Greenhouse Canada

The Great Marijuana Greenhouse Debate

November 21, 2016  By Leigh Coulter GGS president

Nov. 21, 2016 – Just before the election I read an article about California pot growers paying millions of dollars for old greenhouses in the Salinas Valley. After the results of the U.S. marijuana elections, greenhouse property values are likely increasing in eastern states like Massachusetts and Maine as much as they are in the West.

To recap the 2016 U.S. election results for marijuana: California, Nevada, Massachusetts and Maine, legalized recreational marijuana increasing the projected annual marijuana crop values by billions of dollars. Additionally Florida has expanded its medical marijuana program and North Dakota and Arkansas joined the rising worldwide trend for establishing legal medical marijuana programs.

All over the country greenhouse growers who are considering cannabis as a viable legal crop as well as existing indoor cannabis growers are paying attention to the potential for growing marijuana in a greenhouse. In the U.S. there are now 29 states in total with legal marijuana, either medical or for adult recreational enjoyment, and growing marijuana in a greenhouse is viable in every single state.



Without a doubt greenhouse construction for marijuana cultivation is on the rise, gone are the days of small basement growers; this is the rise of commercial cannabis production.

With legalization, marijuana growers have newfound opportunities to capitalize on proven agricultural technical innovations, processes, greenhouse structures, and equipment. There is a rush for many growers and investors to get in on the ground floor. Wise capital expenditures for cannabis in the early days can yield a quick return on investment, and this is fueling the need to build greenhouses or large-scale indoor cannabis cultivation facilities as quickly as possible.

When considering buying and improving upon an old greenhouse vs. building new greenhouse there are typically three main motivations: cheaper, quicker to get to production, and easier for someone not well versed in construction. But if money, speed, and lack of construction knowledge are not the issue, it is almost always better to design and build a new greenhouse specific for your individual needs.

Buying an existing greenhouse generally means there is no additional permitting, power sources, land and water use requirements. You may or may not need a building permit for the structural changes and equipment modifications. Eliminating these construction requirements is a big plus for growers considering purchasing an established greenhouse structure.

Having said that, not all existing greenhouses are created equal, and often a buyer will discover too late that the investment in time and money to renovate an existing greenhouse proved to be far greater than it would have been to have built from scratch.

While an existing structure is often enticing when considering speed to planting it is often not in fact the fastest route to a quality cannabis crop. Older greenhouses may not be equipped with the newest technology, or the most efficient layout for cannabis cultivation. But while some greenhouse manufacturers will claim that a marijuana greenhouse is uniquely custom, it is possible to retrofit a quality greenhouse structure with the necessary equipment for growing marijuana.

Here are a few considerations to consider before purchasing an existing greenhouse with the intention of converting it to a marijuana greenhouse.

1. Consider the Age of the Greenhouse

There have been significant advancements in greenhouse cultivation technology and environmental controls over the last 15 years. A greenhouse that was built in the 1990s or before may not have been designed for the building code requirements that exist today or for supporting the automation technology that you will inevitably want to incorporate into your marijuana greenhouse.

2. Don’t Buy Any Greenhouse with an Under-Gutter Height Less Than 14 Feet

Cannabis growers who are growing trees should be looking at under gutter heights of 16 or 18 feet if possible but even for sea of green commercial greenhouse growers know the value of good airflow, and low gutter heights make indoor environmental control more of a challenge.

3. You Will Need to Add Odour Control

In many jurisdictions in Canada and the U.S. marijuana growers have strict regulations regarding marijuana odor control. No existing commercial greenhouse growing a crop other than cannabis will have any systems for preventing the smell of the crop from escaping the greenhouse. We have odour control systems that can be added to existing greenhouse structures just make sure that this is factored into your decision on whether to buy an existing greenhouse or build a new greenhouse. Even in areas where odour control is not currently an issue be aware that it is highly likely this will become something that will have to be added onto your greenhouse in the future.

4. Cannabis Requires Light Deprivation If You Want to Get the Maximum Production from Your Greenhouse

Not all crops benefit from light deprivation and while there are several crops that do, as an investor looking at an existing greenhouse facility you need to thoroughly assess the light deprivation curtains for your cannabis needs. Cannabis is a short-day flowering plant, and as such, light deprivation is required to stimulate the crop to flower while natural days are longer than 12 hours. Don’t forget that if the greenhouse has exhaust fan, ventilation light traps for the fans will also be required. Adding curtain systems to existing greenhouses can be complicated if the greenhouse was not built with the intention of ever adding curtains. Work with a reputable greenhouse manufacturer to determine the best way to facilitate the construction.

5. Grow Lights Are Also Equipment Recommended for Growing Marijuana in a Greenhouse

While cannabis flowering can be forced by blackening out the greenhouse for 12 hours, you do want to make sure that you have adequate light levels for the other 12 hours each day. And in the vegetative stage the marijuana plant requires a greater amount of light to thrive. A proper light layout specifically for marijuana cultivation is essential to increasing yields. Even if an existing greenhouse has lighting there is a good chance that the layout will not be what you need for marijuana cultivation.

6. As with Regulations to Keep the Smell of Marijuana from Escaping the Grow Site, Light Pollution Has Recently Become an Issue for Some Community Regulators

When we design marijuana greenhouse facilities we recommend that the greenhouse structure be designed to have blackout curtains (light deprivation curtains) in all rooms, including veg rooms in order to enable the cannabis grower to prevent light from escaping the greenhouse. Even if this is not a requirement today you want to be able to add blackout curtains should regulations be passed in the future that restrict your ability to turn on your grow lights at night. To maximize the number of turns you get and maximize bud production annually you need to be able to use your greenhouse lighting system year round. So when looking at existing greenhouses consider how you will add blackout curtains for light deprivation and eliminating light pollution in every room: flower and veg.

7. Consider the Total Greenhouse Layout and How You Will Separate Zones into Cultivation Rooms

Odds are your new marijuana crop is going to be 10 times more valuable than the crop that was previously grown in this greenhouse space. Commercial greenhouse structures are designed typically for large production areas that improve production efficiencies for commercial plants. On the other hand commercial marijuana growers are striking a delicate balance between large-scale cultivation facilities, and crop protection isolation rooms. Greenhouse manufacturers commonly provide for separate cultivation areas inside the commercial greenhouse by segmenting zones. The zones may or may not be separated by inside walls however they almost always enable a grower to change the environment of the area through separate controls of ventilation, irrigation, heating, shading and blackout, and lights. To retrofit an existing greenhouse structure for growing cannabis you need to look at the existing zone layout and compare that to your ideal room layout. The closer the existing zones fit to your desired plan the easier it will be to get the existing greenhouse structure into production for marijuana.

8. Consider the Cleanliness and Overall Condition of the Existing Greenhouse

If a greenhouse has not been well maintain the expense of getting it in working order can be considerable. Not all problems will be easily identified before you begin the cleanup. A healthy contingency for time and dollars should be added to the budget. In addition to cleanup issues with equipment that may not be functioning at optimal levels, over time pest populations can establish into the structure itself. A messy greenhouse over-run with weeds will certainly have resident pests to contend with. It’s good to understand what crops were grown in the structure and nearby areas, in order to take steps to understand what pests may be problematic moving forward. You may need to perform aggressive pest control as part of the retrofitting process.

9. Build a Comparative Budget Between a New Greenhouse Construction Project and a Greenhouse Renovation Project

At GGS we can provide you with a handy tool to help you compare what is required in the event of improving on existing greenhouse versus building a new greenhouse.

Remember any construction done around existing systems and equipment takes longer than a new site because construction workers and equipment have to move around what is in the way.

Whether you are retrofitting existing greenhouses for marijuana or building your marijuana greenhouse from scratch, remember the purpose of the greenhouse is to provide the best environment for your crop. To grow quality cannabis as efficiently as possible marijuana greenhouse growers are investing in advanced technology. Whether you are retrofitting an old greenhouse with today’s technology or building a new greenhouse GGS is happy to help you build the best environment for your crop.

Leigh Coulter is the president of GGS Structures Inc. and Niagrow Systems Ltd. GGS has been building greenhouses for growers around the world since 1979. Learn more at

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