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Misconceptions about growing cannabis in greenhouses

Sept. 29, 2016, Vineland Station, Ont. – As the cannabis industry continues to gain legal status around the world, more and more cannabis growers are learning about commercial scale horticultural production techniques, and of course, that means greenhouse growing.

October 2, 2017  By Leigh Coulter

Anxious to grab a piece of the hottest industry of our generation, many consultants have jumped into the picture claiming to be manufacturers and greenhouse experts. Unfortunately these groups are not always well informed and often perpetuate wrong thinking.

Here are the 10 most frequent misconceptions we hear being told to cannabis growers looking to move to greenhouse growing.

1/ You can’t grow in a greenhouse in the winter.


If someone tells you this, walk away right away and block their email address because they clearly have no understanding of the greenhouse industry. Tomatoes, peppers, roses, lilies, lettuce, etc. are grown in abundance throughout Canada, the northern U.S., Europe and Japan year round.

Niagrow Systems was established in 1978 with the sole purpose of providing top quality heating systems for greenhouse growers throughout North America, and thousands of greenhouse growers can attest that with a properly designed greenhouse heating system, quality plants can been grown year-round.


2/ You must heat a northern greenhouse year-round.


Only slightly less ridiculous than the first statement, this comment is an indication of little understanding of how greenhouse technology is adapted to different geographic needs. Often smaller companies who are more locally focused will make this kind of error. If the company you are working with is not from your geographic region then, take this misstatement as a sign that they are not knowledgeable enough to give you proper greenhouse advice.

Greenhouse heating design experts factor in the climactic region, the style and size of greenhouse, the specific needs of the crop, and the insulation factor of the greenhouse glazing material. Properly designed greenhouses are built to provide the ideal environment for your crop. If you consider how often your climate is below your desired cannabis crop temperature, you will quickly see what percentage of the year you will need to be able to heat the greenhouse.

3/ You must provide year round air-conditioning for southern greenhouses.


A modification of the northern greenhouse misconception, these misinformed people are painting a large region with a single brush. Every project needs to be looked at individually because there is no one and only “cannabis greenhouse.”

For instance, in southern California, Mexico and eastern Texas, fan and pad systems work very well for greenhouse growers. However in environments with higher humidity levels, as in Puerto Rico, fan and pad systems are not effective. A greenhouse without a cooling system of some type will not be able to get below ambient temperature, so considering your climate will help you determine if additional cooling is needed, and if so how often.

4/ Dutch greenhouses manufacturers understand cannabis growing best.


In the Netherlands, growing cannabis is illegal. With all the freedoms that Amsterdam offers cannabis consumers, growing the plant is not legal. On the other hand, medical marijuana has been legal in California since 1996, and legal in Canada since 2001. North American greenhouse manufacturers have considerably more experience with legal cannabis growing than manufacturers from other parts of the world. At GGS Structures Inc. we have been helping cannabis growers increase their yields for decades.

5/ There is a specific greenhouse design for cannabis.


This one is popular with supply companies who are interested in fitting growers into a cookie cutter model rather than working with the grower to find the best solution for them. Greenhouses have many different options, and growers should want to work with a greenhouse manufacturer that is interested in helping them grow. Different geographic regions and different licensing regulations require different growing techniques, systems, and greenhouses.

6/ I don’t need heat in a greenhouse because I have lights.


There is a great deal of talk within the cannabis industry about the amount of heat that lights generate. When you move from an indoor grow to a greenhouse you will still want to have lights, only in a greenhouse the lights are for supplemental purposes to give you a boost when natural daylight is not enough.

So if you want to use your lights for heat, and you are growing cannabis, and you want light for only 12 hours a day while flowering, you still have 12 hours that potentially need heat but have no light. And since this 12-hour period is going to be at night, the temperatures outside the greenhouse will also be lower temperatures.

7/ High-tech greenhouses grow top quality cannabis, and mid-tech greenhouses grow mid quality.


While some greenhouse manufacturers and consultants would like to believe the entire success of a grower is due to the greenhouse structure and greenhouse equipment, this is just not the case. Top quality growers will grow top quality plants, and poor quality growers will grow poor quality plants. What the right greenhouse structure and the right greenhouse systems will do is make it easier for good growers to grow top quality cannabis.

Many of the systems, like environmental control computers, light deprivation screens, rolling benches, fertilizer injectors, etc. are more about production efficiency than specific plant quality. Plant quality generally goes up with proper use of high tech greenhouse systems because the automation reduces human error variables. Often it is wiser to add technology in stages so you and your staff are able to fully understand the benefits of new greenhouse systems.

8/ The capital investment in a greenhouse is more than in a warehouse.


In building a greenhouse the capital investment is typically significantly less than a warehouse indoor grow operation. If you believe that growing cannabis in a greenhouse is the right approach for you, make sure you are building a relationship with a real greenhouse manufacturer, a company that can show you how to get the most value from your greenhouse build.

Greenhouse large-scale agricultural growing techniques and equipment allow cannabis greenhouse growers to gain on both operational efficiencies and capital cost savings.

9/ Light deprivation is brand new technology.


If you hear this one, I refer you back to my comments on #1 …  walk away fast and block their email address, because they clearly have no understanding of the greenhouse industry.

Outside the cannabis industry, light deprivation curtains are referred to as blackout curtains. This is common commercial greenhouse technology used for many plants that benefit from adjusted daylight hours, including poinsettias, kalanchoes and chrysanthemums.

Vertical and horizontal curtains, light traps on fans, and more help cannabis growers use economical commercial greenhouse technology to adjust the environment inside the cannabis greenhouse to the ideal plant environment.

10/ You can expect an ROI of less than a year for a cannabis greenhouse.


Fantastic returns on investments are often quoted by equipment suppliers and consultants to garner excitement and separate you from your money. Don’t believe anyone that is too quick to throw out ROI promises without taking the time to understand your business plan. There are a lot of people thinking cannabis is easy money, but those of us who have been in the business for a while know this is far from the truth.

At GGS we can help you identify options that will reduce energy costs, save on labour, and increase yield, and if you decide to stay with an indoor grow instead of moving to a greenhouse we can help you there as well.

If you are looking for a greenhouse structure I hope you will contact the professionals at GGS who have been supporting commercial scale growers of cannabis as well as horticulture and food production for decades.

Send us your questions about growing cannabis in greenhouses.

Leigh Coulter is president of GGS Structures Inc. and Niagrow Systems Ltd.

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