Cannabis cultivation

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Typical home-grown organic sinsemilla bud compared to a cigarette pack.

This article deals with the cultivation of the flowering plant cannabis primarily for the production and consumption of marijuana buds, which contain the main psychoactive ingredient tetrahydrocannabinol or THC. Cultivation techniques for other purposes such as the production of hemp vary dramatically. A basic description of hemp cultivation can be seen in the US propaganda film Hemp for Victory, shot during WWII. While it is possible to grow cannabis simply for the purpose of a houseplant or as a hobby, the practice is quite challenging due to the need to keep the annual plant in a near perpetual vegetative state, which requires root pruning and artificial lighting for the winter months.


General aspects

Brief History

Evidence found in ancient burial sites indicates that humans have been experimenting with cannabis recreationally, spiritually and medicinally since the 3rd millenium BC.[1] Herodotus, an important Greek historian of the 5th century BC, described how the Scythians of the Middle East used cannabis in steam baths.[2] The status of cannabis has changed in recent years. In 1937 the USA outlawed cannabis for reasons possibly related to racism and/or industrial economic interests.[3] In the 2000s, the vast majority of states has outlawed the cultivation, consumption and trade of cannabis with penalties ranging from a small fine to jail time.[4][5]


Autoflowering hybrid auto AK47 during flowering stage

Cannabis belongs to the genus Cannabis in the family Cannabaceae, along with hops. It comprises three species: C. sativa, C. indica, C. ruderalis (APG II system)[6] and is usually a Monecious (has separate pistillate (female) and stamenate (male) plants) annual plant (life period: April-September).[7][8][9]

Generally only non-drug cultivars of C. ruderalis are grown for industrial/agricultural purposes whereas for consumption high-cannabinoid cultivars of both C. indica and C. sativa can be used. C. sativa generally grows tall (some varieties can reach 3 meters) and is possible to grow in a very close matrix. The resultant plants (often referred to as hemp) will have very fine yet strong fibers which can be used among many others for the creation of durable fine cloth resembling silk. C. ruderalis bears great differences relative to C. sativa and C. indica. It's very short, produces only traces of THC and flowers independently of the photoperiod and according to age. The other two species flower as they sense light hours diminishing due to forthcoming winter.[10] However, commercial cross-bred hybrids containing both ruderalis, indica and/or sativa genes exist (usually called autoflowering). Such strains are advantageous for some growers due to their small size and early harvests. The lowrider can be harvested within 60 days from germination.[11] See also: Cannabis strains.

Cannabis needs five things to prosper: A grow medium (like soil), light (natural or artificial), warmth, water and nutrients (food).

Air Temperature

Cannabis is a summer plant. The optimal day temperature range for cannabis is believed to be 24 to 30 °C. At night temperature may fall as low as 15.5 °C. Temperatures above 31 °C and below 15.5 °C seem to decrease THC potency and slow growth. At 13 °C a plant will undergo a mild shock, though sometimes cannabis has been observed to withstand (only temporarily) freezing temperatures.[10][12][13]


Soil is the natural growing medium of cannabis and very popular among growers. Certain characteristics are recommended:

  • Good drainage to facilitate nutrient absorption and prevent root drowning.
  • Ideal pH between 6.0 and 7.0. To increase pH one can add agricultural lime during watering. For decrease ground coffee or lemon peels may be used. Commercial fertilizers (even organic) almost always make the soil more acidic (decrease its pH).
  • Ideal temperature range: 18-24 C.
  • Fertilization: NPK stands for the percentage of Nitrogen, Phosphorus and Potassium respectively, the most essential elements a plant needs to thrive. NPK shows the degree of fertilization in commercial soils. For example if a bag of soil reads "N-P-K: 12-12-12" this means 12% N, 12% P, 12% K. Proper soil for cannabis must contain all three in both stages of growth, with more N required for the vegetative stage and more P for the flowering stage. A vegetative fertilizer may say 3-1-1 or 30-10-10. A flowering fertilizer may say 1-3-1 or 10-30-10. There are wide choices of chemical fertilizer NPK ratios available commercially.

Loam soil and compost are considered most effective and cheap choices.

[10] [12]


Watering frequency indoors is determined by many factors, including the age of the plant, the stage of growth, the medium used, the medium's makeup, the grow room's temperature, the light used and container volume. It is not possible to recommend a specific interval good for all plants in all stages of growth. A very common way to determine when to water is to keep an empty planter filled with dry soil next to your plants. Compare the weights daily and do not let your plants get as light as your dry example.

A conspicuous sign of water problems is the downward wilting of leaves.[14]


Fertilizer burn on a leaf

Nutrients are the food of plants and come in the form of fertilizers which can be chemical or organic, liquid or powder and may contain several elements (see also: fertilizer). Commercial fertilizers must indicate the levels of NPK (mentioned above). During vegetative stage cannabis needs more amounts of N than of P,K while during flowering P is more essential than N, K. The presence of secondary nutrients (Calcium, Magnesium, Sulphur) is recommended. Also there are seven micronutrients (Iron, Boron, Chlorine, Manganese, Copper, Zinc, Molybdenum) that are not extremely important and rarely manifest as deficiencies.

Fertilizers although vital for good cannabis growth, must be used frugally otherwise they could burn the plant. As a general rule, half the amount suggested in a bottle may be given each time.[15]

As a plant acclimatized to virtually every growing region on Earth, its nutrient needs vary widely with its genetics and can truly only be determined with experience. Chemical plant foods vary greatly maker to maker, and some can be used at full strength, or the strength listed for plants with large fruits like the tomato.

Organic cannabis

Organic cultivation of marijuana is similar to the organic food movement in recent times. It is superficially similar to the hydroponic methods, with the exception of tending towards soil and nutrients which are derived from organic sources. In general, these sources are items like guano. The use of soil (generally in buckets or ally printed on the container. For this reason, the supposed organic cultivation of cannabis, especially indoors, resembles other controlled cultivation methods where the intake of the plants is closely monitored.

Stages Of Development


File:Indica seeds.JPG
C. indica seeds

Duration: 12 hours to 8 days. Warmth, darkness and moisture initiate metabolic processes such as the activation of hormones which in turn trigger the expansion of the embryo within the seed. Then the coating cracks open and produces a small embryonic root that begins growing downwards due to 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, as the remains of the seed shell are pushed away. This marks the beginning of the seedling stage.

Seeds may be germinated by soaking them between wet paper towels, in a cup of water at room temperature for 24 hours, or in wet peat pellets. Regardless of the method used however, distilled water is often employed since it has the proper pH. In most cases tap water is sufficient. Peat pellets are often used as a germinating medium as they make it unnecessary to transplant the fragile seedlings; the saturated pellets with their seedlings can be planted directly into the intended growing medium with a minimum of trouble and effort, or shock to the plant.

A technique that achieves high germination rates is the following: First the seeds are inserted into a cup of water. All will initially flow over the surface so forcing them to immerse completely is recommended. Then the cup is left in a warm dark place for no more than 24 hours (otherwise seeds might drown). Shortly most will go down the bottom, an indicator that water has penetrated the shell. Finally, the seeds are placed carefully in a constantly damp, warm and dark environment such as wet cotton or towel. Dirty hands (even traces of nicotine on them) can damage the seeds. As soon as the root can be distinctly seen, the seeds are ready to be placed in a growing medium.

Seedling phase

A very young C. sativa seedling. The tips of the first two true leaves are emerging between the two round seed leaves (cotyledons)

Duration: 1–4 weeks. The seedling stage begins when the seed breaks and exposes its round “seed leaves” or cotyledons. This is the most fragile time during the entire life cycle of the cannabis plant. It is important to keep a constant atmosphere with a high humidity level and medium to high light intensity. Most indoor growers use compact fluorescents or T5 fluorescents during this stage as they give off little heat. HPS and MH lights give off large amounts of radiant heat and increase the rate of transpiration in the plant. Seedlings have small root systems and can dry out very quickly, thus keeping the medium moist is important.

The plant can begin to sex itself in this stage but if time is an issue one can induce sexing by switching to a 12/12 hour period. Once sex is determined you can remove the males and switch the cycle back to vegetation stage by inducing an 18/6 hour period.

Vegetative phase

A young male cannabis plant during early flowering stage

Duration: 1–2 months indoors. In this stage the plant needs all the light (at least 18 hours) and nutrients (food) it can get. It will continue to grow upwards and produce new leaves. The sex is starting to reveal 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 (autoflowering hybrids) omit the vegetative stage and pass directly from seedling to pre-flowering.

When the plant possesses 4 sets of true leafs and the 5th is barely visible in the center of the growth tip, or shoot apical maristem (SAM), the plant has entered the vegetative phase of growth. During the vegetative phase of growth, the plant directs its energy resources primarily to the growth of leaves, stems, and roots. A strong root system is imperative, as it 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. The males are then culled when they are identified, because they don't produce buds or flowers. If males are allowed to pollinate the females their potency will be greatly reduced, as energy that would have been used to make large, potent buds instead goes to making seeds.[16]

During the vegetative phase of growth, cultivators generally employ an 18 to 24 hour photoperiod, as the plants grow more quickly if they receive more light, although a warmer and cooler period are required for optimal health. While 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.

The amount of time to grow a cannabis plant indoors in the vegetative stage depends on the size of the flower light you use, the size of the space you're flowering in and how many plants you wish to flower at once and how big your strain gets in 'the stretch' - the first two weeks of flowering.

Marijuana cultivators employ fertilizers high in nitrogen and potassium during this stage, as well as a complete micronutrient 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 in order to encourage shorter plants and denser canopy growth. For example, unless the crop is too large to be extensively pruned, cultivators will 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:


Is done by removing the top of the apical meristem (dominant central stem), called the apex or terminal bud, in order 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 almost infinitely, but over-diffusion of apical dominance will produce 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 supercropping) is similar to topping in that it causes the lower branches to grow more rapidly, but the apical meristem will 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 will cause the lower limbs to grow more rapidly while the pinched tissue heals, after which time the stem will resume apical dominance.


LST stands for Low Stress Training and is another form of supercropping, many times referred too as LST supercropping. 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) LSTing can be used to keep all growth tips (meristem) 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 LSTing. LSTing works by changing the distribution of hormones, more specifically Auxins, in the plant. Low Stress Training was introduced in 2001 by member Delta9420 at the website (known then as

Pre-flowering phase

Duration: 1 day to 2 weeks. Also called 'the stretch'. In most plants will last for 10–14 days after switching the light cycle to 12/12. The plant development increases dramatically, with the plant doubling in size or more (see reproductive development below). The production of more branches and nodes occurs in this stage as the structure for flowering is built. The plant will start to show calyx which appear where the branches meet the stem (nodes). Pre-flowering indicates that the plant is ready to flower.

Reproductive/Flowering phase

The flowers of a male cannabis plant

Duration: 4–16 weeks. The sex is clearly revealed. Males produce little balls clustered together like grapes. Most plants (except autoflowering strains which flower independently of photoperiod) will flower under diminished light. In nature, cannabis plants sense the forthcoming winter as the earth turns and daylight reduces in duration (see also season). If females are not pollinated (fertilized by male pollen) they will start to produce buds containing sticky white resin glands or trichomes in a final attempt to attract male pollen (THC is very sticky and thus the plant produces more when it is not fertilized). The trichomes contain the largest amounts of THC and CBD, the two main psychoactive substances. Indoors, flowering is induced by keeping the plant in complete dark for 12 hours every day, until it is ready to be harvested. If manipulated, a female can either generate a seedless bud, a bud with a few seeds, or a bud that is almost totally seeds. The first case is achieved by removing all the male plants before any of their flowers open, the second occurs when one or more male flowers have barely burst open and then removed and the third case occurs if the males are let to fully pollinate the females.

Buds of the first case are called sinsemilla (it is really two words: "sin semilla," which translates to "without seeds" in Spanish, but is often misspelled as one word). The resultant cannabis contains the most Cannabinoids possible[citation needed]. The amount of Cannabinoids in sinsemilla is considerably more in comparison to cannabis that has been grown in a pollinated environment, because the production of seeds requires an immense amount of energy, and if left unpollinated a female plant will divert all her energy to calyx production in an effort to seize pollen.[citation needed] This is especially desirable, as the calyx is where the highest concentration of trichomes exists, and the more densely packed a plant is with calyces, the greater psychoactive effect that plant will likely have. Potent sinsemilla is especially important to medical users, to minimize the amount of cannabis they must consume in order to be afforded relief. Cannabis with seeds is generally considered to be of inferior quality and/or grown with inferior technique. Common terms for seeded, or otherwise low-quality, cannabis are "mids," schwag, "regs," "booty,", "greta" or mersh.

Indoors, plants like cannabis are induced into flowering by decreasing its photoperiod to at least 10 hours of darkness per day. Traditionally most growers change their plants lighting cycle to 12 hours on and 12 hours off. 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 come fall and winter.[17]

While 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 flower with 12 hours of darkness to be safe. The flowering hormone is very quickly inhibited, taking less than two minutes of exposure.

Flowering usually lasts from 45 to 90 days indoors. If growing outdoors it may take somewhat longer, depending on the natural onset of the colder seasons. The flowering length is mainly genetically determined with plants (as pure cannabis "indica" strains) flowering in as low as 45 days, while plants (as cannabis "sativa") can take up to 4 months to finish and the harvest yields significantly less. This is also the main reason why certain plants (as cannabis indica) are almost always grown indoors (unlike cannabis sativa, which is also grown outdoors).

Some plants, specifically members of the subspecies Ruderalis, will begin the flowering cycle without a significant reduction in their photoperiod.

Flowers from certain plants (eg cannabis) are called Calyx, and are (with cannabis) the most prized part of the plant. In late flowering the calyx are easily visible to the naked eye. Calyx 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. Calyx development ends around 5 weeks into flowering and is proceeded by a period of Calyx “swelling”. During this time the buds greatly increase in weight and size.

[10] [12]

Outdoor Cannabis Cultivation

File:Guerrilla Cannabis.jpg
Guerrilla cannabis plot in a forest clearing
Aerial view of guerrilla cannabis plot
A chart demonstrating the reflective qualities of cannabis in comparison with other common plants, which may be used for cover.

Cannabis can be planted outdoors under the sun, either on natural soil or in pots of pre-made or commercial soil. 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, with outdoor cultivators tending to grow indica-based strains due to their heavy yields, quick maturing time, and shortness. Some growers prefer sativa because of its clear-headed (cerebral) high, better response to sunlight, and lower odor emissions.

One can cultivate on his own property or practice guerrilla farming i.e. plant cannabis in remote areas such as forest clearings or mountain cliffs and visit rarely. However such a method is prone to ripoffs - so much so that some ingenious growers even attach pots on trees to decrease this possibility.[citation needed]

When cultivated outdoors, the chosen areas are those which receive twelve hours or more of sunlight in a given day. In the Northern Hemisphere cannabis seeds are typically planted in late May or early June, so the plants can have a full four months of growth. Typically, the plants are harvested anywhere from mid September to early October. In North America, northern locations are preferred (Humboldt County, California and British Columbia being particularly notable), but southern locations (such as Maui, Hawaii) are also known to be good producers.[citation needed]

In instances where the local laws do not permit growing cannabis, cultivators may choose to grow in forests or rugged and rural areas where the local population are not likely to find the crop. Another technique is to grow cannabis in a crop that is larger and obscures the plants, such as maize. This is reported by the United States government to be common in the midwestern states.[citation needed] Bamboo and elderberry are also used as camouflage companion plants.[citation needed]

Some government organizations have claimed that in state and national parks, people have been injured by "rebel farmers" protecting their crops, including a well documented developing problem with Mexican cartels growing cannabis in US national parks and forests.[citation needed]


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 dig a hole and put a potted plant in it. This can reduce a plant's height by at least a foot, reducing visibility to neighbours, visitors and guests. Also, some growers top the plant when it is only 12 inches (30 cm) high, and grow the 2 tops horizontally along a trellis. When using this technique, it is unlikely the plant will grow to be over 3 feet (1 m) tall.

Law enforcement agencies often monitor certain wider areas, particularly areas of countryside with a significant history of outdoor cannabis cultivation. In helicopters, they use infrared cameras and other equipment that can detect cannabis by measuring the heat and reflective signature of the vegetation below. Cannabis has higher reflectivity at certain wavelengths than other rural crops, such as corn. Law enforcement agencies have found that the use of this technology has become necessary in their detection efforts because many growers hide cannabis among other plants, making detection with the naked eye difficult even from the air. These techniques are effective and difficult to defeat because a plant's reflective signature is difficult to change or mask. It has been saidTemplate:Who that if the cannabis plant is planted by a pine or cedar tree the heat from the tree will overlap the cannabis plant heat making it harder to detect from helicopters.

Indoor Cannabis Cultivation

Indoor Cannabis cultivation.

Cultivating Cannabis indoors traditionally has to do with growing the plants in a soil-like medium and adding fertilizer when the plants are given water. Cultivating marijuana indoors is more complicated and expensive than growing outdoors, but it allows the cultivator complete control over the growing environment. Cannabis grown outdoors can be just as potent as its indoor counterpart if tended to properly.

Cultivating plants indoors can also be done through the use of hydroponics; however, this method is somewhat less common.[18][19]

In order to grow plants indoors, a growing medium (eg soil or growing substrate), water, nutrients, light and air need to be supplied to the plant.

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 needs to be imitated.[20] For example vegetables grow best in full sunlight, which means in practice that as much light as possible must be supplied to grow cannabis indoors (high intensity discharge (HID) lights such as high pressure sodium (HPS)and metal halide (MH) are preferred. fluorescent lamps can also be used). Incandescents and mercury vapor lighting are not used in cannabis cultivation.

In addition, plants also require both dark and light ("photo"-) periods. As such, lights need to be timed to switch them on and off at set intervals. The optimum photo/dark-periods is specific depending on each plant (some prefer long days and short nights an others preferring the opposite, or something in between)

Most plants will grow under most light spectra, yet always prefer a full spectrum light. A test done by Ed Rosenthal[citation needed] 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 vegetative phase of growth, as it encourages short internodes (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 as cannabis the amount of working substances as THC) produced by the plant. High pressure sodium lamps trigger a greater flowering response in the plant and are thus used for the second (or reproductive) phase of the growth, or they are used by those people who only wish to purchase 1 single lamp.[21] If high pressure sodium lamps are used for the vegetative phase, plants will usually grow slightly more quickly, but will also have longer internodes, and may be taller.[22]

Recent advancements in LED technology have allowed for diodes that emit enough energy for cannabis cultivation. While LED grow lights have been in production for many years, they have only recently been able to produce yields that approach those of a 1000w HPS lights.

In 1996, Graham Reinders, author of the celebrated book How to Super Charge your Garden wrote, referring to a 1000watt High Pressure Sodium light, “It has an enormous lumen output, but not a very good PAR output because most of its light is at the wrong frequency for plants. The bulb has most of the light spectrum in the “orange” range, with almost no ‘blue’ and very little ‘red.’ For this reason, it is poor in the 430-460 nm, and poor in the 680 - 700 nm. Luckily, the light is so powerful that the spill -over at these frequencies is still sufficient to do a good job.” Thirteen years later, innovative people have taken this principal shortcoming of the HPS and turned it into an advantage for LEDs. LED lights allow one to focus intensity in the high PAR absorption range of the light spectrum. New models of LED grow lights incorporate multiple types of chips that cover the whole range of red light, blue light, and now full spectrum light.

One major short coming of LED’s in the past has been a lack of intensity. Higher wattage chips are required to produce enough luminous efficiency to produce larger, denser yields. As with using a 400w HPS vs. a 1000w HPS, intensity has everything to do with yield. The same applies to LEDs however, it is not as simple as measuring watts because better quality chips can produce more light with less watts than cheap chips running at lower watts.

LED grow lights have become an accepted technology in cannabis cultivation. However, the market remains flooded with cheap quality LED lights that do not produce yields comparable to what growers are accustomed to. Many companies are using single watt LED chips, which have notoriously produced low yields and wispy results. Growers should look for lights with 2 watt chips or higher. When considering purchasing LED grow lights, one should carefully examine both the spectrum and the intensity of the light.

The advantages of LEDs, low electrical draw, low heat output, long life span, and simpler environmental control, coupled with the ever increasing quality of the technology ensure that they are here to stay and potentially to mark a significant transformation in the cultivation of cannabis.

File:LED panel and plants.jpg
LED panel light source used in an experiment on plant growth by NASA. Pictured plant is a potato plant.

According to the inverse square law, the intensity of light radiating from a point source (in this case a bulb) is inversely proportional to the square of the distance from the source. So if an object is twice as far away, it receives only 1/4 the light. This is a serious hurdle for indoor marijuana growers, and many techniques are employed to use light as efficiently as possible.

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 wind up on the plants (rather than partly besides it). Often, the distance between lamp and plant is in the range of 0.6 m ft 0 with incandescent lamps, to 10 cm in 0 with other lamps, such as compact, large and high-output fluorescent lamps. Some marijuana cultivators cover the walls of their grow-room with some type of reflective material, or alternatively, white paint to maximise efficiency.

One commonly used covering is 6 millimeter (150 µm) PVC plastic sheeting that is white on one side and black on the other. The plastic is installed with the white side facing in to 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. Mylar sheeting from a grow store is 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 in order for the plants to grow most 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 will grow more quickly, have larger stomata, and can utilize more light. 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 hereby emitting CO2), a baking soda and vinegar mixture in a container, or dry ice.[23]

Certain plants (eg 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. 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.


Indoor cannabis plant during flowering

Indoor growing has become increasingly common over the past decade, in part due to 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 in which 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 marijuana. More expansive grow-ops, however, are generally more susceptible to detection than smaller operations.

Since individual grow light power generally ranges from 250 watts to in excess of 1000 watts and remains 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 witness significant increases in power usage relative to a household's previous electricity costs. 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 (eg 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 in conjunction with ventilation in order to control odors. This typically involves forcing air from the grow room through a device containing activated carbon, before being vented 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 the grower and the plant. As a last resort, strong air fresheners are used to control smells as well as keeping windows firmly shut. This is a risky method, as the smell of air fresheners may often arouse suspicion by police officers. 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 which possesses a weaker odor.

Storing plants and lights away from windows and areas which may be seen by visitors is also a common practice, as is keeping the entire grow op in an attic or basement. Some growers, finding this impractical, may cover their windows with light-resistant materials. This can solve the problem of escaping bright light but may arouse suspicion amongst neighbours and local residents.

Many cultivators face detection by fire. Fires normally originate from faulty electrical equipment or wiring. Shoddy fixtures and sockets, improperly grounded equipment, and faulty circuit breakers are some of the most prevalent causes. Due to the large amount of electricity needed for large-scale cultivation, old or damaged wiring is prone to melt and short. Some commercial growers resort to power theft in order to hide electricity usage and many do not take precautions to ensure that their connections are 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 of course 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 reticent to talk about their cultivation.

Housing Damage

[24] Houses used as grow-ops are exteriorly maintained in their normal fashion. However the interiors may have received significant structural, electrical and heating system modifications not in accordance 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 are made to replicate warm, humid climates in which hybrid plants flourish to produce high potency marihuana. Houses used as grow-ops can suffer considerable structural damage, as a result of moisture and toxic mold.[25]

One of the largest such examples was masterminded by a Markham, Ontario real estate agent who turned 54 rented houses into grow-ops. Hydro companies estimated the value of the electricity stolen and insisted that homeowners pay before hooking them up again.[26][27]

Harvesting, drying and curing

Close-up of a female marijuana bud in flowering stage. White trichomes can be seen coating the surface, which will darken as flowering progresses.

A typical indicator that a plant is ready to be harvested is when 2/3 of the pistils have turned from white to reddish brown or other color. In general, harvesting consists of drying and curing. Curing is essential for the even distribution of moisture in the buds. A popular alternate method is the following:

  1. Dry: Buds left in well ventilated dark place for 24 hours
  2. Cure: Buds stored in sealed bag and left in dark place for 8 hours
  3. Dry: Buds left in well ventilated dark place for 16 hours
  4. Cure: Buds stored in sealed bag and left in dark place for 6 hours
  5. Dry: Buds left in well ventilated dark place for 12 hours
  6. Steps continued likewise as necessary

In 3–4 days buds are ready for consumption. [28]

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, "crystals", barely begin to turn milky from clear. These trichomes can range from completely clear (generally deemed underdeveloped), to amberish-red. Ideally, professionals will 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 will swell to form full "colas" (Spanish for "tails"). If harvested early on with only a few of the pistils turned color, the buds will have a more pure THC content and less of the cannabinoids CBD and CBN. The latter cannabinoids are non-psychoactive; they contribute to the bouquet of the marijuana and modulate the overall nature of the high anywhere from purely psychedelic to purely sedative.

Contrary to sinsemilla (bud production focused cultivation), seeds are harvested when fully developed and often after the accompanying buds have begun to deteriorate. In contrast, hemp grown for fiber is harvested before flowering, and cannabis grown for cloning is not flowered at all.


The plants are dried at room temperature in a dark space. 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. A stable temperature preserves cannabinoids well. Some believe flowers are 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. When the stems in the middle of the largest buds can be snapped easily, the plant is dry enough to be cured. Drying is done in a dark place, as THC resins will deteriorate if exposed to light and the degradation product CBN will be formed, thus significantly altering the cannabinoid profile of the dried flowers.


The curing process continues breaking down sugars and helps develop taste and smoothness of smoke. Usually, the dried product is packed (not compressed) into glass canning jars which are airtight. Initially the product is checked periodically (every few hours) to make sure it was properly dried and has not remoistened 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.

A recent method of curing is called water curing. This method is quicker and can improve a lower quality product. The freshly cut buds are submersed in water for a period of 7 straight days, changing the water daily. The buds are then dried and are ready to use. Nutrients can be added to the plants up until they are harvested. When water curing, the water will flush out harmful chemicals (such as the ones used to feed the plants) as well as proteins, sugars, pigments, chlorophyll and some resins. This will also increase the THC to weight ratio.[29] Many believe the finished product is not as attractive as using a standard dry and cure

Tincture. Ethanol is used to extract cannabinoids from the marijuana plant (THC is soluble in alcohol). The extraction process takes longer, but results in an edible product. Marijuana 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 (THC vaporizes at 180°C). Smokers usually heat the liquid and inhale the vapors through a straw.


Main article: Hashish

Hashish can be expensive but like everything else in cannabis cultivation, it can be an investment that pays for itself. After a harvest, there are typically many green leaves- particularly large shade leaves- which themselves cannot be smoked, but have collected over time many fallen trichomes. Rather than letting them go to waste, these are soaked in a bucket of cold water. The liquid is then passed through a succession of bags with decreasing screen sizes which capture the trichromes, which are then pressed into shape and let dry. The result is called bubble hash, due to the bubbling which occurs when it is heated for smoking. This bubbling is due to its purity, as adulterants tend to cause hash not to bubble.[30]

Hash Oil. Allowing the ethanol in a tincture to evaporate makes hash oil. **Ethanol should never be evaporated with direct heat, or near an open flame!** The resultant hash oil is often very strong in terms of THC content (depending on parent material), and can be then smoked. Delta 9 THC is most strongly soluble in petroleum ether and less so in ethanol. Adding petroleum ether to tincture will extract D9 THC, and leave water soluble chemicals in the ethanol (certain cannabinoids, proteins, chlorophyll, etc). Hash oil purified this way can exceed 90% D9 THC.

Pests And Insects

Outdoor growers are more likely to have problems caused by pests. If these need to be treated with chemicals only pesticides and insecticides which are safe to use on food crops should be used. Popular and safe pesticides include:

  • Pyrethrins: Organic and very effective, although sometimes hard to find and expensive due to high production cost.
  • Azadirachtin: Meeting most criteria to be classified as a natural instecticide. Biodegradable, non-toxic to mammals. Cheap and easier to find.

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

The legal status of cannabis has led growers to implement novel cultivation methods for indoor growing which involves the use of lamps, in order to avoid aerial surveillance of outdoor plots.[31] These methods include:

  1. using a water or air-based growth medium (known as hydroponics and aeroponics respectively)
  2. the use of homemade, organic composted fertilizers
  3. training and trellising techniques such as Screen of Green (also known as SCROG), Sea of Green (also known as SOG) "Supercropping" and LST supercropping; 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 1gram per watt 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. However, the individual plants grown with this method typically give smaller yields than those grown with other methods.[citation needed]


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 is initiated, the flower tips will reach through the wire and all be at relatively equal distances from the light source.

Light Depreciation: The Inverse Square Law [32] states, as the distance from the light source is doubled, the light intensity is quartered. Cannabis growers realize this and want to get the maximum use for their lights. With an untrained plant the lower branches of their plants don't produce as well as the upper branches, being too far from the light. The SCROG method reduces this problem by putting basically the whole plant on one vertical plane, allowing all bud sites to receive nearly maximum light. This is beneficial because it produces more by getting light where the plant needs it.Vegetative State: The plant should remain in the vegetative state until 70 to 80 percent of the net is full[33] As a branch reaches three to four inches above the wire it is pulled back under the wire and so trained to grow vertically until flowering. Due to 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.


Main article: Hydroponics
File:Hydroponic system-sloped Δ0067.JPG
An example for a small hydroponic system for cannabis cultivation

Hydroponic cultivation generally occurs indoors, although there is no practical obstacle to growing outdoors. In general, it consists of a non-soil medium which is 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.

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 fibre as a soilless medium due to its high drainage and buffering capabilities, making 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 and the Ecosystem 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 which maximizes the lumen output of the lights used.

Genetics and breeding

Selection of mother plants

An important factor in cannabis cultivation 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 (in the case of marijuana, one might use seeds from a batch that was particularly enjoyed), and then growing a number of the seeds to find out which exhibit the characteristics most desirable to the cultivator. These genetics should typically yield at least 1 gram per watt.

Plant characteristics which are generally selected for include:

  • Overall yield
  • Time to fruition
  • Resistance to pests
  • Geometric traits (uniformity, compactness, flower density, etc)
  • Color
  • Flavor and/or aroma
  • Appeal to end buyer (known as "bag appeal")
  • Psychoactive qualities
  • Trichome density and type (stalked or sessile)

When a cultivator has decided which plant or plants exhibit the most desirable traits, a cutting is taken and grown to maturity but never allowed to flower. This plant is referred to as a mother, and can be kept for years, producing thousands of clones genetically identical to the mother.[34]

Feminized seeds

It is possible to use a combination of cloning and "shocking" plants to get them to produce feminized seeds.[35] A clone will retain the same sex throughout its life, so if a female plant is cloned, its clones will also be female, precluding reproduction.

Some claim (particularly vendors of feminized seeds produced with certain methods) that while environmental stresses have been used to create pollen bearing male flowers on female plants- known as 'hermaphroditing' or 'hermying', this method is not preferred when creating feminized seeds; due to those plants most likely to revert to seed making being the ones which hermie soonest; hence passing on the genetic trait of instability of gender - desirable in the wild but not in cultivation.

Spraying selected leaves, branches and in cases where large amount of seed desired whole plants with colloidal silver solution has become a preferred method since the colloidal silver suppresses ethylene production in bud sites, stimulating male characteristics. Gibberellic acid has been used frequently; but is harder to find than colloidal silver, which involves nothing more than a small wall d.c. power supply and two pieces of solid silver jeweler's wire, or 99.999% silver coin. A method used by organic growers and promulgated by the famous Cannabis breeder Soma, is called 'Rodelization', or letting unpollenated female plants live several weeks longer than the normal harvest time. In such plants a hermaphroditic trait will self express in effort to continue the genetic line; the fact this method utilizes auto hermaphroditic traits which could contribute to instability in a plant's genetics is offset by grower observations that the tendency to auto-switch sex is not great in plants grown from seeds made this way, and the fact that it occurs naturally without effort on the part of the cultivator.

However, other cultivators claim that the genes responsible for hermaphroditism are present and may be activated under stress from any of the above methods and that once activated can be passed to seeds regardless of how it was activated. Traditional theories of inheritance would not have allowed for the passing of genetic alterations an adult has acquired after birth (called Epigenetics) but there is evidence that when a gene is activated in a mother after her birth that expression can be passed on to her offspring.[36]

Hybrid vigor

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 which is healthier, stronger, or quicker growing than its predecessors. Sometimes, in the case of a plant which 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 will become invigorated.[37]

Caution should be exercised, as one does not always attain a beneficial cross with hybridizing.

Cloning from cuttings

Template:Howto Like many plants, cloning of cannabis is possible through a relatively simple process. The process itself is quite similar to the cloning of most other plants and involves rooting branch cuttings from donor ("mother") plants.[38]

There are many methods of cloning available, from store bought purpose built cloning machines to inserting a cutting in a cup of water and waiting for roots to grow. Most methods will take anywhere from 5 – 21 days. Certain strains of cannabis have proven harder to clone than others.

"Blueberry" marijuana cuttings waiting to be trimmed and re-cut.
Trimmed with stem re-cut at 45 degree angle below a node.

Rooting hormone gel or powder mixes are then applied to the cut to promote root growth and inhibit fungal infection. The cutting is then placed in a rooting medium which may be a soil mix or a soil-less medium. Typical soil-less media are Perlite, vermiculite, peat moss, sand, rock wool or Oasis foam. A good medium is one that drains well, holds moisture and air well also. Oxygen is important for healthy root growth.

The cuttings in their new medium should be kept at a constant temperature (around 78 F) and with high humidity. Elevated humidity levels can be achieved by use of a humidifier or a humidity dome. Elevated humidity levels slow the transpiration rate which is important because without a root system the water uptake is very slow; If the transpiration rate exceeds the uptake rate the cutting is losing water and will wilt and die.

Many growers use a humidity dome as they are very inexpensive, around $7, and are easy to use. Many others improvise domes with simple plastic baggies secured with rubber bands (even less expensive and equally easy to use). When using a humidity dome, the dome should be removed at least twice a day and the rooting clones should be fanned to prevent mold and to give them some air circulation. Alternatively, you can cut off the bottom of a clear 3-liter bottle and temporarily put it over a single plant. The cap can easily be removed a couple times a day to easily refreshen air.

New clones under improvised humidity domes.

The rooting medium should be kept moist and should never dry out.

During other stages of growth one is advised to allow the soil to dry out to allow the roots to get oxygen and to prevent root rot. Since cuttings do not have roots this is not of concern. What is of concern is that a cutting will dry out and die, which occurs very rapidly.

Light intensity should be very low during the rooting process. High light intensities will force the plant to focus on photosynthesis at the expense of rooting. Light intensity should be increased during the last week up to normal illumination levels.

Cuttings usually take 7–14 days to develop root systems. Drooping is common within the first week. Cuttings that have not regained rigidity after 7 days are weak and are culled by most growers. To speed the rooting process keep the cuttings at constant temperature. Allowing the parent plant to become mildly nitrogen deficient before the cutting is taken will also speed rooting.

If performed correctly, the cuttings should stay green during their rooting time, and condensation should appear on the plastic coverings for the cuttings, which indicates proper humidity. After 7 days, healthy cuttings will appear strong with leaves reaching upward. Yellowing leaf tips are a common indicator of successful rooting. Browning likely indicates too much sunlight, too little humidity, cutting rotting in sitting water, or unsanitary cloning conditions.

In recent years, stores selling hydroponic grow equipment began offering automated machines (i.e.: EZCloner, etc.) in which trimmed cuttings are placed and left alone for approximately two weeks. Anecdotal accounts from established growers indicate these automated machines have near 100% success rates. Unfortunately, the cost (more than $300 USD) is prohibitive for most people that grow at home for personal use.

See also



External links

Further reading

  • Cervantes, Jorge. Indoor Marijuana Horticulture. Van Patten Publishing, 2001. ISBN 1-878823-29-9
  • Cervantes, Jorge. Marijuana Horticulture: The Indoor/outdoor Medical Grower's Bible. Van Patten Publishing, 2006. ISBN 1-878823-23-X
  • Clarke, Robert Connell. Marijuana Botany. Berkeley: Ronin Publishing, 1981. ISBN 0-914171-78-X
  • Green, Greg. The Cannabis Grow Bible. San Francisco: Green Candy Press, 2003. ISBN 1-931160-17-1
  • Herer, Jack. The Emperor Wears No Clothes: The Authoritative Historical Record of Cannabis and the Conspiracy Against Marijuana. Ah Ha Publishingm/chapters.html Internet edition of The Emperor Wears No Clothes]
  • Starks, Michael. Marijuana Chemistry: Genetics, Processing & Potency. Ronin Publishing, 1990. ISBN 0914171399
  • Clarke, Robert Connell. Marijuana Botany. Berkeley: Ronin Publishing, 1981. ISBN 0-914171-78-X

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