In No Guff Vegetable Gardening we tell readers that cold frames are a simple way to create a microclimate in the garden.
Here’s what we tell readers in the book No Guff Vegetable Gardening:
A cold frame is nothing more than a simple mini-greenhouse heated by the sun. In its simplest form, it can be an old window set atop sides made from boards (or even straw bales).
Cold frames serve three purposes for the vegetable gardener:
- Provide a warm spot to grow seedling transplants while it is still too cold outside
- Protect early in-ground crops of greens such as lettuce, arugula, and spinach while the ground outside is still frozen
- Shelter fall crops of greens
Ideally, the cold frame faces south, with the back wall slightly higher than the front, so that the window is on a slope to catch more sunlight.
Because the sun heats it, it cools down when the sun sets, though it doesn’t become as cool as the surrounding garden. That’s because a cold frame also traps some of the heat given off by the ground. Covering it with a blanket or tarp on very cold nights will keep it slightly warmer.
On warm, sunny days a cold frame can actually become too hot, so it is important to prop open the window to let out some of the heat (or invest in automatic vents).
Steve says: My Dad, Bob, had an open-backed cold frame that he set up in front of a basement window. On cold nights, he left the window open to keep the temperature in the cold frame above freezing.