Indoor Cannabis cultivation

This article is about methods of cultivating plants indoors, growing the them in a soil-like medium and adding fertilizer when the plants are given water. Cultivating plants indoors can also be done trough the use of hydroponics; however, this method is somewhat less common Cultivating plants indoors is more complicated and expensive than growing outdoors, but it allows the cultivator complete control over the growing environment. Plants grown outdoors (eg cannabis) can be just as potent as its indoor counterpart if tended to properly.

Basics

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.

Applying light

To determine the appropriate lighting (and the best lamp to use), the specific needs of the plant must be considered. To arrange optimal lighting, the lighting present in the plant's natural environment needs to be imitated. For example vegetables grow best in full sunlight, which means in practice that as much light as possible must be supplied to grow vegetables indoors (fluorescent lamps, or MH-lamps are thus preferred). Foliage plants (eg Philodendron) grow in full shade and can therefore grow normally with relatively little artificial light (thus for the latter, regular incandescents may already suffice).

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 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. Unlike high pressure sodium lamps, metal halide lamps also produce ultraviolet radiation, 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 for the second (or reproductive) phase of the growth, or they are used by those people who only wish to purchase 1 single lamp. 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.

Recent advancements in LEDs have allowed for the production of relatively cheap, bright and long lasting grow lights that emit only the colors of light required for plant growth. These lights are attractive to indoor-growers since they do not consume as much power, do not require ballasts, and produce a fraction of the heat of HID lamps. The lamps consist of arrays of many wide-spectrum red and a few narrow-spectrum blue LEDs of specific wavelengths. Although LED grow lights have shown promise through plant research by NASA and many universities, it is unknown whether the results are applicable to Cannabis cultivation, as their luminous efficiency is much lower.

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 (with incandescent lamps) to 10 cm (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.

The most 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 is also sometimes used, along with Astrofoil (which also reflects heat), and Foylon (a foil-laminated, reinforced fabric).

Arranging the right atmosphere

When growing indoors, the cultivator should maintain as close to an ideal atmosphere inside the grow-room as possible. The air temperature must be maintained within an ideal range, typically with deviations no larger than 10 deg 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 one or more oscillating fans and possibly an extraction fan.

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.

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.

Phases of growth

Germination

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. 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.

When germinating, the seeds must be kept in a dark, moist and warm environment. Germination occurs once water has soaked into the seed and initiates metabolic processes. The seed soon splits and the embryonic root emerges and begins growing downwards due to gravity. Once anchored the root will push the entire seed out above the soil where the seed shell will be lost to expose two circular embryonic leaves (or cotyledons).

This marks the beginning of the seedling stage.

Seedling phase

The seedling stage of growth begins when the seed breaks the soil and exposes its round “seed leafs” or cotyledon. 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 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 soil moist is important at this stage. During the seedling stage fertilizers are not necessary and should not be given to the plant. The plant often sexes during this stage but will not preflower.

Vegetative phase

When the plant possesses 4 sets of true leafs and the 5th is barely visible in the center of the growth tip, 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.

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.

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 more dense 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:

Topping

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

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.

LSTing

LST stands for Low Stress Training. 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. LSTing is often 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.

Reproductive/Flowering phase

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.

While the flowering hormone in the 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 generally 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; this is called autoflowering, and it is because these strains originate near the equator which does not have the threshold darkness levels in fall.

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.

Increasing popularity

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[1] 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 many growers are reticent about their cultivation.

Further reading

• Cervantes, Jorge. Indoor Marijuana Horticulture. Van Patten Publishing, 2001. ISBN 1-878823-29-9
• 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 Publishing Company,2000. ISBN 1-878125-02-8
• Starks, Michael. Marijuana Chemistry: Genetics, Processing & Potency. Ronin Publishing, 1990. ISBN 0914171399

See also

• Vertical farming
• Grow house

External links

• Marijuana Pictures - Pictures of marijuana growing indoors and outdoors.
• Seedbank Update - The authority for seedbank market research.