Cold Frame Gardening - Why You Should Love Cold Frames

When heated greenhouses came into existence, cold frames were usually located on the outer portion of the greenhouse and were made of a glazed glass covered frame that had a hinged roof also made from glass. This frame was unheated unlike the greenhouse and hence, it's name cold frame. It was used to harden seedlings which were initially grown in the greenhouse.

The hardening process involved keeping the seedlings and gradually opening the hinged roof more and more so that the seedling would acclimatize to the outside conditions. The hardening process ensured that seedlings did not suffer shock when planted outdoors and therefore, could grow unhindered.

However, in present day, the frames no longer use glass. Instead most of them are made from polycarbonate, which is as clear as glass and is double glazed to provide as much thermal insulation as glass.

Cold frames available today are either glazed down to the ground or they have a wooden frame. The wooden framed ones have the advantage of absorbing heat throughout the day and it is released gradually in the night. This means that the average temperature in a wooden frame would be higher. However, glazed cold frames are best suited for days when the sky is overcast as they can capture more heat from minimum of sunlight. So, both types have their pros and cons.

Even today the frames are used to harden seedlings. In addition, people also use them as mini greenhouses to germinate plants earlier than what they would if planted outdoors. Using a cold frame, you can harvest vegetables like cauliflower in late May. If you sow cauliflower seeds late October in the cold frame, the seedlings will be ready to be planted outdoors by end of February or beginning of March; and you will have fully grown cauliflower for your kitchen in late May. The idea behind a cold frame is to gain additional growing time. You can use a cold frame to grow other vegetables like onions, courgettes, sweet corn and lettuce.

Most people do not realize the value of a cold frame until they get one and then they wonder how they managed without one all this time. Remember, the money spent on getting and fixing a cold frame is worthwhile. Just the hardening of seedlings should be worth the expense.