The Cold Frame
an Easy Way to Extend the Season
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I use a cold frame to extend my very short growing season of 100 frost-free days. In fact, it stays so cool here, that I need to keep the tomatoes and peppers covered so they produce better.
These frames, or mini greenhouses can be as simple or complex as you want them to be. Plastic covering your plants propped up with water jugs and held down with rocks qualifies as a cold frame.
A word about plastic
The problem with plastic is that it blows away easily, and usually needs to be replaced every year. Water logging or snow logging can occur with this method. That is, water or snow pooling on top of the plastic and forcing it down on top of your plants.
The most economical plastic is the kind that can be bought in rolls, usually in the paint section of the hardware store. It’s usually called plastic sheeting and comes in 4 mil and 6 mil thicknesses.
Unless the plastic is UV resistant, you most likely need to replace it every year.
There is also a type of vinyl sheeting available. It is very thick and clear as glass. It is sold by the foot, and it costs a lot more than the plastic sheeting. The problem is, in temperatures below freezing, it splits. It can be used if you provide a hardware cloth backing so it will not move. Otherwise, I think you will be disappointed with your investment and results.
A step up from laying plastic on the ground and putting rocks on it is to build a hoop house. To build a hoop house you will need to attach 1/4 inch or 1/2 inch PVC to a bottom frame. There are some metal brackets available which allow you to do this easily.
Then cover with plastic and staple the plastic to the bottom frame. It’s best to wrap the plastic around the bottom of the wooden frame and staple on the inside. Or, you can staple the plastic on the outside and nail a wooden strip over the plastic to reinforce the connection.
The dimensions of the hoop house are up to you. You can make one that you would need to crawl into or lift off. Or you can go whole hog and make one you can walk into. That would be more of a greenhouse.
Check out the video for a step-by-step how to build a cold frame using the hoop house method:
Box type Another way to build a cold frame is to construct a box and cover the top with glass or plastic. Wood is a traditional material for a frame box. However, the box can be made from stacked up cinder blocks, bricks, or straw bales. Many people use discarded windows for the top of the box. Or, as I mentioned, it can be covered with plastic. It’s handy if the top is able to be propped open to prevent overheating. Build up the box as tall as you think you might need. If you are going to protect seedlings and then remove it, you may only need 6 inches. If you plant to allow pepper plants to stay all season, you might need 3 ft. You may be able to prop glass or plastic up with the edges of your raised bed, if the soil is beneath the level of the bed. Creating a slant for the top of the box helps gain maximum light and heat. Forty five degrees is an easy angle to aim for. This step is not absolutely necessary.
A brick cold frame courtesy of Mellochamp 75 on flickr
Cold-frame case photo courtesy of Dawn Olinek @ dawnolinek.com
Links to cold frame plans
pitched-roof with hinges