Guides to building a Cold Frame to extend your growing season

A Cold Frame is a simple structure which looks like a small greenhouse. It is used to extend a growing season by creating a warm, enclosed space to protect plants from frost and low temperatures. Cold Frames can take many different formats and can be as simple or as complicated as you want. On April 30th 2009, with funding from DoSomething.org, the Global Education Association led a work day building cold frames as part of its Groundworks program.

The following are some resources if you would like to build your own cold frame.

• “ToolGirl” Mag Ruffman’s guide. This cold frame uses an old window and includes a “floor” which can be left out. Skill level: Medium
• Canadian Gardening’s guide. This plan includes “boosters” to accommodate taller plants and includes tips for specific plants. Skill level: Medium/Low
• Gardenfork.tv’s guide (video). This is a simple PVC pipe/plastic sheet cold frame. Great if you can’t find an old window. Skill level: Medium/Low
• Joe Gardener’s extremely simple cold frame (3 minute video). This uses hay bales for the sides for a very quick, very inexpensive solution. Skill level: Low

General tips: A cold frame can be extremely simple or very complex but it is basically 4 pieces of wood with glass, plexiglass or plastic sheeting over the top to keep heat in. If you angle the top and face it south, it will get more sunlight and heat and extend your growing season even longer. In the summer, make sure you take the lid off during the day otherwise you will cook your vegetables right in the garden.

The GEA Groundworks work day:

Much of the materials for this project were cut but Tulipwood and were sponsored by Helping Nature Heal and by the Global Education Association through a Green Grant from DoSomething.org.

The first step was to build the lids from plexiglass and 1×3 boards. Holes were pre-drilled into the plexiglass so it didn’t crack, then it was screwed onto the wood frame. The plexi glass is 1mm smaller than the wood frame all the way around to keep any sharp edges from cutting anyone.

The exact size of your cold frame does not matter. It can be 4 feet by 8 feet, 2 meters by 2 meters, half a furlong by 50 spans - it really makes little difference as long as it all fits together. Just make sure the frames and lids are “squared off” or it’s going to be a very odd shape!

While the lids were being built, others were assembling the frames. These are simple 2×6 treated planks cut to the right size and screwed together.  There are 2 levels to this box, the bottom level is completely square, the top level has a slight downward slope cut into it to catch the sun (face the lower side to the south to get more sun).

Around the inside of the bottom later there are several small 1×2 “tabs” screwed on. These stick above the rim of the bottom later and the top layer justs slots in on top of them, holding it in place.

Once the frames were built, they needed to be filled with dirt. Everyone helped move a lot of dirt.

Right as the sun was going down, we put the finishing touches on the cold frames - 1×2 “tabs” around the outside of the top frame to hold the lids in place. The lids are not attached so they are easy to lift off completely on hot days.