I have a metal frame left standing on my south deck which is 10′ X 10′. If I wrapped and covered this with thick plastic sheeting, would it keep my plants alive through the winter? Thank you, Cecile.
Answer: Well, this will help protect some plants during your winter season, but you will need to know the plants’ Hardiness Zone. Your location is Zone 8a. Typically, adding one layer of protection, like a heavy plastic sheeting or row cover fabric, will add one Zone in protection, so theoretically inside would be Zone 9, and you can add an additional cover or protection inside for an additional Zone. You begin to get a significantly diminished light source with the second layer, so be selective on what plants you are protecting. Make sure that the plastic and structure are securely fastened down, as this will be highly susceptible to high winds and could easily blow apart, exposing the plants to weather they are unaccustomed to. A UL-approved heater for wet locations could also be added. Just make sure it’s in a properly grounded outlet. I’ve also used a remote thermometer so I can keep track of night temps in my temporary greenhouse, and you want to make sure that there is a way to vent it on sunny days, as the temps can climb rapidly.
Do some reading on greenhouses and cold frames to see how they are best secured to a structure. Also make sure to research the Zone of the plants you are trying to overwinter to see what they like. Some tropicals can be put into dormancy and overwintered in a basement or garage that stays above 45 degrees, much easier than worrying about them outside!
Good luck with your cold frame.