All right, you oughtta like this one! We have our data on our late season greenhouse experiment that we conducted this year! The question at hand? Is it “worth” operating a cold climate greenhouse, with heat, for several more weeks than you would typically be able to achieve?
For the 15 second recap, we decided to operate our greenhouse about three weeks longer than we “normally” would this year. Our greenhouse is insulated with UV rated plastic, making it airtight and able to achieve some “low grade” and relatively inexpensive heating using space heaters. We heat to minimal temperatures (45F), mostly just to keep frost at bay. We heavily use this ability in the spring to help us raise our plants, but we wanted to see if it could also benefit true season extension purposes.
If you’re new to greenhouses, most people “roughly” estimate that you get about two weeks of season extension on each side of the season with them. This might not “seem” like much, but it turns a three month growing season into a four month season. Our first frost is typically September 1st, meaning we “usually” shut down our greenhouse around the 15th. Beyond this time, you really have to use external heat to ward off frosts and to generally maintain an environment where your plants (typically “warm season” crops) are growing.
Our crop of choice for this experiment was tomatoes, with the hope being that we could “eek out” several more pounds of fresh, heirloom grade tomatoes by doing this. We harvested “most” of our ripe tomatoes around mid-September, so we’d get a fairly good idea of what matured in the coming weeks. (Plus, this allows the plants to focus entirely on maturing green tomatoes.) Tomatoes are a “high value” crop to us, which we’d estimate at around $7/pound for fresh, lovingly grown quality tomatoes.
We won’t leave you hanging. We weren’t sure what to expect for the results, but the result of our experiment was decently effective. We’re not sure if we’ll continue to practice it, but we did see a “net positive” result.
Our experiment period was from September 15th through October 5th, a period of 20 days of season extension. During this period, it took us 107.12 kilowatt hours to heat our greenhouse. Translated to cost, at our current rate of $0.272 per kilowatt hour, we spent $29.13 heating our greenhouse during our experiment period.
Now, for the meat and potatoes, so to speak. Our total harvest of cherry tomatoes (some of which were ripe prior to our experiment) came in right at about 6 pounds. Our full size tomato harvest, none of which were ripe at the beginning of our experiment period, came in right about 4 pounds. So, we saw a total of 10 pounds of ripe tomatoes, largely due to our season extension experiment.
Knowing these values, we can assign a “value” to our experiment. If we estimate $7 a pound for heirloom grade tomatoes, we produced about $70 worth of crop with roughly $30 worth of input. So, technically, we’ve “proved” that such an effort can be potentially valuable.
We have some other pertinent thoughts on this experiment. We definitely noticed the “cost ticker” rising the further away from our last frost that we got, which is why we ultimately terminated the experiment. This is the opposite of what we experience in the spring, costs went from “cents per day” to “dollars per day” quite quickly. Our plant health also started degrading quite quickly, likely due to the fact that we had halted fertilization. But, also, heating against mid 20’s Fahrenheit is not without issues, it’s difficult to achieve “uniform” temperatures in a greenhouse. Also, this works for “higher value” crops, but would be less effective with “lower value” crops. It would make zero sense to do this with, say, lettuce since that lettuce could likely survive mid-20’s anyhow! Lastly, there’s obviously some seasonal dependence to this. We’ve had seasons with feet of snow in mid-September and clearly, these things could greatly influence results.
This effort also confirms what we all ready knew from our spring season experiments, that’s its not super feasible to heat against increasingly cold temperatures. While it may be “technically possible,” it’s less so “economically feasible.” While, sure, we could maybe choose a more efficient or less expensive heating mechanism than electricity, BTU’s always have relatively high cost. There’s an economic limit and preclusion to how far we could take this experiment, especially once we start diving into temperatures in the teen’s and single digits. The scale of financial efficacy dives down very quickly, based on outdoor temperatures. Put another way, it’s economically more feasible to justify “raising your entire garden” in spring than it is “maturing a few tomatoes” in fall.
But, we were somewhat surprised by the results. We honestly expected something around “break even,” absent any data. As for why we might not practice it in the future? We can also ripen our tomatoes off the vine, for practically zero additional cost. We only need to lay out our unripe tomatoes in room temperature, where most of them will become usable. We definitely “prefer” vine ripened, but I don’t think we perceive nearly $30 in additional value from “on the vine” ripening in this case. In some ways, we’d prefer the speed and maturity levels we can achieve via “off the vine” ripening.
Nonetheless, we do figure that things like this are part of the reason you all see value for us being in this space. We don’t see people doing these kinds of experiments, talking about the brass tax of input cost and economic gains of growing in cold climates. It’s important to know so we can make appropriate decisions as cold climate growers. A lot of us wonder, but we try to pursue the data and results as best we can.
Let us know what you think!
