Greenhouse Cannabis Cultivation Basics for Wintertime Growing 

The financial benefits of utilizing sunlight – as opposed to artificial lighting – in greenhouse cannabis cultivation operations can be staggering. Still, most North American cannabis cultivators opt to move their grow operations indoors during the winter months. As such, they pay exponentially large electrical bills. Nonetheless, for the industrious cultivator, it is possible to reap bountiful, sun-fueled harvests in a greenhouse during the depths of the cold winter.

Driven by ever expanding technological innovations, the complexity and sophistication of greenhouse cannabis cultivation operations are practically boundless. However, it is safe to assume that increased automation is jointly tied to increased expenses and decreased labor. Point being, the less money one is willing to spend on a wintertime greenhouse crop, the more human attention it will require. With these notions in mind, here are a few guidelines covering the basics of wintertime greenhouse cannabis cultivation:

Climates and Greenhouse Frames

The sort of climate being engaged will be the primary factor in helping cannabis cultivators decide how to construct, control, and cultivate a prospective winter greenhouse cultivation operation. Correspondingly, the colder a geographical location is, the less options there will be for growing a successful crop. Along this line of thought, for both cold and temperate climates in North America, hot frame greenhouses are the only option for wintertime cultivation.

Hot frame greenhouses are generally permanent structures which can hold up to the intense demands of wintertime gardening. Because, they provide the platform and infrastructure for effective climate control. Greenhouse frames can be custom built by professional carpenters and builders. However, a majority of horticulturalists prefer the simplicity of greenhouse kits. In conjunction, wintertime gardening requires well insulated, thick greenhouse walls. Depending on one’s budget, these walls can be constructed with fiberglass, glass, Sollex, and polycarbonate.

Heat Sources for Greenhouses

When cannabis cultivators are planning a wintertime greenhouse horticulture operation, it’s crucial to understand that controlling a constant temperature is extremely difficult. Again, the more money one is willing to spend on cultivation technology, the more effectively one can maintain an ideal atmospheric equilibrium. With a well-insulated greenhouse, wintertime cultivators have to balance climactic requirements with both heating methods and supplemental lighting.

In the design of a greenhouse heating system, cannabis gardeners need to weigh both ambient temperature and root-zone temperature against the demands of their desired crop. In geographical locations where temperatures are cold enough to freeze the ground, keeping root zones warm is an essential practice. Root zones can be protected by: growing in raised beds off the ground, using heating mats beneath pots, and running hot water in tubing beneath pots. Finally, ambient temperature in a greenhouse can be controlled with a variety of methods which are dependent upon greenhouse size, outdoor climate, and budget. These begin with a simple electrical space heater for your novice operation. Moving up, cannabis growers utilize thermostat controlled, industrial propane heat sources for large scale operations.

Supplemental Lighting

For cannabis cultivators interested in growing light-intensive crops in the midst of winter, supplemental lighting is a must. Generally speaking, DE HPS lights are utilized in wintertime greenhouse gardens to supplement sunlight on cloudy days. They also extend growth periods on short winter days. Supplemental greenhouse lighting has two serious implications for the wintertime gardener. To begin with, HPS DE lights emit a large amount of heat. As such, this heat must be balanced with the ambient temperature in the greenhouse during both day and night. Secondly, these lights are expensive to operate and should be utilized under consideration of a cost/benefit ratio. For growers in the Northern states, this ratio makes it obvious that it’s less practical to grow light-intensive plants in greenhouses than indoors during the winter.

Interview with California Wintertime Greenhouse Grower Mike Sheet

For cannabis cultivators in warm and temperate climates, however, wintertime greenhouses are economically viable. To further illustrate the challenges and benefits of wintertime growing in a temperate climate, I asked Mike Sheet, a Northern California greenhouse cannabis cultivation expert, for some detailed advice. Here is our short Q and A:

Is expensive automation a necessity in wintertime greenhouse cannabis cultivation?

Mike: “That’s totally dependent upon your goals and lifestyle. If you have an industrial size grow operation, it’s a must. Otherwise, it’s going to be a really hands-on experience 24/7.”

How do you deal with the extreme temperature fluctuations of greenhouse cannabis cultivation?

Mike: “I have an industrial propane greenhouse heating system which is ran by a thermostat. This is used in conjunction with industrial dehumidifiers so that we exhaust the greenhouse as little as possible. In this way, the exhaust system doesn’t pull in cold air from outside and push out the warm air from the heating system.”

How much do your supplemental lights really have to work?

Mike: “We have 20 DE lights in a 30ft x 96ft greenhouse that we use during both the vegetative and flowering cycles. During the veg phase, we provide 18hrs of light during the short winter days. Once we reach flower, we use our lights only on cloudy days. But, when it’s sunny, like it is most days in California, we don’t need to turn the lights on at all because the short days trigger the 12/12 photoperiod. So I’d say, during flower, we use the lights on 1/3 (33%) of days.”

What are your estimates on power savings when compared to traditional indoor cannabis growing?

Mike: “You have to consider the size of your canopy against what you are paying in electric bills. It’s tough to give an exact figure because the amount of time we use our lights (during flower) is totally dependent upon the weather. However, our canopy is 1720 square ft. (86ft x 20ft) with 20,000 watts in electricity. When you compare this figure against an indoor operation canopy at 400 square ft. (20ft x 20ft) and 16,000 watts of electricity the savings per square ft. are already quite evident, even during vegetative growth. When it comes time to flower and we only run the lights 1/3 of the days, the savings are astronomical.”

 

This article originally appeared in the February 2017 edition of Maximum Yield Magazine.