Master gardener: Control the temperature of the garden with a cold frame | Home & Garden
If you have an old window with the glass intact, these make great tops for cold frames. Alternatively, you can cover your lid with clear plastic. Since plastic can lose heat quickly, you can use two layers of plastic just to provide a little extra protection. The height of your cold frame should be enough to exceed the crop you want to grow. You can also put some weather stripping where the cover meets the frame to help keep the heat in. Windbreaks are also a great idea to help protect your cold sash from strong northerly winds. It can be as simple as a few bales of straw, but be careful not to shade the bed.
When you use a cold frame, you become the thermostat. If it heats up enough, you may need to open the lid to allow some cooler air to circulate around the plants. On colder days you may want to leave it closed. Either way, unless we’re having a heat wave, you’ll want to close the lid at night to help lock in the heat.
Water will be the key to your cold frame, and you should water in the morning as you would your regular garden. We water in the morning so that the water can evaporate from the leaves before dark. It helps to minimize disease in your garden.
Cold frames are not only great for helping you extend your fall growing season, but they can also help you start your garden earlier in the spring. With a cold frame, because the soil and air inside the cold frame are warmer, you can start your seeds or transplants outside before our last average frost day of April 15th. Once we have passed the danger of freezing, you can either open the lid or remove it permanently for the rest of the summer season. Happy gardening!