A Cold Frame is an Economical Alternative to a Greenhouse

If you don't have money to burn, buiding or buying a cold frame is an economical alternative to a greenhouse. These garden structures, small in size and low to the ground are simply constructed, generally made with an aluminum frame and snap glass polypropylene panels for glazing. You can build your own frame enclosure using wood, glass or plastic. (Cold frame plans are also available online) If you build your own, or buy, keep these considerations in mind:

Must have good light transmission
Effective insulation
Enough space and depth to accommodate the plants you want to be housed

Cold frame uses

There are several important uses that a garden frame provides:

If you have tender plants that need protection, a frame is a good choice
You can use the enclosure much as you would if you had a greenhouse or nursery
Cold frames can provide storage if the greenhouse is full and a few extra plants need a home.
Force fruit and vegetables to crop out of season
Use the frame to harden off tender young seedlings or plants

Also see; hobby greenhouses