale signs that a house had been used as a grow-op.
Harvesting, drying and curing
There may be different goals when harvesting a plant:
- Seeds are harvested when fully developed and often after the accompanying buds have begun to deteriorate.
- Hemp grown for fiber is harvested before flowering,
- Cannabis grown for cloning is not allowed to flower at all.
When the goal is to ingest the harvest, the production of unfertilized inflorescence or bud (called sin semilla) is the goal. A typical indicator that a plant is ready to be harvested for smoking, is when 2/3 of the pistils have turned from clear or white to reddish brown. In general, harvesting consists of drying and curing. Curing is essential for the even distribution of moisture in the product.
- Dry: Buds left in well ventilated dark place
- Cure: Buds stored in sealed bag and left in dark place
A popular method is the following, with alternate curing and drying, such as:
- Dry 24 hours
- Cure 6 hours
- Dry 12 hours
- Cure 6 hours
... and repeat until product is deemed ready.
Usually, In 3–4 days buds are ready for consumption.
Cannabis buds are typically harvested when fully ripe. Generally, ripeness is defined as when the white pistils start to turn dark yellow, orange, light to mid red, etc. and the trichomes, (vernacular: crystals), barely begin to turn milky from clear. These trichomes can range from completely clear (generally deemed underdeveloped), to amberish-red. Ideally, professionals use a decent power magnifying glass, a brix meter to measure "sugar" content, and a microscope. The potential seed pods swell with resins usually reserved for seed production, thus improving the quality of the buds (called colitas, Spanish for "little tails"), which swell to form full "colas" (Spanish for "tails"). Harvesting slightly early will maximize the THC content. Harvesting later reduces the THC content and maximizes the sleep inducing effect desired by some medical users.
The plants are dried at room temperature in a dark space. It is actually optimal to keep the temperature between 60 and 70 °F (16 and 21 °C) because many terpenoids (molecules that are partially responsible for the psychoactive effects but also largely responsible for the odor of the plant) evaporate at temperatures beyond 70 °F (21 °C). This process can take from a few days to two weeks, depending on the size and density of the buds and the relative humidity of the air. Humidity should be kept between 45% and 55% humidity. Higher humidity will create a mold and mildew risk, while lower humidity will cause the material to dry too quickly. If the plant material dries too quickly, some of the chlorophyll will fail to be converted to a different chemical form which will result in a sub-optimal taste and a harsher smoke when combusted and inhaled. Stable temperature preserves cannabinoids well. Some believe flowers should be hung by their stalks, allowing the internal fluids of the plant to remain in the flowers. Others believe the cut stem is simply a handy non-sticky place from which to hang the plant. Roots are removed, and when the stems in the middle of the largest buds can be snapped easily, the plant is considered dry enough to be cured. Drying is done in a dark place, as THC resins deteriorate if exposed to light and the degradation product CBN forms, significantly altering the cannabinoid profile of the dried flowers.
Drying the harvest is generally not considered risky by novice indoor growers of cannabis who would like to assume that they have gotten safely to the end of their "grow" by the time they are harvesting their plants. However, generally speaking most will underestimate the sheer scale of odour produced during the cropping, moving and hanging plants to dry. Indoor growers in areas where cultivation is illegal may consider this an obstacle in their overall efforts as the first three days of drying produces very large amounts of discernible odour (organic molecules) which the grower himself/herself may be de-sensitised to. These will be evaporating and likely discernible to others anywhere in the vicinity of the general area. In populated areas consideration of containment & concentration (i.e. filters) of odour molecules may be employed to reduce risk. In less populated areas with good air movement dissolution and dispersal techniques for odour management may be employed i.e. ventilation from high points such as a chimney or roof vents. Whatever method is to be employed, newbie growers in illegal areas would do well to not underestimate the sheer volume of organic molecules being dissipated into the air when harvesting.
The curing process continues breaking down sugars and helps develop taste and smoothness of smoke. Usually, the dried product is packed (not compressed) into airtight glass canning jars. Initially, the product is checked periodically (every few hours) to make sure it was properly dried and has not re-moistened itself. After several days, when the product is dried to satisfaction, the jars are sealed off and opened just once a week. Curing is highly varied—the minimum is usually two weeks. Some growers even cure as long as six months, while others do not cure at all. As with tobacco, curing can make the cannabis more pleasant to smoke. For the same reasons as when drying, curing jars are stored in a cool, dark place. Failure to vent the jars causes moisture that leads to quick mold build up.
A recent method of curing is called water curing. This method is quicker and can improve a lower quality product. Using this method, nutrients can be fed to the plants right up until they are harvested because the water flushes out harmful chemicals (such as the ones used to feed the plants) as well as proteins, sugars, pigments and some resins. This also increases the THC to weight ratio though many[who?] believe the finished product is not as attractive as using a standard dry and cure method.
Tincture. Ethanol is used to extract cannabinoids from the cannabis plant (THC is soluble in alcohol). The extraction process takes longer, but results in an edible product. Cannabis stems, leaves and buds can all be used. The resulting mixture can be eaten straight, mixed with food or even smoked. Many smokers prefer to dip cigarettes in the mixture, which allows them to smoke in public without detection. Contact with direct flame causes this liquid to lose its THC content, as THC vaporizes at 157 °C (315 °F). Smokers usually heat the liquid and inhale the vapors through a straw.
Hash is a THC concentrate containing the extracted heads of the marijuana plant's trichomes that contain primarily all of the plant's psychoactive THC. The "trim leaf" (small leaves surrounding the flowers) are usually coated in a large amount of trichomes which are collected by various means to make hash. One simple method of collection is to separate the trichomes from the trim leaf using a basic screen; plant matter containing trichomes is run over or beat against the screen to separate the trichomes. Another method involves freezing the trim and then agitating it with ice to separate the trichomes, the mixture then is filtered through screen bags of decreasing screen sizes ranging from 25-200 µm which capture the plant matter and allow the trichomes to pass to the bottom bag where they collect into a wet paste. The paste is pressed to extract most of the water and pressed into cakes and dried. In a dry-ice sifting process the trim leaf is placed in a filter bag with dry ice and shaken to allow a very pure concentration of trichomes to pass through which can be kept as powder or pressed into cakes.
Hash oil is an extract that is formed when a solvent, commonly including; butane, isopropyl alcohol, ethanol, hexane, or toluene, is used as to dissolve THC concentrations. The plant particulates are filtered out and then the solvent carrying the soluble resins is evaporated or purged under vacuum. The resultant oil may have a high THC content (depending on the parent material) and is used in various cannabis-based products or smoked or vaporized as a concentrate. Delta 9 THC (D9 THC) is strongly soluble in petroleum ether and less so in ethanol. Adding petroleum ether to the tincture will extract D9 THC, leaving water soluble chemicals in the ethanol (certain cannabinoids, proteins, chlorophyll, etc.). Butane is a more selective solvent which typically carries lower amounts of undesired soluables, resulting in a more pure THC. Alcohol is less selective than butane, carrying other types of plant matter such as chlorophylls and lipids, resulting in a less pure hash oil, freezing the plant matter prior to making hash from alcohol can prevent some chlorophyll from being carried. Carbon Dioxide (CO2) has also been used to extract hash, but special laboratory equipment is needed since CO2 only functions as a solvent under high pressure.
Brick weed is a curing and packaging method of cannabis cultivation that consists in drying the bud for a short period, if at all, and pressing it with a hydraulic press, compacting the whole plant (bud, stems and seeds) into a brick, hence the name brick weed. This method is mainly used in the top cannabis producing countries like Mexico and Paraguay where it is largely exported. Brick weed has a low THC level and less potent aroma and taste.
Outdoor growers are likely to confront issues regarding pests. In any case (indoor or outdoor), experienced growers recommend caution when using chemical pesticides, for they may have toxic effects on the environment, the plants themselves and in turn cannabis consumers. As a general rule, experts mandate the deployment of pesticides clearly marked as "safe to use on food crops". Substances proven to induce little or no harm include:
- Pyrethrins: Organic and very effective, although sometimes hard to find. Often expensive because of high production cost.
- Azadirachtin: Meets most criteria to be classified as natural insecticide. Biodegradable, non-toxic to mammals. Usually cheaper and easier to find than pyrethrins.
Indoor growers also have problems with pests, usually caused by the grower or a pet bringing them in from the outdoors. If caught too late, eradication of many destructive insect species indoors may be impossible until all infected plants are removed from the space and sterilization methods employed.
Advanced cultivation methods
These methods include:
- using a water or air-based growth medium (known as hydroponics and aeroponics respectively)
- the use of homemade, organic composted fertilizers
- 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.
The emphasis on advanced cultivation techniques, as well as the availability of hybrid strains (with names like Northern Lights, Master Kush, NYC Diesel), is believed to be a factor in the increase in the overall quality and variety of commercially-available cannabis over the past few decades. The internet in particular has brought together widely diverse genetics from around the world through trading and purchasing. However, well-grown heirloom strains (e.g. island sweet skunk, fruity Thai etc.) are used to produce 1 gram per watt hour (g/Whr) harvest.
In contrast to the "Screen of Green" method, Sea of Green (or SOG) growing depends on the high density of plants (as high as 60 per square meter) to create uniformity in the crop. In this technique, which is often grown in hydroponic media, only the colas of the plants are harvested. Containers are used to enforce the geometric distribution of flowers and plant material, as well as their exposure to lighting and atmosphere. Sea of green is popular with commercial cultivators, as it minimizes the amount of time a plant spends in vegetative stage, and allows very efficient light distribution, keeping the plants much closer to the lights than when grown to full size.
SCROG, short for SCReen Of Green, is an advanced training technique for cultivating Cannabis, mainly indoors. Closely resembles SOG (or Sea Of Green) with the difference being that SCROG uses extensive training to produce the same field of bud effect with only one plant. Medical growers may find this a helpful technique to maximize harvest if they are only allowed a certain number of plants. A screen such as chicken wire is hung over plants so that the tips of branches are kept at the same level. This allows even light distribution to all of the nodes/bud sites. Once the flowering stage begins, the flower tips reach through the wire and are at relatively equal distances from the light source.
Vegetative state: The plant should remain in the vegetative state until 70 to 80 percent of the net is full. As a branch reaches three to four inches above the wire it is pulled back under the wire and so trained to grow horizontally until flowering. Because of the amount of plant required to fill the net, the vegetative period may require longer than normal to be ready for flowering.
Timing: Timing is vital to the success of a SCROG grow. If the net is not full at harvest, valuable space has been wasted. If the net is too full then the buds will be too crowded to develop properly. Knowing how a plant grows can help to visualize when to flower for maximum effect.
Hydroponic cultivation generally occurs in greenhouses or indoors, although there is no practical obstacle to growing outdoors. In general, it consists of a non-soil medium exposed to a nutrient and water flow.
There are many types of hydroponic systems. If the nutrient solution floods the loose growing medium and recedes for aeration, this is an ebb and flow or flood and drain system. Systems that gradually drip solution onto the medium are drip systems. Systems that intermittently spray roots floating in air are called aeroponic systems. If aerated water runs down a channel lined with a film of rooting medium, this is a nutrient film technique system. A series of tubes intermittently running high flow nutrient solution into the tops of growing containers use a top feed system. Aquaponics, another growing method that is gaining popularity, employs the use of fish water and recirculates that water from the fish holding tank to the growing bed.
Hydroponic systems greatly increase aeration of plant roots, and increase control of nutrient uptake. Hydroponic systems are decidedly more difficult to operate for the amateur or hobby grower, as over-fertilization is common, because there is no soil to act as a nutrient buffer. For this reason, many growers now use coconut fiber as a soil-less medium because of its high drainage and buffering capabilities that make it almost impossible to over-fertilize. Additionally, if a hydroponic system fails, the crop has a high probability of dying as the roots rapidly dry out (this is especially true of aeroponic systems).
There is now a new breed of hydroponic configurations such as the Omega Garden, the B-Pod and the EcoSystem Vertical Growing System that use circular designs to maximize efficiency. This consists of plants being placed or, in the case of the Omega Garden, revolving around a central light that makes maximum use of the light output.
Selection of mother plants
An important factor while cultivating photoperiod independent (non-autoflowering) cannabis is selecting the best genetics for one's crop. This is frequently done by selecting one or more known strains, or strains with preferred genetics, and then growing a number plants to find which exhibit the characteristics most desirable. These genetics should typically yield at least 1 gram per watt per month of flower.
Plant characteristics generally selected for include:
- Overall yield
- Time to fruition
- Resistance to pests
- Geometric traits (uniformity, compactness, flower density, etc.)
- Flavor and/or aroma
- Appeal to end buyer (known as "bag appeal")
- Psychoactive qualities
- Trichome density and type (stalked or sessile)
Autoflowering cannabis strains, also known as day-neutral cannabis are a relatively new development for the home cultivator. These autoflower strains are usually crosses that contain high percentages of well known photoperiod strains and C. ruderalis with its autoflowering characteristics. The plant produced from an autoflowering seeds will transition from a very short vegetative period, usually 2 to 3 weeks from germination, into flowering regardless of photoperiod. The result is that no separate vegetative and flowering lighting environment are needed. Flowering is dependent on the plants age not the time of year or ratio of light to dark hours. Autoflowers will finish from seed in 12/12, 18/6, 20/4 or even 24/0 lighting.
The first 'autoflowering cannabis seed' which came on the market was the Lowryder #1. This was a hybrid between a cannabis ruderalis, called William’s Wonder and a Northern Lights #2. The genetics of the ruderalis was still highly present which made for a very low yield and little psychoactive effect.
After many years of autoflower inbreeding seed makers have now come up with autoflowering strains that can produce yields close to the regular strains and still are flowering independent from the light cycle. The first autoflowering strains came from breeder STICH but now almost all major seed companies have their strains of super autoflowers that can grow up to 2 meters and produce yields up to 900 g/m2 of growth.
Instability of gender is a desirable trait in the wild, where reproduction is the most urgent goal. In cultivation, gender predictability is more helpful, because female plants that have not been pollinated are the most productive of the psychotropic material. It is possible to use a combination of cloning and "shocking" of plants to get them to produce feminized seeds that reliably produce female offspring. A clone retains the same sex throughout its life, so the clone of a female plant is also female.
Environmental stresses sometimes create pollen bearing male flowers on female plants—known as hermaphroditism or 'hermying'.
A method used by organic growers and promulgated by the cannabis breeder Soma, is called 'Rodelization', or letting un-pollinated female plants live several weeks longer than the normal harvest time. In such plants a hermaphroditic trait self-expresses in an effort to continue the genetic line.
Some vendors of feminized seeds assert that hermaphroditic "parents" do not create reliable feminized seeds, since the offspring may retain the tendency of hermaphrodytism. Others believe that this method utilizing auto-hermaphroditic traits is offset by grower observations that the tendency to auto-switch sex is no greater in plants grown from seeds made this way, than occurs naturally.
Colloidal silver (commonly abbreviated CS) suppresses ethylene production in bud sites, stimulating male characteristics. Spraying selected leaves, branches and – in cases where a large amount of seed is desired – whole plants with colloidal silver solution has become a preferred method of obtaining feminized seeds. Most plants treated with CS will turn intersex within 2 weeks of triweekly treatment, producing viable pollen within 4. Gibberellic acid has also been used for the same purpose, but it is harder to acquire than colloidal silver and can be difficult to dissolve into solution. One method of obtaining colloidal silver utilizes a small direct current power supply and two pieces of solid silver jeweler's wire, or silver coin.
Some cultivators claim that the genes responsible for hermaphroditism are present and may be expressed under stress from any of the above methods and that once expressed, this characteristic passes to seeds regardless of what activated it. This view, in large part, is incorrect, as a random half of the genes present in each of the parental plants passes to the next generation, regardless of whether the genes that contribute to hermaphroditism were induced by stressors or not. This widely accepted Mendelian model of inheritance (Mendelian inheritance) does allow for genetic mutations that have occurred in the germline (Germline) of an organism to be passed on to any offspring, but this process applies to all DNA sequences, not just those contributing to hermaphroditism. The inheritance of acquired characteristics (Lamarckism) that are not directly coded in the DNA sequence (Epigenetics) has recently received much attention in the area of genetic research and could possibly explain any anecdotal evidence for increased hermaphroditism in the offspring of plants induced to a hermaphroditic state. However, a more likely explanation is that by propagating plants easily induced to hermaphroditism by environmental stressors, the frequency of genetic elements contributing to this trait is increased by artificial selection following traditional genetic models of inheritance. Some theories suggest it is possible to selectively breed hermaphroditic cannabis to express the female flowering before the male flowering occurs, though this kind of selective breeding is beyond the capabilities of most cultivators.
When crossing two strains of cannabis (or two of any plant), the resultant hybrid may possess what is called hybrid vigor. In general, this produces a plant that is healthier, stronger, or quicker growing than its predecessors. Sometimes, in the case of a plant that has been brought back from fruiting (fruition, as mentioned above), it may be beneficial to cross it back with another (close) relative, in the hopes that it becomes invigorated.
Caution should be exercised, as one does not always attain a beneficial cross with hybridizing.
Vegetative propagation (cloning)
Like most plants, cannabis has the potential for vegetative propagation, with the most common and simple method being cutting. Cutting is characterized as a cloning method, since the derived plants have identical DNA to the "mother plants".
Under appropriate environmental conditions, a cut part of the cannabis plant, typically from the main stem or a lateral branch, has the ability to produce roots and develop into a whole new plant (the clone), genetically identical to the mother. In cannabis, the production of roots may take anywhere from 5 to 21 days.
The oldest method of cannabis propagation is water cloning. Used for nearly as long as agriculture has been a part of human development, one simply sticks the cut end of clone (cutting) into a small body of water like a glass or bowl and waits. Water cloning can take longer to show roots, but is a truly natural way to propagate any plant that is able.
Marijuana growers often root clones in peat pellets (compressed peat moss) or in rock wool. Another technique that has become popular for rooting clones is aeroponic cloning.
The main steps of hormonal cannabis cutting are as follows:
- Part of the main stem or lateral branch up to 20 cm long is dissected in a non-vertical manner. The bottom 2/3 of leaves are removed.
- The cut end is brought to contact with rooting hormone, according to instructions, to promote root growth and inhibit fungal infection.
- The cutting is placed in an appropriate initial medium such as common soil, compost, perlite, vermiculite, peat moss, sand, rock wool, oasis foam or a combination of those. The initial medium is kept moist and high humidity is maintained in the surrounding air. Elevated humidity levels slow the transpiration rate (water loss from leaves) and prevent the cutting from drying out. Mold is a common hazard due to the higher humidity and stressed cutting. During this phase, the temperature is kept relatively low (25 °C (77 °F)) and direct light is avoided so that the cutting does not dry out. The production from the slower photosynthesis is put into root production.
- After initial root development is evident (usually within three weeks) the cutting is ready to be transplanted into its final grow medium. The high humidity environment is no longer necessary.
Prior to the establishment of the first legal cannabis market in Colorado, United States, growers of the plant in the American State of Washington experimented with the use of cannabis waste for pig food. In early 2013, potent cannabis waste products were mixed into the feed of four pigs during the last four months of their lives, resulting in a weight increase of 20 pounds (9.1 kg) to 30 pounds (14 kg) that was registered before the pigs were sent to slaughter in March 2013. Washington State's draft regulations prescribe that cannabis waste must be "rendered unusable prior to leaving a licensed producer or processor's facility," and adds that mixing it with food waste is acceptable. The European Food Safety Authority reported in 2011 that "no studies concerning tolerance or effects of graded levels of THC in food-producing animals have been found in literature." The agency also noted that "no data are available concerning the likely transfer of THC ... to animal tissues and eggs following repeated administration."
- Cannabis strains
- Autoflowering cannabis
- Grow house
- Legality of cannabis
- Medical cannabis
- Organic farming
- Vertical farming
- Cannabis sativa L. – Encyclopedia of Life. Eol.org. Retrieved on 7 August 2011.
- American Journal of Botany (2004). "A chemo taxonomic analysis of cannibalized variation in Cannabis (Cannabaceae)". American Journal of Botany 91 (6): 966–975. doi:10.3732/ajb.91.6.966. PMID 21653452. Retrieved 8 October 2006.
- Small, Ernest (1975). "American law and the species problem in Cannabis: Science and semantics". Archived from the original on 19 April 2005. Retrieved 8 October 2006.
- Greg Green (2001). The Cannabis Grow Bible (4th ed.). p. 47. ISBN 1-931160-17-1.
- Jorge Cervantes. Marijuana Horticulture (5th ed.). ISBN 1-878823-17-5.
- The Marijuana Grower's Guide (1998) by Mel Frank and Ed Rosenthal, typed by Ben Dawson, revised 1992
- The inheritance of chemical phenotype in Cannabis sativaL. (III): variation in cannabichromene proportion E. P. M. de Meijer, K. M. Hammond, M. Micheler. Received: 21 April 2008 / Accepted: 7 August 2008 / Published online: 23 August 2008, Springer Science+Business Media B.V. 2008 development
- "Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 153,154
- "Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 164
- "Male Vs Female Marijuana Plants? Pics & Difference". Mary Jane's GARDEN. maryjanesgarden.com. 14 November 2001. Retrieved 3 May 2014.
- "Marijuana found growing in trees". abc27.com. 2010.
- toon (1 July 2008). "Cannabis Growing Guide Part 2 – Grow lamps". A1b2c3.com. Retrieved 16 March 2009.
- "Growing Tips". HG. Retrieved 20 February 2015.
A study published in Proceedings of the National Academy of Sciences, performed by a team of scientists at Duke University, discusses the effects CO2 has on every day plants found in the forest. One plant they chose for in-deph alaysis was poison ivy. The team conducted the study over a 6 year period at the Free Air Carbon Dioxide Enrichment (FACE) in Duke Forest. They dispersed carbon dioxide into a set of outdoor environments, to mimick levels similar to those they predict for our global atmosphere in 2050. The results were, compared to plants in the the control environments (natural atmosphere), poison ivy in CO2 enriched areas grew 149% faster, and produced 153% more urishol (the toxic resinous ingredient that causes rashes)!
- Rosenthal, Ed. "Temperature, Humidity & Air Quality". Retrieved 20 February 2015.
When CO2 is being used, the plant prefers to be a few degrees warmer, between 79° and 85° F (26°-29° C).
- "Houses suffer damage from grow-op activities". The StarPhoenix (Saskatoon). Retrieved 28 April 2011.
- Harvey, Ian (May 2005). "Grow Ops—An Inside Look". Reader's Digest. Archived from the original on 15 April 2005. Retrieved 28 April 2011.
- Niagara Region Police Service Marijuana Home Grow Operations. Nrps.com (2009-01-01). Retrieved on 21 November 2014.
- Goddard, John (22 December 2009). "Real estate agent jailed, fined M for grow-op scheme". The Star (Toronto). Retrieved 28 April 2010.
- Small, Peter (5 May 2009). "Grow-op king duped 54 homeowners". The Star (Toronto). Retrieved 28 April 2010.
- "Grow Op Cover Up". CBC News.
- Ready – Set – Grow (High Times Marijuana Growing Instructional Video)
- "Cannabis and Cannabis Extracts: Greater Than the Sum of Their Parts?". haworthpress.com.
- Jonathan Kaminsky (20 May 2013). "Marijuana waste helps turn pot-eating pigs into tasty pork roast". Reuters. Retrieved 26 May 2013.
- Cervantes, Jorge (2001). Indoor Marijuana Horticulture. Van Patten Publishing. ISBN 1-878823-29-9.
- Cervantes, Jorge (2006). Marijuana Horticulture: The Indoor/outdoor Medical Grower's Bible. Van Patten Publishing. ISBN 1-878823-23-X.
- Clarke, Robert Connell (1981). Marijuana Botany. Berkeley: Ronin Publishing. ISBN 0-914171-78-X.
- Green, Greg (2003). The Cannabis Grow Bible. San Francisco: Green Candy Press. ISBN 1-931160-17-1.
- Herer, Jack (1998). The Emperor Wears No Clothes. Ah Ha Publishing. ISBN 1-878125-02-8.
- Starks, Michael (1990). Marijuana Chemistry: Genetics, Processing & Potency. Ronin Publishing. ISBN 0-914171-39-9.
|Wikibooks has a book on the topic of: Marijuana Cultivation|
- A commercial marijuana landlord
- Marijuana Farms: A Primer – slideshow by Life magazine
- Cannabis cultivation at DMOZ