Cannabis cultivation: Encyclopedia II - Cannabis cultivation - Traditional indoor cultivation

Cannabis cultivation - Traditional indoor cultivation

This section covers the traditional method of cultivating medicinal or recreational marijuana indoors, wherein the plants are grown in a soil-like medium and fertilizer is added when the plants are given water. Traditional outdoor cultivation techniques are covered in the next section, and alternative techniques, such as hydroponics and organic cultivation techniques, are discussed in the last section.

Cultivating marijuana indoors is more complicated and expensive than growing outdoors, but it allows the cultivator complete control over the growing environment, and will generally produce higher quality marijuana than plants grown outdoors.

Cannabis cultivation - Lighting

The single most important (and expensive) factor for the indoor cultivator to consider is lighting. A greenhouse would be ideal, but even these require supplemental lighting. Since cultivation of Cannabis is harshly punished in most areas, many cultivators must set up a hidden indoor grow room and provide artificial light. Additionally, outdoor cultivators usually start their clones or seedlings indoors, under artificial light.

Fluorescent ballasts and bulbs are very inexpensive and much cooler and more efficient than incandescent bulbs. In marijuana cultivation, fluorescent lighting is useful for growing seedlings and rooting clones, because the light produced is very gentle (unlike HIDs, explained next), and won't burn young and/or sensitive plants. Fluorescents are available in 'warm' and 'cool' spectrums, with 'warm' providing more light in the red spectrum and 'cool' providing more light in the blue spectrum. Cultivators generally use 'cool' bulbs in order to encourage short internodes.

The best type of light to use for indoor marijuana cultivation is a High-intensity discharge lamp (HID). High intensity discharge lamps typically work by passing an electrical current through vaporized gas at high pressure, although low pressure sodium bulbs have gas at low pressure. There are many types of high intensity discharge bulbs, including mercury-vapor lamps, sodium vapor lamps, metal halide lamps, and conversion bulbs for metal halide and high pressure sodium.

The only high intensity discharge bulbs suitable for cultivating Cannabis are metal halide (MH) and high pressure sodium (HPS). There are bulbs available in many different wattages from 75 to 1500 watts, but marijuana growers usually only use between 250 and 1000 watt bulbs.

All high intensity discharge bulbs require a special ballast to run, which is contained in a metal box, which grows warm and hums quietly when in use. A metal halide ballast contains a capacitor and a transformer, and a high pressure sodium ballast contains a capacitor, a transformer, and an ignitor. Recently, electronic ballasts have also become available.

Most metal halide and high pressure sodium ballasts are not attached directly to the bulb socket, but rather are connected by a long cord. These are called remote ballasts, and allow the ballast to be placed in a different room from the bulb to reduce heat and clutter in the grow room. If a light has a ballast attached to the bulb socket, it is usually attached to the reflector as well, and it is called an enclosed ballast. Enclosed ballast systems are usually only available for smaller bulbs, generally about 250 watts or less.

While Cannabis will grow under most light spectrums, a full spectrum is best if possible. This is easy for the outdoor grower, as the sun produces a perfect spectrum of light. Unfortunately, neither high pressure sodium nor MH bulbs produce a full spectrum of light. It is best if both bulbs are used simultaneously, and some devoted hobby growers do, but this is rare in practice, and many people grow high-quality marijuana with just metal halide or high pressure sodium. Both bulbs have advantages and disadvantages, and produce different color spectrums.

Metal halide bulbs produce light that is strongest in the blue spectrum, technically about 4000 Kelvin, or around 460 nanometers. Metal halide bulbs also come in various coated varieties intended to increase the red spectrum, but these are all inferior to a high pressure sodium in the red spectrum.

Metal halide bulbs produce about 65-115 lumens per watt and last up to 12,000 hours. They are available in vertical (BU or BD), horizontal (HOR), and universal (U), which may be burned either vertically or horizontally.

Metal halide is an excellent bulb for vegetative phase of growth, as it encourages short internodes (distance between sets of leaves), and inhibits cell elongation, creating a shorter, stockier plant. Growers with a single ballast often purchase a high pressure sodium ballast, and use a metal halide conversion bulb (a metal halide bulb designed for an high pressure sodium ballast) during vegetative phase.

Unlike high pressure sodium bulbs, metal halide bulbs also produce ultraviolet radiation, which may play a role in increasing the amount of THC produced by the plant.

High pressure sodium bulbs produce light strongest in the red spectrum, technically about 2,200 Kelvin, or around 660 nanometers.

High pressure sodium bulbs produce less heat and more light than metal halide bulbs, producing 97-150 lumens per watt, and they last longer as well, up to 24,000 hours.

High pressure sodium bulbs are excellent bulbs for the flowering phase, and the choice of most growers who have only one bulb. High pressure sodium bulbs are an excellent choice for the reproductive phase of growth, as they trigger a greater flowering response in the plant, and simulate a more autumn-like light spectrum. A high pressure sodium conversion bulb, a high pressure sodium bulb designed to be burned in a metal halide ballast, can be used during the reproductive phase if a grower has a metal halide ballast.

If high pressure sodium is used for vegetative phase, plants will usually grow slightly more quickly, but will also have longer internodes, and may be taller.

Recent advancments 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 produces a fraction of the heat of HID lamps.

The lamps consists of arrays of many wide-spectrum red and a few narrow-spectrum blue LEDs of at 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.

According to the inverse square law, the intensity of light radiating from a point source (in this case an HID bulb) is inversely proportional to the square of the distance from the source. So if an object 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 the most important aspect of maximizing light efficiency. They come in two main types, designed to hold a bulb either horizontally or vertically. Most horizontal reflectors can be fitted with glass and air-cooled to reduce grow-room temperatures, and allow the bulb to be placed closer to the plants, although the glass panel slightly reduces light output. Water cooled reflectors are also available, but are rarely used, as they are very expensive and significantly reduce light output.

• Vertical

Vertical reflectors are generally less practical than horizontal reflectors, as they are less efficient, although they are usually also less expensive. When a bulb is burned in a vertical position, most of the light is emitted sideways, and must be reflected downward towards the plant, which increases the distance that the light must travel.

Vertical reflectors are available in cone and parabolic dome shapes. Cone shaped reflectors are very inexpensive but also very inefficient, and are generally not used. If a vertical reflector is used, it is generally of the parabolic dome variety.

• Horizontal

Horizontal reflectors are much more efficient than vertical reflectors, and generally more expensive. Most growers use horizontal reflectors, as the cost of a more expensive reflector is offset by the savings of burning fewer lights to generate the same light intensity at plant level.

Horizontal reflectors are available in a variety of shapes, most of which are roughly trapezoid shaped, although "bat-wing" or "gull-wing" designs are also relatively common.

Even with the most efficient reflectors and room layout, a lot of light is reflected on the walls of the grow room. In order to reflect this light back to the plants, marijuana cultivators cover the walls of their grow-room with some type of reflective material.

The most commonly used covering is 6 mil 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 inexpensive and very reflective, and some growers swear by it, while others find that it distributes light too unevenly, or is too fragile. A more expensive but very effective option is a fabric called Foylon, which is about as reflective as Mylar, but is much more durable, has more even light distribution, and is easier to install and clean. If cold temperatures in the grow-room are a problem, a good choice is Astrofoil, which is about as reflective as Mylar, and is insulated to reflect heat as well as light.

When growing with artificial light, the light intensity will be very uneven in the grow-room. The plants closest to the light source will receive far more energy (in the form of photosynthetically-active radiation) than plants far away from the source. Additionally, plants will grow towards the light source (this is known as phototropism). In order to address this, many growers simply move their plants around within the grow room in order to ensure that all plants are growing evenly. This is easily facilitated by placing planters on casters.

Another option for the cultivator is to purchase a light mover. A light mover simply moves the light around within the grow-room, so that the plants will grow evenly without being moved, and also allows the bulbs to be placed closer to the plants. Light movers are available in two styles, linear and circular. Linear models have a motor which moves slowly along a rail in a straight line, suspended from which is a light. Circular models have a central motor which rotates two or three arms, from each of which is suspended a light. Circular movers generally allow the light to cover slightly more area.

Cannabis cultivation - Atmosphere

When growing indoors, the cultivator must maintain an ideal atmosphere inside the grow-room. The air temperature must be maintained within an ideal range, with a cooler night and warmer day, and 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 in the room, depending on its size. The elimination of the distinctive odor of flowering marijuana is of great concern to most cultivators as well, and they may employ several different methods to eliminate odor.

A common obstacle for the marijuana cultivator is reducing the high temperature in their grow-room, caused by the HID lights. An easy way to overcome this is to remove the hot air and replace it with cool air. In addition to growing warm, the air in the grow-room is rapidly depleted of CO2, which plants need in order to carry out photosynthesis. The easiest way to maintain adequate CO2 levels in the grow room is to remove the depleted air and replace it with fresh air.

Most cultivators solve heat build-up and CO2 depletion simultaneously simply by using a powerful fan to extract hot, depleted air. Some growers also have a less powerful fan to force air into the grow-room, so that the extraction fan will run more efficiently.

There are three main types of fans employed by marijuana cultivators: axial fans, inline duct fans, exhaust blowers, and centrifugal fans. Axial fans are only used in small closet-type grows, as they can't move air through ducting.

Exhaust blowers are the most commonly used, and are very noisy, although also very powerful, and can operate at high static pressure, which is important to move air through long ducting and/or through carbon filters. Sometimes exhaust blowers are referred to as 'squirrel cage fans', because they have a wheel inside that resembles an exercise wheel for a pet rodent.

Centrifugal fans are also very powerful, and operate at high static pressure, but are significantly quieter than exhaust blowers, and are also significantly more expensive. If ventilation noise is a concern, most cultivators will purchase a centrifugal blower.

Inline duct fans are a type of axial fan that is installed in a length of ducting. These are designed to be installed in long sections of ducting to help keep air moving from clothes dryers and the like, but are not very effective for ventilation purposes, and large numbers are required to move even a moderate amount of air. Additionally, they can handle only very low static pressure.

One of the most common ways for an otherwise careful cultivator to be discovered by neighbors is by the distinctive smell emitted, especially during the reproductive phase of growth, by most strains of marijuana.

One of the most effective, and certainly the most common, way of eliminating odor is by forcing 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. Cultivators must be sure that the air is thoroughly mixed before it is expelled outside, lest some odor escape.

Assuming that adequate light levels are present in the grow room, the limiting factor in plant growth is the level of carbon dioxide (CO₂) levels. Plants grown with supplemental carbon dioxide will grow more quickly, have larger stomata, and can utilize more light. There are two chief tools for increasing carbon dioxide levels in the grow-room: bottled carbon dioxide, and carbon dioxide generators.

The most common way to enhance carbon dioxide levels is by purchasing tanks of compressed carbon dioxide, and releasing it into the atmosphere of the grow room. To do this, the cultivator must purchase a regulator, an emitter, and a tank of compressed carbon dioxide gas. When this tank is empty it can be refilled inexpensively at a beverage supply or welding shop.

Another way to enhance carbon dioxide levels is with a carbon dioxide generator. A carbon dioxide generator is the most cost effective in the long run, but they are initially expensive. They also generate additional heat and moisture in the grow-room. Carbon dioxide generators work by burning either propane or natural gas, and typically have four to eight burners. Propane powered generators use the same type of tank as a gas grill, and natural gas burners can be attached directly to natural gas lines.

The least expensive and perhaps simplest given the required items is the milk jug and yeast solution. Put about five or six cups of sugar in a clean one-gallon plastic jug. To this add about a half gallon of water. Mix until the sugar is dissolved and add a little bit of active yeast. Poke a small hole in the lid and replace it on top of the jug.

Once a day, or as often as possible, shake the jug to thoroughly mix the contents. In a day or two the yeast will begin to grow and CO2 gas will be a by-product in the jug. Once the yeast begins to grow, the shaking of the contents will produce a gaseous eruption through the hole in the lid. On its own, the device will slowly produce CO2 as long as there is enough sugar in the mix and the yeast stays active. The daily shaking stimulates the mix to produce a surge of CO2 gas. Therefore, the more times the jug is shaken, the more surges of CO2 that will erupt into the room. The mix will need to be changed or refreshed every two to three weeks. This system should be more than adequate and perfectly safe for smaller grow spaces (twenty square feet or less). It is also very inexpensive to configure and maintain. This method is actually a very crude method of alcohol production as well, so other economies of colocation may be accomplished with regard to homebrewing.

Cannabis cultivation - Germination

Seeds may be germinated in a paper towel by saturating several sheets of paper towel with water, then placing the seeds inside. The best source of water should be used such as filtered, distilled or spring water. Chlorinated municipal water should be avoided. 5-10ml of water per sheet of paper towel is sufficient. Typically, the paper towel (with seeds) is placed in between two plates, or in a bowl covered with plastic wrap, or in a ziplock freezer bag, to keep the paper towel from drying out. The germinating seeds are then put in a warm (not hot) area, such as on top of a radiator, water heater closet, or above warm lamps. The optimal temperature is between 75-85ºF. Indicas will germinate with lower temps while sativas will need higher temps. Pure tropical sativas will need germination temps of 85-95ºF. Temps over 95ºF will cause thermal death of most seeds. If the container is not light-proof, and it is in an area exposed to light, it should be covered with black paper or something opaque to keep out light. The seeds should be checked about twice a day, misting with water if the paper towel is too dry. Old seeds and less vitalseeds should be rinsed once daily and placed in a fresh moist paper towel to prevent the spread of germination inhibiting bacteria. When a small white root emerges from the seed, tweezers may be used to plant the seeds in a growing medium. This method is not tricky, but if the paper towel is allowed to dry too much, the seeds may never germinate. Seeds should be placed in a neutral soil (minimal fertilizers) with the root tip pointing down. When transplanting the freshly sprouted seed a light sprinkling of soil (just enough to cover the seed) is sufficient, with a few more drips of water to moisten the seed.

Cannabis cultivation - Vegetative phase of growth

When true leaves have formed, the plant begins 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.

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 fertilizer is generally mixed with water, and then applied to the plants, usually every other or every third watering. The cultivator must avoid over-fertilizing the plants, especially when they are young, or the plants will suffer from nutrient burn. As the plants grow larger and stronger, they are able to tolerate a stronger nutrient solution, and the strength of the fertilizer is gradually increased.

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 eminating 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.

Cannabis cultivation - Reproductive/flowering phase of growth

The plant will be induced to flowering by decreasing light from 18-24 hours a day to dark cycles of 11-13 hours that simulate the oncoming winter in the fall as the days grow shorter. As a consequence, it works out well indoors to have two separate areas; one that is used for the initial vegetative state and one that is used for flowering and fruiting. It is mandatory to keep the dark cycle for flowering very dark with no light interruptions, as any light can stall flowering by days or weeks. Flowering generally lasts from 3 to 5 weeks indoors, if growing outdoors it may take somewhat longer, depending on the natural onset of the colder seasons.

Once a plant is big enough to mature, dark periods are required for most plants to flower and bear fruit. This will require putting the lamp on a timer, to create regular and strict dark periods of uninterrupted light. If growing in a greenhouse, the same effect can be created in the Summer (long days) by covering it with a blanket to make longer night periods. For example, a strict schedule of covering the plants at 8pm and uncovering them at 8am for 2 weeks will start your plants to flowering. After the first 2 weeks, the schedule can be relaxed a little, but it will still be necessary to continue this routine for the plants to completely flower without reverting back to vegetative growth.

Outdoors, in spring and autumn, the nights are sufficiently long to induce flowering at all times. If possible, merely bringing the plants from indoors to the outside at these times will permit natural flowering.

A few weeks after reducing the light, many white pistils will begin emerging at every grow tip on the plant. These are the flowers; once you feel satisfied with the number of sprouted flowers, decrease the lighting schedule again to roughly 8-10 hours, simulating late autumn, the time when the cannabis plant reaches maturity and is completely ready for harvest.

• Nutrition

Flowering plants should be given high phosphorus plant food and with little or no light in the dark cycle. 13 hours light, 11 dark for instance may increase flower size while still allowing the plant to go into the flowering mode. Use longer dark periods to speed maturity toward the end of the flowering cycle if time is of the essence. Doing this will however reduce total yield.

• Perpetual harvest

Two shelves can be used, one identical to the other, if strictly indoor gardening is desired. One shelf's lights are set for 12-13 hours, and one is lit continuously. Plants are started in continuous light, and are moved to the other shelf to flower to maturity after several weeks. This flowering shelf should be bigger than the "starting" or "vegetative" shelf, so that it can accommodate larger plants. Or, some plants can be taken outside if there is not enough space on the flowering shelf for all of them near harvesting.

Adapted from the Wikipedia article "Traditional indoor cultivation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki