What does CO2 do?
To farmers, the most important role of CO2 occurs after the gas molecules have entered the photosynthesizing tissues of plants via passive diffusion through pores in the leaves.
This is important because the relative amount of CO2 to other growth factors can have significant (even staggering) effects on production levels in indoor agriculture settings.
A common limiting factor
The reason for this is that CO2 is one of the most common limiting factors for indoor growers. And as we all know, sometimes raising or changing the limited factor can greatly increase output of a process.
Say you’re making sandwiches for lunch. You have the lettuce, tomato, and ham for five sandwiches, but the bread for only four. You’re most of the way to five sandwiches, but missing only two pieces of bread.
In a greenhouse, the lettuce, tomato, and ham could be your nutrients, light, and water. CO2 is very often the bread. And it’s usually much more than just a sandwich that’s being wasted. Usually the gap between the limiting factor and the production capability that exists were that limiting factor removed is somewhere between fifteen and twenty-five percent production.
This means that growers who have all other plant needs in excess (which is most) could increase the production of their greenhouse by fifteen percent if using CO2 enrichment.
Why wouldn’t you use CO2 enrichment?
“Seventy-five percent of indoor growers should be using CO2 enrichment,” says Dr. Nate Storey. So what about that other twenty five percent? When is CO2 enrichment a bad option?
The benefits of CO2 are neutralized when you are growing outdoors or partly outdoors, or if there is some cost-increasing factor makes CO2 enrichment un-economical for you. (That factor might be very high natural gas/propane prices, for example.)
CO2 enrichment is still often underutilized, however. For the benefits it offers, CO2 enrichment can be quite inexpensive.
There are two main techniques used to supplement CO2.
1) The first is injecting pure CO2 from canisters. This is very rarely cost-effective, however. The most likely reason that people started doing it in the first place is that it’s a low-profile way to supplement CO2 for people with too much money in their hands and a reluctance to show too much electricity use… if you catch my meaning. But anyone who is aware of the other CO2 enrichment option will forgo using straight CO2 because it’s so expensive.
2) The second way is to use a generator run on natural gas or propane. If you have access to a natural gas line, then this is probably the best option for you. (Depending on the price of natural gas in your area.)
To put the two options in perspective for you, let’s take our greenhouse here in Laramie, which is a 2000 square-foot high tunnel. To supplement CO2 in that greenhouse with normal ventilation and no special circumstances, we could expect a estimated cost of $2.00-3.00 per day in natural gas use. In comparison, a hundred pound CO2 refill would cost you about $70 and would be used up in about a week. That’s three or four times as much, and might not be worth the increase in production from enrichment.
What is the increase in production worth, anyway?
The answer to this will vary depending on the cost of natural gas or propane for you, as well as the crops that are in the space you’re enriching.
As an example, let’s say that you’ve got an operation like ours in a twenty by hundred-foot high tunnel. You’re using about halfof your five hundred ZipGrow Towers for greens, and the other half for herbs, and producing about 200 and 100 pounds per week, respectively. (And that’s conservative.) At roughly $4 per pound for greens and $20 per pound for herbs, you’re making $800 and $2000 per month already.
Now spend three or four hundred bucks on a generator and a few bucks a month for natural gas, and you bump up production by at least 15%. That’s thirty and fifteen pounds of greens and herbs, which you sell for $120 and $300. Already in the first month you’ve made back the initial investment. (As a note, this type of ROI is based on ZipGrow production estimates.)
So maybe you’re thinking, “if I supplement CO2 at a higher concentration, then I can get more and more production out of my plants, right?”
Well, no. Even if all of the other plant needs are met in excess, plants have a threshold of what they’re able to do. Thinking that they don’t is like saying, “If I feed my buddy Tom a hamburger and he runs fifteen miles, then if I feed him ten hamburgers, he’ll be able to run one hundred and fifty,”
Well, probably not. Tom is just a regular dude. And your plants are just regular plants.
Many studies have been performed on CO2 levels and plant production, and the general consensus is that the curve of improvement tables off around 900-1200 ppm, depending partly on the crop.
Take advantage of CO2
Ready to test out CO2 enrichment?
As we’ve seen, CO2 can bump up the already high production level of a vertical ZipGrow system to something that’s downright impressive.
Why wait to start growing more? You can find CO2 generators online or at the Home Depot or Lowe’s in your area.