Cannabis cultivation

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

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.

Evidence found in ancient burial sites indicate that humans have been experimenting with cannabis spiritually and medicinally since at least the 3rd millennium BC.^[1] Herodotus, an early Greek historian, described how the Scythians of the Middle East used cannabis in steam baths.^[2] The status of the plant has changed in recent years. In the early 20th century the US outlawed cultivation, consumption and trade of all cannabis species because of a mixture of reasons, including racism and business interests. Thereafter the vast majority of countries have followed a similar paradigm, imposing penalties that range from a small fine to incarceration and execution.^[3][4]

Botany

See also: Cannabis (drug)

A flowering cannabis plant.

Cannabis belongs to the genus Cannabis in the family Cannabaceae and includes three species, C. sativa, C. indica, and C. ruderalis (APG II system).^[5] It is typically a dioecious (each individual is either male or female) annual plant (life period: April–September).^[6][7][8]

C. sativa and C. indica generally grow tall (some varieties reach 4 m) and their females start the production of flowers rich in THC (1% to 29%) as the season changes from summer to autumn. C. ruderalis is very short, produces only trace amounts of THC and flowers independently of the photoperiod and according to age.^[9] However, commercial cross-bred hybrids containing both ruderalis, indica and/or sativa genes exist (usually called autoflowering), the "low rider" being the most famous. Auto-flowering cannabis strains are considered advantageous by some growers because of their discreet size, short growing periods, and the fact that they don't rely on a change in light schedule to determine when to flower.^[10] See also: cannabis strains.

Cultivation requirements

Cannabis needs certain conditions to flourish.

Growth medium

Soil is required, except for cannabis grown with hydroponics

• Sufficient nutrients—commercial soil bags 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 6.0 and 7.0. This value can be adjusted – see soil pH. Commercial fertilizers (even organic) almost always make the soil more acidic (decrease its pH).

Warmth

The optimal day temperature range for cannabis is 24 to 30 °C (75 to 86 F). Temperatures above 31 °C and below 15.5 °C seem to decrease THC potency and slow growth. At 13 °C the plant undergoes a mild shock, though some strains withstand frost temporarily.^[9][11][12]

Light

Light can be natural (outdoor growing) or artificial (indoor growing).

When artificial light is used, from the germination until the flowering stage, the plant typically remains under a regime of 16–20 hours of light and 4–8 hours of darkness, although the plant can use a full 24 hours of light without harm. It is worth noting that there is an ongoing debate over the importance of the "Dark Period". It has been proven 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, as well as lack of vigor, and an overall decrease in vascular development. There is no defined "flowering stage", unless you are discussing an auto-flowering variety. Typically, flowering is induced by changing the light schedule to 12/12, or 12 hours of light and 12 hours of darkness. Flowering in cannabis is triggered by a hormonal reaction within the plant that is set on by an increase in its dark cycle. In other words, a plant needs sufficient prolonged darkness for calyx development(flowering) to begin. Sativa generally takes as little as 8 hours of dark to begin flowering, whereas Indica can take up to 13.

Water

Watering frequency and amount is determined by many factors, including temperature and light, the age, size and stage of growth of the plant and the medium's texture. A conspicuous sign of water problems is the downward wilting of leaves.^[13] Too much water can kill young cannabis plants. Plants are occasionally sprayed with water to fend off under-watering in small steps.^[14]

Nutrients

Fertilizer burn on a leaf

Nutrients are the food of plants and come in the form of fertilizers that 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 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. Also there are seven micro nutrients (Iron, boron, chlorine, manganese, copper, zinc, molybdenum) that are not extremely important and rarely manifest as deficiencies.

Fertilizers are vital for good cannabis growth but must be used frugally to avoid burning the plant. As a general rule, half the amount suggested in a bottle may be given each time.^[15]

Because cannabis is 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.

Stages of development

Germination

C. indica seeds

Duration: 12 hours to 8 days. Warmth, darkness and moisture initiate metabolic processes such as the activation of hormones that triggers the expansion of the embryo within the seed. Then the coating cracks open and produces a small embryonic root that 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.

Seeds may be germinated by soaking them between wet paper towels, in a cup of water at room temperature for 24 hours, in wet peat pellets, or directly in potting soil. Regardless of the method used, distilled water is often employed because it has the proper pH. In most cases tap water is sufficient. Peat pellets are often used as a germinating medium because they make it unnecessary to transplant the fragile seedlings and 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, put seeds in a cup of water. All seeds initially float on the surface, so they must be forced to immerse completely. Then leave the cup in a lukewarm dark place for no more than 24 hours. (Otherwise the seeds could drown.) Shortly most will sink to the bottom, which indicates that water penetrated the shell. Finally, place the seeds in a constantly damp, lukewarm, dark environment, such as wet cotton or a towel. Dirty hands (even traces of nicotine on them) can damage seeds. As soon as the root appears, 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 moderate 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, so 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) 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 than males. The males tend to have fewer leaves near the top and females have more leaves surrounding the flowers.^[16] 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 photo period because the plants grow more quickly if they receive more light, although a warmer and cooler period are required for optimal health.^[17] 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.

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 done by removing 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 almost 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

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.

LSTing

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) 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. LSTing resembles the training of grape vines into their support lattices. Outdoor gardeners also employ training techniques to keep their plants from becoming too vertical.

Pre-flowering phase

Also called the stretch, this takes one day to two weeks. Most plants last for 10–14 days after switching the light cycle to 12/12. Plant development increases dramatically, with the plant doubling or more in size. (See reproductive development below.) Production of more branches and nodes occurs in this stage, as the structure for flowering grows. The plant starts to show calyx where the branches meet the stem (nodes). Pre-flowering indicates the plant is ready to flower. l/rm/su,rh;,7;e,Uy/uvl;n.,8y

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 auto flowering strains that flower independently of photoperiod) can flower under diminished light. In nature, cannabis plants sense the forthcoming Winter as the Earth revolves around 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 attracting insects which may be carrying male pollen. The trichomes produce resins containing the largest amounts of THC and CBD, the two main psychoactive substances. Fertilized females produce resinous trichomes but more plant energy is sunk into seeds, which can be half the mass of a fertilized inflorescence; thus to maximize resin per gram seedless cultivation is preferred.

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). Potent sinsemilla 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.

Indoors, cannabis is 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 in Fall and Winter.^[18]

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 flower with 12 hours of darkness to be safe.

Flowers from certain plants (e.g. 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.^[9][11]

Outdoor cannabis cultivation

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. Outdoor cultivators tend to grow indica-based strains because of its 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 to trees to decrease this possibility.^{[citation needed]}

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.^{[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 is 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 agencies, including the Drug Enforcement Administration, have claimed that in State and National Parks, people have been injured by cannabis farmers protecting their crops using booby traps, although no arrests or convictions have been made.^{[citation needed]}

Detection

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 neighbors, 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^{[citation needed]}. 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 said^[who?] that if the cannabis plant is planted by a pine or cedar tree, the heat from the tree overlaps the cannabis plant heat, making it harder to detect from helicopters, although cedar trees turn the soil acidic.^{[citation needed]}

Indoor Cannabis Cultivation

Indoor Cannabis cultivation.

Cultivating Cannabis indoors traditionally includes growing the plants in a soil-like medium under artificial light and 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. Cannabis grown indoors can be just as potent as its outdoor counterpart if tended to properly. In fact, plants can be grown faster than outside due to 24 hour light, additional atmospheric CO2, and controlled humidity which allows freer CO2 respiration.

Small buildings for cultivation are often known as grow-ops.

Cultivating plants indoors can also be done through the use of hydroponics; however, this method is more complicated and somewhat less common.^[19][20]

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.

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.^[21] For example vegetables grow best in full sunlight, which means 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). Incandescent and mercury vapor lighting are not recommended for use in cannabis cultivation.

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 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 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 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 a single lamp.^[22] 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.^[23]

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 PAR range. One major short coming 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 to. 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, and try to find results from similar grows using that light.

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 cannabis 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 fall upon the plants. 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; However with proper cooling any light type can be moved extremely close to plants to combat the inverse square law and allow best growth. 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 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 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. 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.^[24]

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.

Popularity

Indoor cannabis plant during flowering

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 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 (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. 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 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 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. 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.

Housing damage

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.^[25][26]

Grow-op homes appear to be maintained in their normal fashion on the outside. Nonetheless, there are plenty of telltale 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).^[27]

One of the largest such examples was masterminded by a Markham, Ontario real estate agent, John Trac, who turned 54 rented houses into grow-ops. He has since been convicted and imprisoned, but his second-in-command, Jennifer Wu, is still at large. Hydro companies estimated the value of the electricity stolen and insisted that homeowners pay before hooking them up again.^[28][29]

Contractor and TV personality Mike Holmes has said that while former grow-ops can be had at bargain-basement prices, being sold off by banks or homeowners to recoup their losses, he warns that repairs and remediation can be around $100,000 CAD, which may outweigh initial buyer savings. Holmes noted 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.^[30][31]

Usually, after the police bust a grow-op house, they are supposed to contact the municipality to ensure that the place is cleaned up before it goes to market, while real estate agents and sellers are required by law to disclose that the home was a past grow-op. However, on one episode of CBC's Marketplace, Holmes and Erica Johnson found out that the agents and sellers were frequently dishonest. Furthermore, home inspectors routinely failed to detect tell-tale signs that the house was a former grow-op. During a test caught on hidden camera, the inspectors passed off the former grow-op home as having minor problems.^[30][31]

Harvesting, drying and curing

Close-up of a female cannabis bud in flowering stage. White trichomes can be seen coating the surface, which 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 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 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.^[32]

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.^[33] 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.

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.

Drying

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 to hang the plant from. Roots are removed, and 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 deteriorate if exposed to light and the degradation product CBN forms, significantly altering the cannabinoid profile of the dried flowers.

Curing

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.^[34]

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^[35] though many 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 (THC vaporizes at 157 °C (315 °F ). Smokers usually heat the liquid and inhale the vapors through a straw.

Hash

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 that cannot be smoked – but have, over time, collected many fallen trichomes. Rather than letting them go to waste, they are frozen for 24 hours then agitated in ice water in a 5 gallon bucket lined with a succession of bags having decreasing screen sizes that capture the plant matter and allow the trichomes to pass down to the bottom bag where they collect into a wet paste. The paste is pressed between its screen and a clean absorbent towel to extract water from the paste until it has the texture of clay. The clay (hash) is then shaped and smoked. This type of processing creates hashish called "bubble hash".

"Bubble hash" is so named because of bubbles released (sometimes) as it burns. Pre-freezing the trim for 24 hours reduces bubbling by stiffening and hardening the trichomes. This prevents the trapping of water molecules when the trichomes separate from leaf matter (imagine icicles breaking off a frozen tree branch). The lack of using pre-frozen trim reduces the quantity of trichome separation and it increases the likelihood of "burning bubbles". These bubbles are interesting to see but totally harmless.

Hash oil

Main article: Hash oil

Allowing the ethanol in a tincture to evaporate makes hash oil. However, 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 extracts D9 THC, and leaves water soluble chemicals in the ethanol (certain cannabinoids, proteins, chlorophyll, etc.).

Pests

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

The legal status of cannabis has led growers to implement novel cultivation methods for indoor growing with lamps to avoid aerial surveillance.^[36] 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) "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 harvest.

SOG

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

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.

Light Depreciation: The Inverse Square Law^[37] 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 horizontal 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.^[38] 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.

Hydroponics

Main article: Hydroponics

Example of 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 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 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.

Genetics

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 cannabis, 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 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)

A cultivator decides which plants exhibit the most desirable traits, and takes a cutting that is grown to maturity but never allowed to flower. This plant is a mother, and can be kept for years, producing thousands of clones genetically identical to the mother.^[39]

Feminized seeds

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. It is possible to use a combination of cloning and "shocking" 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 this tendency. Others believe the fact that this method utilizes auto hermaphroditic traits 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.

Colloidal silver 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. Gibberellic acid has also been used for the same purpose, but it is harder to find than colloidal silver. 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.^[40]

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.

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 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.^[41]

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".^[42]

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:

1. 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.
2. The cutting is brought to contact with rooting hormone, according to instructions, to promote root growth and inhibit fungal infection.
3. 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) and direct light is avoided so that the cutting does not dry out. The production from the slower photosynthesis is put into root production.
4. 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.

• 

  "Blueberry" cannabis cuttings waiting to be trimmed and re-cut.

• 

  Trimmed with stem re-cut at 45 degree angle below a node.

• 

  New clones under improvised humidity domes.

See also

• 420 (cannabis culture)
• Cannabis
• Cannabis (drug)
• Cannabis strains
• Grow house
• Hemp
• Hydroponics
• Legality of cannabis
• Marinol
• Medical cannabis
• Organic farming
• Vertical farming

References

1. ^ cannabis
2. ^ Medical cannabis
3. ^ Legality of cannabis
4. ^ Legality of cannabis by country
5. ^ Cannabis – Wikispecies. Species.wikimedia.org. Retrieved on 7 August 2011.
6. ^ Cannabis sativa L. – Encyclopedia of Life. Eol.org. Retrieved on 7 August 2011.
7. ^ 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. http://www.amjbot.org/cgi/content/full/91/6/966. Retrieved 8 October 2006. 
8. ^ Small, Ernest (1975). "American law and the species problem in Cannabis: Science and semantics". Archived from the original on 19 April 2005. http://web.archive.org/web/20050419110112/http://www.unodc.org/unodc/bulletin/bulletin_1975-01-01_3_page002.html. Retrieved 8 October 2006. 
9. ^ ^{a b c} Greg Green (2001). The Cannabis Grow Bible (4th ed.). p. 47. ISBN 1931160171. 
10. ^ Auto-flowering Cannabis Strain: Best light schedule?. Growweedeasy.com. Retrieved on 7 August 2011.
11. ^ ^{a b} Jorge Cervantes. Marijuana Horticulture (5th ed.). ISBN 1878823175. 
12. ^ The Marijuana Grower's Guide (1998) by Mel Frank and Ed Rosenthal, typed by Ben Dawson, revised 1992
13. ^ "Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 153,154
14. ^ Sinsemilla Forums – Cannabis News and Culture. Sinsemillainc.com. Retrieved on 7 August 2011.
15. ^ "Greg Green" The Cannabis Grow Bible, 4th edition (2001), page 164
16. ^ How to grow weed ", Grow Weed, 26 September 2010
17. ^ "Vegetative stage lighting requirements.". www.marijuanagrowguide.net. http://www.marijuanagrowguide.net/Vegetative_Stage.html. 
18. ^ "Marijuana Botany – An Advanced Study: The Propagation and Breeding of Distinctive Cannabis – Robert Connell Clarke". Mellowgold.com. http://www.mellowgold.com/grow/mjbotany-removed/marijuanabotany1.html. Retrieved 16 March 2009. 
19. ^ "Cannabis cultivation using hydroponics". Weedfarmer.com. http://www.weedfarmer.com/growing_guide/hydroponics.php. Retrieved 16 March 2009. 
20. ^ "How to grow hemp using hydroponics". Howtogrowmarijuana.com. http://howtogrowmarijuana.com/hydroponic-marijuana-guide.html. Retrieved 16 March 2009. 
21. ^ "Determining appropriate lighting". Homeharvest.com. http://www.homeharvest.com/whichgrowlightisrightforme.htm. Retrieved 16 March 2009. 
22. ^ toon (1 July 2008). "Cannabis Growing Guide Part 2 – Grow lamps". A1b2c3.com. http://www.a1b2c3.com/drugs/mjgrow4b.htm#A06. Retrieved 16 March 2009. 
23. ^ Lights – High Pressure Sodium AND Metal Halide^{[dead link]}
24. ^ The CO₂ enrichment guide^{[dead link]}
25. ^ "Houses suffer damage from grow-op activities". The StarPhoenix (Saskatoon). http://www.canada.com/saskatoonstarphoenix/news/local/story.html?id=46d17735-c705-436c-abdd-5626ce4d2f59. Retrieved 28 April 2011. 
26. ^ Harvey, Ian (May 2005). "Grow Ops—An Inside Look". Reader's Digest. Archived from the original on 15 April 2005. http://replay.web.archive.org/20050415051452/http://www.readersdigest.ca/mag/2005/05/pot.html. Retrieved 28 April 2011. 
27. ^ Marijuana Home Grow Operations. Nrps.com (2009-01-01). Retrieved on 7 August 2011.
28. ^ Goddard, John (22 December 2009). "Real estate agent jailed, fined M for grow-op scheme". The Star (Toronto). http://www.thestar.com/news/gta/article/741908--real-estate-agent-jailed-fined-1m-for-grow-op-scheme. Retrieved 28 April 2010. 
29. ^ Small, Peter (5 May 2009). "Grow-op king duped 54 homeowners". The Star (Toronto). http://www.thestar.com/News/GTA/article/628985. Retrieved 28 April 2010. 
30. ^ ^{a b} "Grow Op Cover Up". CBC News. http://www.cbc.ca/marketplace/2010/grow_op_cover_up/main.html. 
31. ^ ^{a b} [1]^{[dead link]}
32. ^ Ready – Set – Grow (High Times Marijuana Growing Instructional Video)
33. ^ How to Grow Marijuana: The Basics. Growweedeasy.com. Retrieved on 7 August 2011.
34. ^ Curing Marijuana http://www.sinsemillainc.com/forum/showthread.php?237-Curing
35. ^ hightimes.com grow
36. ^ Expert tips on growing cannabis. Easygrowing.com. Retrieved on 7 August 2011.
37. ^ "Inverse Square Law". http://www.angelfire.com/cantina/fourtwenty/articles/scrogorama.htm. 
38. ^ "The Scrog Method". http://forum.grasscity.com/advanced-growing-techniques/48363-scrog-method.html. 
39. ^ Cloning Marijuana. Marijuana-seeds.net. Retrieved on 7 August 2011.
40. ^ How to Easily Produce Your Own Feminized Cannabis Seeds. Growweedeasy.com. Retrieved on 7 August 2011.
41. ^ Marijuana Genetics. Marijuana Genetics. Retrieved on 7 August 2011.
42. ^ Cloning Marijuana Made Simple. Marijuanapassion.com. Retrieved on 7 August 2011.

Further reading

• 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 1878125028. 
• Starks, Michael (1990). Marijuana Chemistry: Genetics, Processing & Potency. Ronin Publishing. ISBN 0-914171-39-9. 

External links

• Marijuana Farms: A Primer – slideshow by Life magazine
• LED Grow Lights
• LED Grow Lights Blog