Extend your harvest with a coldframe for warm plants

September 18, 4:44 PMGardening ExaminerRobin Ripley

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A coldframe will protect your plants from the cold
and extend your growing season. You can buy
excellent coldframes like this one online, but it's also
easy to make your own.

It's getting chilly here in the Mid-Atlantic and many of my gardening buddies across the country are already facing nighttime frosts. But it's not the end of the growing season if you have a coldframe that can keep your plants warm. This year I'm growing lettuce, spinach and even trying some parsley in my coldframe.

A coldframe is an enclosed structure placed right on the earth to create a mini greenhouse-like environment. It only needs to be wide enough and tall enough for the plants to grow and for you to work inside. Alternatively, you can create a hinged or removable top so that you can access the plants inside. Any coldframe will need to have some sort of ventilation to control moisture and allow in air on warmer days.

There are many mail order kits available, such as the one pictured from MasterGardening.com. But inexpensive coldframes can be easily constructed with a minimum of skill and just a few tools.

Coldframes can be made from salvaged materials, such as old storm windows or window frames. If you use salvaged materials though, make sure the frame hasn't been painted with a lead-based paint--a common paint ingredient until about 30 years ago. (If you're not sure, look for do-it-yourself lead test kits on the Internet.)

Most of us don't have access to salvaged materials, so constructing a coldframe from materials easily found at the hardware store is the best solution. One coldframe that is functional and easily assembled with a saw, scissors and wire nippers can be made with 2" x 4" boards, concrete reinforcing wire and plastic. P. Allen Smith shows how on this handy video. 

Unlike Smith's coldframe, mine has removeable ends to the tunnel to keep in more heat as winter sets in. A minimum/maximum thermometer is also a handy addition to help you keep track of the temperatures inside your coldframe.