Can you grow tomatoes in a heated greenhouse during the Maine winter without issues?
Question:
I am writing to inquire about growing tomatoes in a heated greenhouse during the winter in Maine. The greenhouse can be heated to optimal growing temperature, but I was wondering if there would be enough sunlight to have fruiting plants without supplemental lights. Would the shortened daylight just increase the amount of time needed for fruiting, or would the lack of sunlight cause the plants to not fruit at all or minimally?
Answer:
So, it is possible to grow greenhouse tomatoes all winter in Maine in heated greenhouses (the largest example perhaps being Maine’s own Backyard Farms), but it really does require supplemental lighting. You are correct that winter daylight in Maine just isn’t enough on its own, with day length, light intensity, and potential snow cover on the greenhouse being issues (thought that would be mitigated by it being heated). Tomatoes need something like 650 foot-candles of light for a minimal crop, with a single 1000W greenhouse lamp giving off about 600 over a roughly 10×10 area. You probably would eventually get flowering from tomatoes running on pure winter daylight in a heated greenhouse, but it would be slow and sparse.
I would also highlight that supplemental lighting in greenhouses gets extremely expensive (especially at the moment, when Maine may be facing rising electricity costs in the near future)–it’s usually prohibitive for a home grower, especially given the crop size, and typically used only by commercial operations. If you do decide to experiment with the supplemental lighting, keep an eye on the temperature in the heated greenhouse, as the two working together can get quite hot. And in the heated, closed, moist environment, you’ll need to think about pests and pathogens that thrive on greenhouse conditions, so be on the lookout (see the MOFGA links below for examples).
I will include a few nice MOFGA (Maine Organic Farmer and Gardener Association) links regarding various ways of winter growing tomatoes in ME if you are interested in a broader view of the topic:
Tomato Production in Hoop Houses
I should note that a heated greenhouse without supplemental light can be a great place to grow low energy intensive crops through the winter like brassicas, leafy greens, root vegetables, and herbs, so don’t give up on the greenhouse use if you’re interested! Greenhouses are also fantastic tools, of course, for extending the growing season by pushing the starting and ending margins, even if you don’t grow prized tomatoes all winter.
Happy gardening.