A few weeks ago my friend Sally and I held a cold frame workshop at The Woodlands Community Garden. Sally is a community gardening guru, the person who runs the Garden Tenders program at the Pennsylvania Horticultural Society that I love so much.
A cold frame is like a mini greenhouse that you can use to cover a small part of your garden or place in the grass to start seedlings in. It warms the air and soil underneath it so you can grow crops even in the snow! Of course, you are limited by the height of the cold frame.
I'm using mine to cover the carrot seedlings I have in my plot with the hopes that I can warm the soil enough to get them to a decent harvest-able size before too long. We used aluminum and glass windows that we picked up for free in the trash, and some recycled plastic wood for the sides. The window simply sits on the top of the frame in our design, but you can attach it with a hinge for a fancier version.