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How to Control the Cannabis Greenhouse Environment: A Q&A With Dr Nadia Sabeh

By Alexander Beadle

Published: Jan 21, 2021    Last Updated: May 17, 2023
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Controlled environment agriculture (CEA) is a technology-focused approach to cultivation, centralized around the idea of improving crop quality and yield by maintaining optimal growing conditions for a plant across its lifetime. And in the cannabis sector, CEA is taking off.

To find out more about this technology and its use in cannabis cultivation, Analytical Cannabis spoke with Nadia Sabeh​​, PhD, the owner and founder of Dr Greenhouse, Inc., an agricultural and mechanical engineering firm that specializes in the design of heating, ventilation, and air conditioning (HVAC) systems for indoor plant environments.

Cannabis and HVAC systems, heating, and ventilation

Alexander Beadle (AB): How did you become so involved in the agriculture, technology, and engineering sector?

Nadia Sabeh (NS): Working on a farm in rural America for three months, I gained a huge appreciation for farmers, and agriculture in general. The experience instilled in me a certain work ethic and I gained such a huge respect for farmers, for agriculture, and for the sense of collaboration they have to help each other. After coming back from the farm, I was really focused on completing my engineering degree at UC Davis, and then headed to Penn State to study air distribution in commercial mushroom farms. Then I went to the University of Arizona to study greenhouses and look at evaporative cooling and ventilation and water use efficiency for tomato production in a greenhouse in a semi-arid climate.

I realized that in agriculture and in controlled environment agriculture, lots of the same ideas get recirculated. It's always these big exhaust fans, maybe it's some passive ventilation. And I was like, there's this whole industry of mechanical engineering and HVAC engineering for designing buildings. So, I wanted to go learn how to be a mechanical engineer with the idea that maybe someday I could bring back those concepts and that equipment to agriculture as something innovative.

As indoor agriculture and cannabis was really getting hot and was getting legalized in different states, I saw that I could realize my dream. This was my opportunity to combine the two things I love in controlled environment agriculture and HVAC engineering into a company focused on HVAC design for indoor farms and greenhouses. And so I started Dr Greenhouse in January of 2017, and as of today, we have worked on 95 projects around the world to help indoor farmers grow a variety of crops.

AB: For cannabis cultivators, what are the main benefits of setting up in a greenhouse with controlled environment agriculture technology?

NS: For every grower or developer or owner of a cannabis cultivation facility, the first decision they have to make is on the facility. Are we growing indoors? Are we going to grow in a greenhouse? Maybe some hybrid of the two?

The main advantages of growing in the greenhouse, number one, is that your plants are exposed to natural sunlight. Although we know that most plants use photosynthetically active radiation (PAR) for photosynthesis – the spectrum of light between 400 to 700 nanometers – there are studies that show that the edges of that spectrum have benefits to plant production, and we know that some of the middle areas of that spectrum have some advantages to the quality of the plant produced. So, having exposure to that full spectrum of sunlight has some potential benefits, both in terms of yield and quality of the cannabis plant.

The other potential advantage is that if you are in a climate that is conducive to using low energy consumption technology like unit heaters, ventilation fans, or evaporative cooling, that can save the grower a lot of costs associated with energy. Most producers will tell you that the two largest expenses to their operation are labor and energy, and so if you can grow in a greenhouse you can cut that energy use and those costs by 90 percent in some cases. And if you're in an area that can use passive ventilation because it's cooler but still sunny outside – say, like northern Europe – you can open up the vents in the greenhouse and just let that heat escape to the cold outside. A lot of people forget that greenhouses were developed in places like the UK and the Netherlands, in these climates that are colder yet potentially sunny. That's what the greenhouse effect is; it captures the sun’s energy and heats up the greenhouse without using a lot of external heating energy.

Water use can also be an advantage, especially compared to field agriculture. Those people who are trying to grow cannabis outdoors have to use a lot more water usually to irrigate their plants. But, in a greenhouse, you can use a lot less water if you are paying attention to the water content of the media and only giving the plant the water and nutrients that it needs when it needs it. And then if you capture that water that drains off the plants and recirculate it through a filtration or water treatment system, you can really reduce the water use compared to growing out in the field.

Also, greenhouses provide simple shelter from the outside. Shelter from pests and animals that might trounce through your farm. Protection from the elements outside also allows for year-round production when you have a climate management system in place.

AB: So, to get more into the tech side of things, what are the most crucial pieces of engineering equipment to have in place when running a greenhouse?

NS: When it comes to technology – whether we're talking about your irrigation equipment, climate management, or even lighting – the first thing you need to know is your crop. The equipment needs to be selected and sized specifically for the crop you're growing, the climate that you're in, and your expectations for quality and yield. If you're a cannabis grower who wants to grow top-shelf material, you might want more control over the water nutrients you deliver and the climate that you create for your plant. But if you are growing wholesale, or if you are going to just sell your plants for extraction, then you may not need the same level of tech. Thinking about what your market is and thinking about what your production goals are will inform the type of equipment and the level of technology that you need.

The other thing is, what is controlling that technology? The grower is totally an under-appreciated element to the success of any indoor farm operation. You really need someone who has their eyes on the ground, who can help make decisions about what equipment to install, and who will pay attention to that crop and how it's responding to what you give it.

Automation controls and sensors are also invaluable tools that can help the grower understand what's going on to cause their plant to grow a certain way. From my perspective, as someone who focuses on climate, at least having a temperature sensor somewhere hanging in the greenhouse over the canopy can provide invaluable information about the changes that your plants are responding to. Beyond that, having a relative humidity sensor, having a light sensor and a PAR sensor actually measuring the light coming into your greenhouse is also helpful, especially for growers who are trying to give a specific quantity of light to their plants. A CO2 sensor can be helpful, if the grower is trying to manage carbon dioxide levels in the greenhouse. More growers are also starting to look at leaf temperature sensors so that they can control vapor pressure deficit more precisely. Having at least one set of the sensors inside the greenhouse over the top of the canopy can provide really indispensable information about the environment that your plants are exposed to over the course of their life.

For greenhouses, we often talk about low-tech, medium-tech, and high-tech greenhouses. A low-tech greenhouse might be a high tunnel, where you might have a ventilation fan, an irrigation system, and a temperature humidity sensor that is controlling the fans and turning them on and off, for example. A medium-tech greenhouse probably now includes evaporative cooling, maybe a light deprivation setup, more precise nutrient management, things like that.

A high-tech greenhouse could include air conditioning. We are talking to more and more people who are interested in air conditioning their greenhouses. The greenhouse effect is in full force and the sun is trapped inside that greenhouse. It can be incredibly energy-intensive going down that route. But again, if you are trying to create a very top-shelf product and still use all the benefits of sunlight, then maybe an air-conditioned greenhouse is worth the investment.

AB: Do you have any specific tips or cautions for someone who is considering getting started with one of these greenhouses with controlled environment technology?

NS: Some of this I’ve sort of touched on already, but the number one thing is to consider your market. Again, are you thinking top-shelf cannabis? Or are you thinking about extraction and wholesale, where maybe the quality doesn't matter as much as the quantity?

Number two is your climate. Being in a greenhouse, you are exposed to the changing environment outside. Although we are protecting the crop and we do have equipment that can control the heating and the cooling and the irrigation and the lighting, where you are located – in terms of latitude, longitude, if you’re coastal, if you’re in the desert – all of those factors related to climate are going to affect the equipment that you choose and also how your plant might respond. I'm of the belief that, for plants, sometimes what doesn't kill you makes you stronger; by having exposure to some variability in sunlight, in temperature, and humidity, maybe that actually can elicit some positive quality or yield responses from your crop. So, don't be concerned if you don't have the level of precision that an indoor grower can have, there might actually be some benefits to that.

Another tip that I want to give is to not be afraid of shading your crop. Some growers think that having the full intensity of light during that entire 12-hour daylight period of flowering is like ‘the more the better.’ But that is not necessarily the case. If you don't have all the other variables tuned in to those high light levels, such as your irrigation rates and your nutrient levels and your temperature, that sunlight might just heat up your crop unnecessarily. By shading the greenhouse, even just to 20-30 percent shade during the hottest and sunniest part of the day, that can really reduce the stress on your crop and can reduce the size of the cooling equipment that you need for your crop. So, you're helping your plant and you're helping your bottom line. The same goes for thermal screens at night. There's a lot of heat that can be lost from the greenhouse when exposed to a clear night sky, so having a thermal screen can both help to insulate the greenhouse and also prevent radiation from escaping, reducing your heating costs.

AB: Is there anything else of interest that you are seeing in the sector right now?

NS: One area that a lot of us see huge potential for in cannabis production facilities is the automation of very labor-intensive practices. So, whether that’s seeding, cloning, transplanting, harvesting, just all of those things that are usually assigned to humans that don't necessarily need a human touch. Moving plants from point A to point B can be done with conveyors and with other sorts of mobile racking systems that are already used prolifically in tomato production and all sorts of other greenhouse operations.

I think that's a major area of opportunity for the cannabis industry: figuring out how to customize automation and machines to help with those laborious tasks, so that the growers and the people who are working in the greenhouse can focus more on more productive things, like tweaking water cycles, nutrient recipes, and doing all the things that growers have fun with.

Nadia Sabeh, PhD, was speaking to Alexander Beadle, science writer for Analytical Cannabis. Questions and responses have been edited for clarity. This article originally appeared in Analytical Cannabis' Technology in Cannabis Cultivation eBook in December 2020. 

Alexander Beadle

Science Writer

Alexander Beadle has been working as a freelance science writer since 2017 and has covered the cannabis industry for Analytical Cannabis since 2018. He has also written for our sister publication, Technology Networks, and the cannabis industry consultant firm Prohibition Partners, among others. Alexander holds a Master's in Materials Chemistry from the University of St. Andrews, where he won a Chemistry Purdie scholarship, and conducted research into zeolite crystal growth mechanisms and the action of single-molecule transistors.


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