A cannabis plant’s flowering cycle is triggered by its photo-period. In other words, the length of time a cannabis plant receives light in a 24 hour period directly influences the plant’s hormone production and can trigger the creation of flowers or buds. Marijuana’s photo-sensitivity is why indoor cannabis growers use a 12 hour “lights on” and a 12 hour “lights off” photo-period during the flowering stage of growth. It is actually the lengthening of the dark period that prompts a cannabis plant to enter the reproduction stage (flowering stage). Marijuana’s natural response to the photo-period is the basis of a gardening technique which is becoming increasingly popular among greenhouse cannabis cultivators. This gardening technique is termed light deprivation.
The practice of shading a greenhouse to control the photo-period is called light deprivation. Put another way, light deprivation gives a horticulturist the ability to shorten the length of sunlight hours per day; triggering the cannabis plant’s flowering cycle. Light deprivation greenhouses give the grower heightened control over the photo-period and allow him or her to flower marijuana plants earlier than they naturally would. Most light deprivation greenhouses have a transparent material (glazing) that is identical to any other greenhouse.
Unlike typical shade cloths that only reduce the amount of light entering the greenhouse, the outer covering material used for light deprivation is designed to shade as much light as possible. In order to make the interior of the greenhouse as dark as possible, the shading material used for light deprivation needs to cover the entire greenhouse structure. Each day the shade cover is removed for the desired amount of light hours. After reaching the desired length of light hours, the shade cover is manually or automatically put back on the greenhouse.
The biggest difference between light deprivation greenhouses and the way they operate is whether the shade material is manually or automatically removed or moved into position. With a manual light deprivation greenhouse, the shade cloth must be manually positioned over the greenhouse structure. As can be imagined, this can be quite difficult with large structures. Growers usually rely on some sort of rope and pulley system to aid in moving the potentially heavy shade material. Aside from the physical labor involved, the biggest disadvantage of a manual system is that someone (usually the grower) must be present every day for both the covering and removal of the shade material. Forgetting just once can cause problems for a grower, including out-of-whack atmospheric conditions or stunted growth due to quickly alternating photoperiods.
An automatic light deprivation greenhouse is one equipped with a motorized system for covering and removing the light deprivation material. These systems are typically equipped with a small electric motor. These motors can be wired for use with a chain of car batteries to operate in locations without access to electricity. Automatic light deprivation systems offer huge savings in labor and also allow a marijuana grower to use a timer for the system’s motor. With the timer, a grower can automate the system and does not have to be present every time the covering is removed or put back on the greenhouse.
There are some major advantages of using light deprivation for cultivating marijuana, including more control over the harvest time, multiple harvests per growing season, higher quality, increased yields, and a reduced chance of failure.
As with many things in life, timing is everything. A light deprivation greenhouse allows a grower to control the time of flower initiation and, in turn, the time of harvest. This could be advantageous for many reasons, but one reason in particular is the ability to harvest cannabis at a time of year when other growers still have their plants in the ground. Like other commodities, there are times of the year when marijuana is more or less available, which affects its price. The ability to harvest marijuana during a time of the year when the supply of marijuana is low means a higher price for the product and a higher return on investment for the grower.
Another huge advantage of light deprivation in a greenhouse is being able to harvest multiple times per year. Before light deprivation techniques, only indoor gardeners had the ability to harvest multiple times per year. Outdoor cannabis growers were always at the mercy of Mother Nature and could only harvest once per growing season. Light deprivation allows most growers to harvest at least twice during a typical growing season. Marijuana growers who use light deprivation methods will typically have a first harvest in late July and a second harvest at the geographical location’s normal harvest time (usually in October or November). For growers in warmer climates, three or even four harvests per year are possible when using light deprivation techniques.
Many growers using light deprivation believe that the (relatively) smaller outdoor plants produced in their light deprivation greenhouses tend to produce higher quality buds than the typical monster outdoor plants. This is because the smaller plants are much less likely to suffer from bud rot, powdery mildew, or other types of molds that find the moisture pockets of large flowers conducive to growth. Many light deprivation growers also believe splitting up the growing season into two harvests of smaller plants increases the overall quality on average.
The lower likelihood of molds also makes the marijuana more marketable; especially when considering the fact that quality control testing of marijuana is becoming the norm for most dispensaries.
Although each individual harvest is smaller than a typical outdoor harvest, the overall yield for the season will end up being the same or even larger. An increase in overall yield can be attributed to the fact that the first set of plants is flowering under the July sun. This means stronger, more direct sunlight with a higher level of UV light. In addition to the intense July sun, a light deprivation greenhouse lets a grower flower one crop while another crop is in vegetative growth. As soon as the first harvest is complete, the vegetative plants can be put into the light deprivation greenhouse to begin flowering.
By breaking up the outdoor season into two harvests, a cannabis grower can reduce the chance of utter failure. Since he or she will have two harvests, the grower will not experience a complete loss if there is a catastrophe, such as a heat wave or a pest insect infestation. In other words, if one crop is ruined, a grower will still have another crop to help negate his or her losses.
Environmental Control for Greenhouses with Light Deprivation
Aside from the shade material to cover the greenhouse, the equipment needed to grow marijuana using a light deprivation method is much the same as growing in a regular greenhouse. However, there are some environmental control and ventilation factors to consider when operating a light deprivation greenhouse. In a light deprivation greenhouse, the plants will be enclosed during the hottest periods of the summer. This can cause some ventilation issues because opening up the greenhouse also allows light in; therefore, this is not a viable cooling option for a light deprivation greenhouse. Instead, a grower must cool his or her greenhouse by using evaporative coolers, air conditioners and/or mechanical fans. In the late stages of flowering, high humidity can also become an issue. The potential problems from high humidity can be aggravated by the mid-summer heat. Fans, air conditioners, or dehumidifiers may have to be used to help control the humidity in a light deprivation greenhouse. All in all, cannabis growers who wish to use a light deprivation greenhouse must prepare for the temperature and humidity that arises in an enclosed environment during the hottest time of the year.
Light deprivation is a technique that will continue to revolutionize outdoor cannabis cultivation. Marijuana growers with the desire to set up an outdoor growing facility should seriously consider a light deprivation greenhouse. Even a grower with an existing greenhouse may want to consider retrofitting his or her operation
to include light deprivation techniques. Currently, there are many light deprivation greenhouse kits and retrofit options available, but as the popularity of light deprivation continues to grow there will be even more light deprivation specific products available to marijuana growers. The biggest draw to light deprivation is the ability to harvest more than once per growing season. However, the other benefits of light deprivation, including a more consistent, higher quality product, higher overall yields and the reduced likelihood of failure, should be enough to pique the interest of any outdoor marijuana grower. Regardless of the specific reason, there is, and will continue to be, an increasing amount of outdoor marijuana growers reaping the benefits offered by light deprivation greenhouses.
Eric Hopper is a Professional Marijuana Grower Senior Editor.
Images for this article were provided by Greenhouse Megastore.