Now that the crocuses and daffodils are starting to push their way out of the ground, I’ve gotten antsy for spring planting time to come. Someday in the future, I hope to build my own little greenhouse to give me a head-start on the season, but right now my time and money budget isn’t up for that project. Instead, I decided to build what is essentially a mini-greenhouse; a cold frame.
Cold frames work by the same principles as greenhouses. Sunlight comes in through the clear glass and is absorbed by the soil and plants. This warms up the soil and other materials in the greenhouse, which then emit infrared radiation, which is felt by both us and plants as heat. The neat part is that although glass is transparent to visible light, it’s not transparent to infrared radiation, so the infrared radiation is trapped inside the greenhouse and helps keep the plants and soil warm. The walls and ceiling of the greenhouse also protect the plants from the cold winds outside.
There are plenty of cold frame kits available, but I decided to go even cheaper and bought an old window in its frame from the Seattle ReStore. I gave this a few upgrades, like a new coat of paint and a sturdy handle for opening the window. I chose white paint for the inside of the frame, to reflect the sunlight and make it nice and bright inside. I painted the outside with black paint, in the hope that it will help the frame stay warm by absorbing any surrounding light. Also, those were the colors of exterior paint I already had around the house. I’m still not sure about the soundness of my color choices, since black on the inside would also have the advantage of absorbing sunlight and radiating it as heat.
I also bought a thermometer to keep track of the temperature inside the cold frame. If you’re tempted to make your own cold frame, learn from my mistakes; don’t get a thermometer that attaches with a suction cup to the window. It will fall down on your plants. On that note, does anyone have a recommendation for a small, sturdy outdoor thermometer?