Greenhouses are becoming the most popular way to cultivate cannabis. They harness the power of the sun, provide a warm climate, and protect gardens from harsh environmental conditions. Past the basics, a greenhouse allows for year-round cultivation, climate control, and controlled exposure to sunlight. What’s more, they’re cheaper than growing indoors and produce a more consistent product than outdoors.
How Does a Greenhouse Work?
How does a greenhouse stay warm even when the outside air temperature is low? This happens through a process known as the “greenhouse effect.” Solar radiation (energy from the sun) passes through the transparent walls of the greenhouse and heats up the soil and plants. In turn, the soil and plants release this energy as infrared radiation which cannot escape the greenhouse. The heat is trapped and warms the air. On a hot day, you experience the science behind a greenhouse when getting into a parked car that has been left in the sun.
The greenhouse effect opens up the doors to year-round cultivation. However, cannabis is a demanding plant that needs both adequate lighting and controlled exposure to lighting in order to harness its continual offerings.
Recreating the Cannabis Life Cycle
In the fall, winter, and spring, the sun stays lower on the horizon. Because of this, plants receive less energy and have a harder time growing. Cannabis requires sunlight for more than 12 hours a day to stay in vegetative growth. Once the plant receives 12 hours or fewer of sunlight a day, it will start to flower and produce trichome-rich buds. Outdoors, plants generally go in the ground around June, grow in a vegetative state in the long days of summer, and then begin to flower in the early fall when the days become shorter.
Advanced greenhouses allow for the control of the light cycles needed to cultivate cannabis. These greenhouses go far beyond just keeping the plants in a warm climate. Other manipulation tools include supplemental lighting, climate control equipment (dehumidifiers, heaters, air conditioning), and the ability to block out all incoming light.
Advantages of Growing Greenhouse Cannabis
Growing cannabis in greenhouses can be advantageous over regular outdoor growing. These four key reasons outline why many growers are turning to greenhouse cultivation.
Supplemental lighting allows for the gardener to extend the hours of daylight. It also allows the gardener to improve the quality of light on overcast days. Extending daylight hours gives the gardener the ability to keep the plants in a vegetative state and control their natural course. Improving the quality of light with supplemental lighting also helps keep plants healthy and growing vigorously even when the weather is less than ideal.
Weather and Climate Control
Having a controlled climate is essential to produce a top quality product. Protection from the outdoor elements help keep the product safe. For example, heavy rains often result in damaged plants and rot if too much moisture is trapped inside the bud. Plants in a greenhouse are protected from rain and have windows that can be “burped,” or have dehumidifiers to control humidity. In addition, greenhouses may have heaters, air conditioning, and fans, all of which may be used to create a consistent ideal climate to grow while still harnessing the power of the sun.
Manipulating Life Cycles
A common practice among greenhouse farmers is to run cycles of plants known as “light deps,” or light deprivation, during the summer season. It allows the grower to harness the summer light while, at the same time, limit the light exposure the plant receives to trick the plant into flowering prematurely. This greenhouse technique mimics indoor lighting cycles and allows the greenhouse grower to harvest a crop in early August, replant, and then harvest a second crop in the fall.
To continue producing crops during the fall, winter, and early spring, the gardener leans more heavily on supplemental lighting and heaters. On winter solstice in Seattle, for example, we receive less than eight and a half hours of daylight. In addition, that light is very low in the sky and poor for gardening. In a greenhouse, that light would still help heat the greenhouse, but the gardener would need to use supplemental lighting to maintain a quality product and to extend the hours of light in the day.
The ability to balance light exposure, use supplemental lighting, and keep the climate stable allows for year round cultivation just like indoor growing. The difference is that the grower only uses supplemental light mechanics when Mother Nature is not providing an ideal environment. This results in substantial energy savings while the quality of the product stays consistent.
Many crops that require specific environments are already produced in greenhouses, including tomatoes, leafy greens, and peppers, so it’s only natural that cannabis finds itself at home in greenhouses as well. As cannabis legalization spreads, farmers are finding it safe and financially beneficial to move from warehouses to greenhouses as the industry develops.