Can a person grow greens, in Maine, during the winter, without artificial heat?
The obvious answer to this question would most certainly be no. Outside, the weather is literally freezing and, of course, plants cannot grow in these conditions. Water may freeze inside the root and will not be able to get to the plant. Some of us in the THMS Garden Co. decided to look at this question, wondering if, by building a Hoop House, we could change the answer to this question.
We built a 12’ by 20’ hoop house for the plants to grow in. Our hoop houses are like the big green house, but mini, without any artificial heat. With a team of people, these hoop houses can be moved around the garden. Inside the hoop houses we assembled small hoops to hold row cover close to the ground.
Next, we conducted a series of experiments using probes that can measure and record temperatures at certain intervals. We placed one of these outside the house, two in the
hoop house with one under a row cover inside the hoop house. The temperatures were generally much colder outside, and warmest under the row cover (see page #6 for graph). The temperature without the cover was about 15 to 20 degrees colder then with cover.
Why was it warmest under the row cover?
There is something called the greenhouse effect. When sunlight comes through the walls of a greenhouse, it bounces around but is not able to leave the greenhouse. With a row cover, some of the heat in the greenhouse bounces under the cover. Under the row cover the heat is contained the best, but outside, with no cover, the heat is contained very little.
In both the hoop house and under the cover, we were able to keep the temperatures high enough to grow greens, even during those below 0 degrees nights. Right now we are growing some spinach, planted this winter, both inside of and out of the row cover.
The row cover spinach is growing much better. Even though the temperatures stayed very cold this Feb we did notice that growth picked up as the days became longer, despite the cold. So thanks to our greenhouse effect, our probes, and our healthy greens we have proven that it is, in fact, possible to grow greens in Maine during the winter, without any artificial heat.
-Healthy Greens Team