Heating the Greenhouse1
When I was growing up my mom always had a countdown to spring. I’m not a fan of cold weather, or snow, or the cold-meets-muddy mess that is early spring in Michigan. For all those reasons I always joyfully joined into the countdown. And for all of those reasons I was always sorely disappointed. Here’s why: Mom counted down to The First Day of Spring… as in the little square on the calendar that tells us the day of the astronomical vernal equinox has arrived (March 20 this year). In Michigan, that usually means it is still cold, possibly snowy and muddy beyond belief. Once I became a teenager and wised up to all of this, I vehemently refused to participate in the countdown to avoid the imminent disappointment. I’ve learned that it’s best not to expect spring until May.
Expecting that warm weather won’t be here until May has implications for our greenhouse. In order to plant by the phases of the moon and have my transplants ready for the garden by the time our last frost date passes I have to start seeds as early as next Monday (March 11). We don’t have room in our tiny house to store the thousands of seeds I plan to start in March and April so they need to go elsewhere. The greenhouse is naturally a good candidate. This time of year there should be plenty of light to keep my seedlings happy during the day, however, the temperature is still well below freezing most days. We need a heater.
Enter my desire for low-cost, sustainable processes. We have an electric space heater in the greenhouse which did a fine job of heating our 6’ x 6’ space this fall. I was hoping to find something a little more sustainable – or at least less expensive – to do the job. Here are some of the things I considered (solar powered heater, terracotta pot heater and rocket stove) :
Of all the options I decided to try the terracotta pot heater. Online reviews from other users seemed to indicate that the heater didn’t give off as much heat as they had hoped but it still “worked.” Here’s the idea: A flame or energy sources dramatically heats the metal core which then radiates out through the terracotta. One person said it could be used to heat a small room. A 6’ x 6’ greenhouse is a pretty small room so I felt optimistic. Plus I already have plenty of pots so materials wouldn’t’ be very costly. Materials include:
- Two terracotta pots (10″ and 12″)
- Heat bulb
- 2” threaded bolt (1/2 inch diameter)
- 8 washers
- 4 bolts
I decided to use a light bulb instead of a candle because I felt the energy would be more consistent and then I wouldn’t have to buy a supply of candles. (If I ever needed to use the heater with a candle instead of a light bulb, that would still be an option.) We’re preparing for chickens so I recently bought a pack of two 250W heat bulbs. Using a lamp I already own, I tested the heater by placing a large pot over the bulb. Presto – heat!
Next I went to Home Depot and bought the bolt and a handful of washers and nuts. I used the bolt to thread the 10” pot inside the 12” pot.
Then I setup the lamp (used an extension cord from the garage), surrounded it by 6” pots placed upside down (like a tripod) and set the threaded pots over the lamp (resting on the 6” pots).
In very little time the pots began to heat up – a lot!! I even burned myself on the bolt once. But alas, after several tests I determined that the heater at best was making a 1-3* difference in the air temperature of the greenhouse. And that at best difference was happening in the afternoon when I need it least. At night time (when I need it most) there was no measurable difference at all. Even if I had two or three of these bad boys, I don’t think it would help.
Oh Mr. Sun
The good news is that since I was monitoring the greenhouse temperature closely for several days I noticed that the sun has reached a point in the sky where it is adequately heating the greenhouse during the day. Today it is 100+ degrees in there with just solar heating! So long as we continue to have moderately sunny days, I think I’ll be able to get away with letting the sun keep my plants warm (above 60*) during the day and using the electric heater at night. If time allows, I’d like to try making a small rocket stove to use at night. No promises there, but if it happens, you can be sure that I’ll share my findings with you.
Does anyone have tips for how they heat their greenhouse? Any creative ideas you’d like me to try?