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Greenhouse 101 with Andrew Cook: Heating Your Green House

Andrew Cook of European Garden made a special trip to my garden to help me set up a greenhouse.  Andrew explained to me what I should do to keep my greenhouse heated in winter.  Here is an excerpt from our conversation.

Allen: When heating a greenhouse, a hobbyist greenhouse, what are the things to consider?

Andrew Cook: First of all size. How big is it? How much do you want to heat it up? The second thing is what temperature is desired? Usually the ideal temperature is about 52 degrees, orchids need about 62 degrees.

Andrew Cook: So the BTU's, which is what a greenhouse heat is generally expressed in, could be anywhere from 10000 to 20000 BTUs for a small greenhouse. Usually what we recommend is if it’s going to be cold during the night but not during the day, you might just go to your local home center store and buy a 49 dollar oscillating heater

Allen: Just to take care of those few nights when the temperature drops down. But what if you live in Minneapolis?

Andrew Cook: Then you’re going to need something much more permanent. And it depends on how much work do you want to go through. The heater that we installed here, the big red bulk heater, that’s a 19000 BTU heater you can get at W Granger. It’s very good at heating a greenhouse, but it does require 220 volts. So you an electrician might need to install it. So maybe for some people it’s more convenient to buy 2 general home space heaters and use those.

Allen: In the past I’ve used those heaters that are on wheels that actually look like radiators, where the oil heats up in them. It’s what I had in the lathe house and just kept the temps above freezing, which was ideal for me keeping my citrus plants as well as agapanthus and agave and that sort of thing.

Andrew Cook: The only drawback with those heaters is the amount of time they take to heat up.  The blow heaters raise the room temperature faster.

Andrew Cook: If you have a greenhouse bigger than 150 sq ft you may need to look into propane heaters.  It gets more complicated at that point because of the need for a gas line.

Allen: The heater we have in my greenhouse actually has a thermostat attached to it so its going to kick on at the appropriate time and then switch off.

Andrew Cook: Correct there’s a switch in the back. We put your heater on a stand, not on the ground.  And placed it against the back wall, in a spot that’s easy to get to.   And just have the heat blow through the whole greenhouse.

Allen: So I feel like I’m prepared for that coldest night in January now.

Andrew Cook: Yes you are. The only thing we'd add to this greenhouse is hang up some lights. Those can be hung up you'd need some damp proof, fluorescent light bulbs and we have some hooks that can also be provided.

Allen: Well I though that I would, because in the winter we have reduced light.   I thought I would put some lights in here later in the season when I start growing some seedlings for the spring garden.