|I would like to build a cold frame this year. My main concern is overheating. I am very afraid it will warm up to a high temp during the day. How warm does the outside air have to be with direct sunlight before the inside air can harm the young veggies?|
|It's the inside temperature that you need to be concerned with, not the outside temperature. If it begins to steam up, it's getting too hot. Use a thermometer to keep track of the inside temperature--with a maximum temperature of about 70F. But be aware that even on cool, sunny days the roof needs to be propped up a bit for air circulation. Steam and heat can really stress little seedlings, so keep an eye on them. With a cold frame, the ground is still quite cold and tends to moderate the temperatures inside. Also, on the threat of cold nights, it would be good to cover the closed frame with hay or thick blankets.
If you are not around during the day to monitor the temperature inside your cold frame, you can purchase automatic ventsthat will open when the inside temp gets too high, and close when it cools. Charley's Greenhouse Supply (ph# 800-322-4707) sells one that is opened and closed by a temperature-sensitive spring mechanism.