Three Ways to Heat Your Greenhouse In the Winter
Morgan Rogue 01.12.23
Year-round gardening is possible with a greenhouse. In some areas it’s almost essential to have one so you can start seeds, if you don’t have the indoor space to do so anyway.
Even when I lived in the high desert, I felt like my greenhouse was more successful than the plants growing outside.
A greenhouse offers the perfect atmosphere for a lot of plants to thrive, or at least get started.
When I got my first greenhouse I was under the impression that the greenhouse stayed warm even throughout the cold nights.
This is not true.
The first frost and every single one of my plants died.
A greenhouse doesn’t protect from the cold.
You need ways to keep the inside warm when there’s not enough sun and/or the temps are consistently below freezing.
If you are wanting to grow in the greenhouse year-round, how will it stay warm in the cold?
I was told to try filling barrels with water, the water heats up during the day from the sun and then the heat from the barrels dissipates throughout the night into the greenhouse.
The problem with this approach is, what if you don’t get enough sun during the days to heat up the water efficiently? And what if the water freezes because it’s consistently below freezing and the sun isn’t warm enough or out long enough to warm the water? The other problem is, this method doesn’t keep the greenhouse warm all night, especially in extremely cold temps. The heat dissipates pretty quickly and leaves the rest of the night at the whim of the below freezing temps.
I was also told to line the greenhouse floor with bricks. Which I did. The theory behind this is the bricks absorb the heat then they slowly dissipate the heat throughout the night. However, the same problem occurs here as with the water barrel problem; the dissipated heat simply doesn’t last long enough throughout the night. The bricks dissipate the heat then get very cold, along with the rest of the greenhouse.
Neither of the above methods was proven for prolonged heat in below freezing temps.
To sustain heat in a greenhouse, you’ll need something a bit more substantial.
Keep in mind, you don’t need the greenhouse to be super hot (unless you WANT to or NEED to), it just needs to be protected from freezing temps. So even if it’s being kept at 40 degrees, that’s okay! It’s above freezing.
Here are the best heating options for a greenhouse:
Wood stove
If you live in an area with abundant wood, a wood stove is a great option. It will need to be vented just like it would be in a home. Plants and other flammable items would need to be kept within safe distance from the wood stove.
When the sun sets you’ll need start filling the wood stove and begin heating the greenhouse. At around midnight-ish, you’ll need to go in again to fill the wood stove and get it going again for the rest of the night.
If you live in an area like Alaska where you don’t get much sun during the winter, you may need to fill it more often. It depends entirely on your area and how warm/hot you need to keep your greenhouse. I would say during the first week, go out more often to check on the temp and examine how often you’ll need to pack the wood stove.
Propane
Propane was an efficient use of heating our greenhouse when winters only lasted a couple of months.
Depending on how big your greenhouse is and how hot you want it, when you hook up a Mr. Buddy Heater to a 20lb propane tank, it can last a couple days of going constantly. Of course, this probably sounds expensive, but if you are turning it on and off, it will last longer.
If you’d like to use a larger propane tank hooked up to a back wall, these have temp controls on them so they will turn on and off on their own.
Rocket stove
The rocket stove also uses wood, but it’s usually smaller pieces of wood and it burns very fast and efficiently. If you make the rocket stove with brick, it will be even more efficient and that will be consistently dispersed among the brick.
Just like the wood stove, you will need to fill the rocket stove with wood sticks as needed. This will need to be an experiment.
People can get creative with heating their greenhouse.
I’ve seen people build mud ovens in their greenhouse, compost, geothermal, some even have their chickens inside of their greenhouse.
Keep the heat in by putting bubble wrap on the windows and seal up the cracks really well.
Depending on how hot it gets in there, though, you may still need to crack a window for proper ventilation.
Tons of options out there. Find the option(s) that works best for you and your situation.
