Temperatures can vary widely in spring, potentially exposing your newly planted tender garden plants to freezing temperatures overnight. The same is true in the fall. How can you keep your plants safe from Mother Nature’s whims? Cold frames could be just the answer for protecting your vulnerable plants and extending their growing season.
What are cold frames?
Think of cold frames as miniature greenhouses sitting low to the ground. Covering two or three garden plants at a time, these bottomless metal or wood frames are usually three- to five-foot square with clear “roofs” made of glass, fiberglass or even plastic sheeting. The lids of cold frames can be hinged so that you can prop them open to allow air inside.
Benefits of cold frames
Cold frames extend the early and late growing seasons. In the fall, cold frames give your tender plants a few more weeks of productivity by keeping them warm longer when chilly weather would normally spell the end of the growing season. In early spring, when temperatures can still drop suddenly below freezing, a cold frame allows you to get seedlings off to an earlier start. Cold frames can also prevent foraging varmints from raiding your veggies.
Cold frames can even be used midsummer as long as you remember to open the tops for air.
Building a cold frame
You can buy a cold frame, but building one is an excellent DIY project. Cold frames can be made of lumber, but brick or concrete blocks will also work. If you can find one, you can use an old window or glass shower door as a lid. In that case, size the frame to fit the lid’s dimensions. You can also make the lid with a glass sheet or plastic sheeting.
Build your cold frame with the window lid sloped toward the sun’s prevailing direction so your plants will absorb the optimal amount of sunlight during the day.
Add a little warmth
Get a double benefit of nourishment and warmth for your plantings by using them to create hotbeds. Excavate around the plants under the frames and mixing compost or manure into the soil. As the material decomposes, it generates heat to keep the plantings warm and also provides nutrients.