As cannabis legalization continues to sweep the nation—and the world—those already immersed in traditional greenhouse agriculture may consider converting their facilities to support this new crop. However, growing cannabis or hemp might require more adjustments to existing operations than initially anticipated, and comes with its own unique crop needs, growing conditions and regulations.

Dr. Nadia Sabeh, president and founder of Dr. Greenhouse Inc., an agricultural and mechanical engineering firm that specializes in the design of HVAC systems for indoor plant environments, has dedicated her career to helping farmers control their environments to grow crops indoors, in greenhouses and in locations that would otherwise make it impossible or impractical to do so. Here, she shares advice on how to successfully make the switch from growing traditional crops to cannabis or hemp in a greenhouse environment.

Cannabis Business Times: What are some things that greenhouse growers should take into consideration when deciding whether to expand their operations into cannabis or hemp?

Nadia Sabeh: I think one of the main considerations is, what were you growing before? [Can] the setup and the design of that greenhouse serve cannabis or hemp? If you were growing vining crops before that were tall and required maybe a similar climate management system and lighting requirements, such as tomatoes, and wanted to convert that greenhouse to grow cannabis or hemp, a lot of the environmental requirements are similar to both of those crops. You need a certain temperature and humidity to have high quality and high yield for that crop. So, the conversion from tomatoes to cannabis is pretty simple, and you don’t have to make a bunch of major changes.

Now, if in that greenhouse, you were growing orchids or even lettuce, the setup is going to be very different. You might not have needed supplemental lighting. The plants might have liked it more humid. The growing system might be very different. Lettuce might have been grown in deep water culture and in rafts, and now you want to rip all that up so you can put benches down for cannabis. So, I think one of the biggest considerations is what was grown before, and is it an easy conversion to grow this new plant, cannabis or hemp?

In addition to that, I know a lot of people in California have purchased old ornamental greenhouses that had wood frames and old plastic coverings, and I think what a lot of growers discovered—too late maybe—[is that] a wood structure is a lot more susceptible to rot, mold and rain. If you’re converting that greenhouse from a crop that didn’t need a lot of light, you might want to replace that [plastic cover with a] cover that’s more transparent to the PAR spectrum that the hemp or cannabis plant will enjoy more.

CBT: How else are the needs of cannabis and hemp plants different from traditional greenhouse crops?

NS: It comes down to light. If you had a low-light crop, like lettuce, for instance, that requires somewhere between a third and a fourth of the light that your cannabis plant needs, [then] that greenhouse probably did not have supplemental lighting. So now, do you need to add supplemental lighting to produce consistency year-round? I think, unless you’re anywhere other than the sunbelt of the U.S. or closer to the equator, the answer is going to be yes, you’re going to need supplemental lighting, because those other crops didn’t need that much light.

You’re also trying to control the photoperiod. Maybe you were growing poinsettias in Pennsylvania. Lucky you, you have light dep already installed in that greenhouse that you could use for cannabis and hemp during that flowering period to control the photoperiod down to eight hours. But if you were growing lettuce, you don’t need light dep. You might not even want shade if you are in Pennsylvania because you want as much light to come in and you don’t really care about blocking light out, and the plants are going to be pretty happy with whatever you give them, whenever you give it to them.

CBT: What other changes should greenhouse growers make to their facility’s design and growing conditions to support cannabis and/or hemp crops?

NS: Lighting is a really big piece of that, and if you do end up adding supplemental lighting, [then] your power, your electrical service to the site, might not be sufficient to support your cannabis or hemp project. A lot of these greenhouses might be out in rural areas, so it might be hard to get a service upgrade or get power out there. So, what are your other options? It’s going to be running off of propane tanks, or maybe you’re lucky and have a natural gas line and you can generate power from that to produce the power you would need for supplemental lighting.

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You might have an automated control system already installed, and you can just make some minor changes to that system, changing where your sensors are located or changing what your temperature and humidity targets are. Some of that might be very useful to repurpose for a cannabis or hemp crop, but you might also find that some of that is pretty obsolete and old, and you might want something that’s more sophisticated to control your cannabis production.

CBT: What are some of the biggest lessons you’ve learned, or some of the biggest mistakes you’ve seen cultivators making when converting existing greenhouses to grow cannabis and/or hemp?

NS: [Growers] buy the structure without realizing that [they] have to replace the covering, and the structure that [they] have—this wood frame structure or this aluminum structure—can’t support the weight of an upgraded covering or the light dep system or the shading system or all the lights that [they] want to install. Now, all of a sudden, you’re limited by how much weight the structure can actually support. So [now], you can’t grow anything in this lightweight or wooden structure. Now [you] just have to tear it down, and what [you] really just bought was land.

Up and down the central coast, that has been an issue that some folks and developers have had to tackle, and they’ve tackled it [with] different strategies. Maybe you have to tear it down, [but] it’s like building a house—as long as you keep the demising wall and one wall standing, then you can build everything new around it, and you don’t have to change the building code and you don’t have to upgrade certain things. Maybe some developers can work the system that way and get grandfathered in because they kept the legacy structure there but ended up building a brand new one that fits their needs better. That’s always an option.

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Ultimately, we want to be able to customize the design of the greenhouse, specifically for the plant that you plan to grow. There are some tomato growers who have forayed into cannabis, and very quickly, I think some of them learned that it was a lot harder to control humidity in cannabis plants than it was with tomatoes. Tomatoes are very resilient. They like it hot and humid, or at least they do fine in those conditions, but with cannabis, you really want to keep humidity under control because the part of the plant that you’re selling is the part of the plant that also happens to be susceptible to mold and pesticides and has to go through lab testing, where tomatoes, [if] powdery mildew gets on the leaf, you’re not selling the leaf. You’re selling the fruit, and as long as the fruit is good, you’re good.

CBT: What do you hope attendees will bring back to their business from your session at Cannabis Conference 2020?

NS: I hope that growers come back with at least one or two takeaways that they can apply immediately when they get back to their facility or back to their design team or back to their grower. [I hope] they can say, “Hey, have we thought about this? What are we doing with lighting? What are we doing with the irrigation system? Can we reuse the sensors and control system? Do we need to find new ones because these are out of calibration? Do our exhaust fans actually pull the amount of air that it says right there on the side of the fan box?” I really want attendees to go back asking those questions, and [to] look at the properties and the greenhouses that they’re considering [purchasing] and [renovating], to think about it with a different perspective and make more informed decisions about that investment.

Editor’s Note: This interview has been edited for style, length and clarity.