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The Science of a Greenhouse
A greenhouse is any building or structure that is designed to capture the heat and light from the sun for the purposes of growing plants. Greenhouses allow for more precise control of the environment in which plants grow.
Generally speaking, greenhouses have a skeletal structure which can be made out of hard plastics, wood, metal, and more. This skeletal structure has large gaps through which sunlight can travel. These gaps are covered by a translucent material — typically glass or plastic.
The basic principle that allows greenhouses to control their environment is very similar to the greenhouse effect. Light passes through the translucent material in the greenhouse and is converted into heat. The heat is then trapped inside the building and cannot leave.
There are a large variety of greenhouse types, from the humble polytunnel to Victorian-era glasshouses to modern greenhouses and hybrid greenhouses.
What You Should Know About Greenhouses
Greenhouses are very sophisticated machines and how well they run depends on how well they’re designed and built. Shane Hutto
I should also mention the different types of components that are involved in making greenhouses.
And finally there’s terms related to the management of a greenhouse. Crop structure is one such term. Labor flow is another big one. Greenhouses are very sophisticated machines and how well they run depends on how well they’re designed and built.
Hybrid greenhouses tend to work better in areas where you have light high in the sky for most of the year. In northern latitudes that don’t have a lot of light in the winter, hybrid greenhouses aren’t particularly useful. Essentially hybrid greenhouses are useful in areas where you expect a security risk or a legislative body wants you to have something more secure than a glass or plastic wall.
I would say that hybrid greenhouses have better insulation properties, but I wouldn’t say that that’s a major selling point for them. We can get pretty high R-values in a greenhouse, especially if we’re under glass. We have energy retention curtains and things like that if we’re in a scenario where we’re worried about utilities or trying to save on operations costs.
Greenhouse height also impacts your ability to control the environment. One of the big rules in greenhouse construction is that the taller your greenhouse is, the easier it is to control your climate; the extra height provides a huge barrier of air between the crop and the greenhouse exterior. The height difference will allow you to control your environment much more precisely. In short, as you go from a small, entry-level greenhouse to a large, full-scale high-tech greenhouse, you’re going to see the height go from 10 to 12 feet to the truss all the way up to 20 to 25 to the truss.
We also make sure to build the greenhouses to the local building codes. If you’re in an area that doesn’t require a super-sturdy structure, but you still want it tall, then it might not be necessary to make the greenhouse beefy. If you’re in an environment like the mountains of Colorado where you have to design for huge snow loads on the roof and wind loads on the structure, then you’re going to have a much beefier structure. We build the structures for the environment.
As far as companies go for the different categories, you can find them pretty much everywhere. Some of the good manufacturers for low-grade greenhouses, in my opinion, would be Rimol or Nexus. When you get into the mid-grade greenhouses, you’re probably looking at a GGS or a Rough Brothers (pronounced Rao). With high-grade greenhouses, you’re looking at Havecon, Bom Group, or something in that range.
Editor’s Note: Terms such as “low-grade” are meant to describe low-tech, not low quality. The aforementioned greenhouse manufacturers are some of Shane’s preferred manufacturers, but there are many more high quality manufacturers out there.
Structure matters, sure, but the technology that goes into it matters as well. Every greenhouse manufacturer will sell you all the equipment that goes inside the structure. That may or may not be a good decision. If you really know what you want and what you’re ordering, then a greenhouse manufacturer is probably going to give you a good deal.
However, realistically speaking, [some] greenhouse manufacturers don’t know enough about cannabis to understand what the right equipment is and how to design the greenhouse around it. I would use a greenhouse manufacturer to put up the structure, and then I would go to the technology’s manufacturer, a good consultant, or hydro-stores to get the right equipment for the job. That’s the best way to approach it.
Because it’s difficult to find a solid resource, every greenhouse manufacturer will tell you that their structure is the best, and that their structure is the best for that crop, and that their structure can give you the best. Most of them embellish a bit.
Editor’s Note: Growers Network is building a centralized resource for this kind of information. If you are interested in contributing to our research, please contact us at [email protected].
The Greenhouse Market
Nobody wants to invest a million dollars in a greenhouse and 5 years later see it rusted to hell.Shane Hutto
There’s a ton of different companies in the space. The best approach to find one appropriate for you is to start going to greenhouse tradeshows. There are a substantial number of shows every year that are centered solely around greenhouses. One of the best trade shows in my opinion is the Canadian Greenhouse Conference. It’s just across the border in New York if you’re flying to Buffalo. Another big trade show is Cultivate in Ohio. It’s a little more nursery centered, but there’s still a ton of greenhouse activity there. Greenhouse Grower Magazine also puts on a lot of different events that are centered around greenhouses.
When you start talking about environmental technology, I definitely would look at Delta-T Solutions. Whether it’s an indoor grow or greenhouse grow, they’re top level. If you want an automated greenhouse, Havecon seems to be one of the most sensible companies, in my opinion. They operate the best products for the money.
One greenhouse manufacturer I want to mention is Harnois, a French company. They make some really good, sturdy greenhouses that are middle of the road on costs. For the structures, they use oval tubing instead of square tubing, which adds a lot of strength to the structure. GGS is another big manufacturer. GGS builds some quality structures that are nice and sturdy, although they use square tubes. Rough Brothers, pronounced Rao Brothers, isn’t a bad one. They make a quality structure. That said, they’re sort of the low-end for what we do. If we want to get into truly low-tech greenhouses, I would probably look at Rimol. They build some of the easiest to DIY greenhouses. DeCloet also builds a nice middle of the road greenhouse. Nexus greenhouses are on the lower-tech side of things. Nexus greenhouses don’t get very tall, so they tend not to be my favorite. I’m going to be a proponent of the height of a greenhouse.
Beyond that, there’s hundreds of different companies out there. They’ll all tell you that they’re the best and that they have what you want. Understanding what you’re buying from a greenhouse manufacturer is difficult.
I’d also like to think that most growers enjoy the challenge of improving their skills, as greenhouses are more complicated than indoor growing.
There are a few reasons why you should not choose to use a greenhouse. When your local government is worried about security, a greenhouse is seen as a liability. Another reason not to get a greenhouse is if you’re growing in an area where you see powerful forces of nature, like high amounts of hail or destructive winds. We can build greenhouses rated up to 110 mph wind-load, but if you’re supposed to be rated for 150 mph winds you may want to pick another building type.
Beyond that, I would say there is no environment where we can’t build greenhouses. There’s greenhouses in Antarctica and there’s also greenhouses in Iran in the middle of the desert. We can build in all extremes. The most difficult, extreme place to build is a really high-humidity area. Your costs are going to go up dramatically.
If you’re looking to build a new building, we can build a greenhouse for the same cost that you could build an indoor grow. Now if you’re retrofitting a building, that’s a different story, and the costs on that will vary. But if you’re doing new construction, I can probably build a greenhouse for about the same price as an indoor grow, including the same technology.
When you factor in the sun’s light, your cost of operations goes down by about a half.Shane Hutto
Then the question of costs goes to operational costs. When you factor in the sun’s light, your cost of operations goes down by about a half. That’s really what’s attractive about a greenhouse grow. Now, to clarify, there’s a higher learning curve in a greenhouse: understanding seasonal variances, understanding the difference between the maximum light intensity you can get under the sun, learning how to make those daily adjustments based on what is happening outside, and more. It’s a steep learning curve.
There’s a lot of people who believe that the quality of indoor-grown cannabis will always beat greenhouse-grown. Personally, I have experienced far better product out of greenhouses than I have out of indoor grows. As far the market is concerned, the indoor game is still top-dog, but if you have a greenhouse dialed in, you can see faster, larger growth in your plants.
You want to consider the lead time on the structure. Typically you’re going to see 12-16 weeks for delivery, and then depending on the structure, it could be 4 to 12 weeks of construction. If you’re on a deadline, this is an important factor to consider.
A lot of greenhouse manufacturers don’t do their own construction. Many of them will just drop the structure on-site and you have to either find your own contractor, or they have one that they recommend. Without a contractor, some of these structures get built and halfway through they fall over.
Your next big pieces are your lighting and your irrigation. Lighting a greenhouse is different than lighting a warehouse. You don’t want to hang a bunch of things that are shading your plants during the day while the sun’s out. Because of this, we try to stick lights into the trusses and crossbeams, which is where your equipment will hang. You don’t want large reflectors. A commercial fixture is where it’s at.
Placement is going to be done with calculations and a spreadsheet. Unlike a standard grid in a warehouse, your trusses may not be distributed evenly. In addition, your spans are much wider, and your lights are much higher up.
Essentially, in a humid environment I’m going to suggest a sealed system, where you’re not exchanging a lot of air with the environment. Any time you bring outside air inside your greenhouse, you’re essentially changing your humidity levels. Because we don’t want your humidity to run too high for cannabis, we seal up the greenhouse to bring in very little outside air. We then treat all the air inside and recirculate it through a closed system. That’s going to help with odor control as well. Whereas, if you’re in a dry environment like Arizona or Colorado, then an evaporative cooling pad makes a lot more sense. We aren’t worried about fighting humidity above 50 or 60%, generally.
When it comes to temperature, I would rather build a greenhouse in a cold area than I would in a hot area. It’s easier to heat a greenhouse in the winter than it is to cool a greenhouse in the summer.
As far as heating goes, floor heating is a great method. It’s a drier heat and it tends to perform much better than other heating sources. Floor heating can be centered right around your root zone, so that you’re not just getting heat to the canopy, but also to the roots. Because roots like warmer temperatures, the root system will grow faster. The heat on the bottom also creates a turbulent air that rises through the canopy, keeping the crop metabolically active. There’s a lot of advantages to floor heating.
The Technology of Modern Greenhouses
For automated irrigation, I really like the Priva system. Priva’s systems tend to be the best at working in conjunction with the environmental system and comparing graphs from the environment against the irrigation, plant size, and whatever other parameters that it’s set to track.
An example system, image courtesy of Priva. Click for larger image.
Dosatron is probably the most widely used irrigator, but in my mind that’s in the low to mid tech range. On the high tech side, I’m using Priva irrigators and UV sterilizers. As facilities get higher-tech, there’s more water recirculation coming from the runoff of the plants. Right now, we’re creating a water-neutral facility, and because of the sterilization procedures we’re taking, we won’t face the risk of water-borne plant pathogens.
Priva injectors are computerized. They can be set up in multiple ways, but essentially you have 4 injection ports, an acid, and a mixing chamber. Your concentrate gets pulled from its tank, goes through a mixing chamber, and then a computer checks to see that it matches the EC and pH that you want. Then the water gets sent out. That computer has the ability to make 50 different recipes, so if you want a different fertilizer for each irrigation zone you have set up, you can have it.
Now that said, the technology definitely isn’t cheap. It’s not something that’s going to be for everybody. But if you’re in a high-tech facility that you spent some big money on, then you’re probably not going to balk at top-notch irrigation and environmental systems. The pricing generally starts around $40,000 or $50,000 and can easily reach in excess of $200,000. If you want a cheaper environmental controller, you might try Damatex. They’re like an entry level Argus, in my opinion.
When it comes to dehumidification, it really depends on the system. Realistically, the right dehumidification system in pretty much every case is going to be based off of a boiler and a cooling system to overcome the heat from the boiler. This creates condensation to draw water out of the air. One company that comes to mind is Delta-T Solutions. They probably have the best dehumidification system that I’ve seen. There are some standalone units that we use as well. One company is called DryGair. They’re based out of Israel. We also work with an Italian company called Vifra.
On that note, we should talk about air conditioning. You definitely don’t want conventional air conditioning in a greenhouse. We don’t want to have thin coils with ducting running all over the place. In high humidity areas I recommend a sealed greenhouse and a hydronic chiller system. It’s “air conditioning” but it’s a more efficient technology, and in order to function properly, the greenhouse has to be sealed off or have limited air exchange. A hydronic chiller system runs chilled glycol or another non-conventional refrigerating fluid from outside of the building into it, carrying heat back outside. Delta-T Solutions also designs hydronic chiller systems.
Editor’s Note: There are a range of other options out there for environmetal controls. Delta-T is Shane’s preferred company for environmental control.
One of the more recent innovations we saw is an automatic leaf picker. They’re calling it a de-leafer. It’s essentially designed to remove leaves from the bottom of your plant. Because it’s a robot, it uses an infrared eye to inspect each plant. All you need to do is set the parameters in the computer once. If you wanted to take the bottom two feet of leaves from a plant and leave all the stems, you program the de-leafer. It can run 24 hours a day just moving around, checking every plant in the building. This significantly reduces labor costs. I approached Priva about the technology, and I’m told that I will have my opportunity to assist with development sometime in early summer of 2017.
There’s a company called the ISO Group, and they’ve developed some really interesting technology in conjunction with the University Groningen in Holland. For example, they have an automatic cuttings machine. You stick a whole plant or a branch in, and it’ll cut the plant apart and automatically create cuttings for you.
One of the other things that really comes to mind is tissue culture. There’s machines now that can auto-sample tissue. That means you can put in a branch or piece of the plant, and the robot will take a pinprick, enough for a handful of actual plant cells. It takes those cells and transfers them into tissue culture for you. That’s the start of your tissue culture. It’s very expensive, like $150k.
ISO Plantsampler can take small samples of plants automatically.
One of the big things I look forward to in the industry is developing tissue culture and clean genetics. I’d like to see certified disease-free plants.
On the lighting side, there’s a lot of advances in LEDs. A lot of LED companies are making a run at cannabis. One LED company that I expect to make an impact in the market is called the Oreon. They’re a Dutch company. Their LED is actually water-cooled, and you can recirculate the water for under-bench heating as a free source of heat from your lights. Plasma lights are typically not used in greenhouses because you get a lot of the UV spectrum out of plasma. You already get enough of that from the sun. As a result, you generally don’t need to supplement with plasma. I’ve also seen guys experimenting with ceramics, but I don’t have a lot of feedback at this time.
I would say that most people who use a DIY or a prefab greenhouse will come back years later and want a nicer structure. Hopefully by that point they’ve made the money to pay for the new structure.
A typical polytunnel
The big concern is that their polytunnel blows away or gets destroyed. Hail can go right through some of those DIY structures.
The other worry with DIY greenhouses is that they can be affected by local construction laws. DIY Greenhouses can be seen as temporary structures, so local ordinances can shut you down for lack of permanency. Additionally, once you build a greenhouse structure, you fall under agricultural regulations. In most states that means the Department of Agriculture can come and inspect your operation. State troopers can also come and inspect your operations.
Realistically, I can see a model where warehouses will be converted to cloning and propagation, with some vegetative growth, and greenhouses would be used for flowering. There’s some areas where we won’t see warehouses disappear due to laws or environmental conditions.
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Want a consultation from Shane for a grow operation?
The best way to find Shane is through his website hort-solutions.com. There’s a contact form on the website. You can find the office phone number on there. Shane’s secretary can set up an appointment. You can also email [email protected] and somebody will take care of you.
- Horticultural Solutions — Consult with Shane Hutto on your own greenhouse.
- Priva — Horticultural Automation
- Delta-T Solutions — Environmental Control Systems
- Dosatron — Automated Irrigation Systems
- DryGair — Commercial Dehumidification Systems for Greenhouses
- GGS-Greenhouses — High-Quality Greenhouses
- Want to see a major greenhouse in production? Check out Episode 1 of Canna Cribs.
Do you have any questions or comments?
About the Author
Hunter Wilson is a community builder with Growers Network. He graduated from the University of Arizona in 2011 with a Masters in Teaching and in 2007 with a Bachelors in Biology.