Challenges of Year Round Greenhouse Gardening
"How can I heat MyOwnGreenhouse to grow year round?"
This is a common question we get and it’s a good question, one that many of us Zone 3 and 4 gardeners would like an answer to!
There are some simple ways to get enough heat to extend the growing season by about a month on either side of summer. In Alberta, Canada (latitude 53 North) this means growing from April to October. For us, that means we have 50 gallon dark rainwater barrels in our greenhouse and paving stones on the ground.
The stepping stones and the black barrel absorb radiant solar heat throughout the day, storing it in the water, and slowly release the heat throughout the night. This helps reduce fluctuations in overnight temperature drops. It takes a lot for that big barrel of rain to freeze!
We recommend keeping a removable lid on your barrel so you can access the water and at the same time keep the rodents from drowning in it and keep the mosquitoes from laying eggs in it. Be sure to drain the water out when you clean everything up at the end of the season.
Year round growing, though, that's a much bigger challenge.
It is very difficult for amateur gardeners to grow year round in a small greenhouse because you have to manage not only the heat, but also water and the wavelength of light the plants are getting.
This means both a heater and a fan to circulate the air around the space (enough to move the air but not too much so the plants don’t get damaged), plus grow-lights for the October through March period when our northern sun rays aren’t long enough for growing. You will also need a way to get water to the greenhouse so it doesn’t freeze.
Some gardeners resort to extreme measures like building a mini-greenhouse inside the greenhouse by wrapping the whole thing in bubble wrap or solar pool cover. Some people excavate 6’ deep to try and take advantage of some geothermal heat (piping warmer air from below the frost line and circulating it up into the frozen air in the greenhouse).
Though there are many greenhouse heating companies, but we have't yet found one that specializes in personal greenhouse heating (just commercial).
Many nurseries have used 110V hot water heaters to heat either raised or ground beds. Roots are more temperature sensitive than tops of plants. This link provides the basics of a system: https://farm-energy.extension.org/root-zone-heating-systems-for-greenhouses/