Grow Grow: Build a Cold Frame

Our finished coldframe

There is lots of great info out there on building a great cold frame. The basics are...

southern exposure is good
a sheltered, warm spot like a south facing wall is a good site
an angled top makes the most of low winter/late fall/early spring sun. 45 degrees is good.
have in place a way to vent the frame and hold the lid all the way open so there is no cooking of plants.

Our version is made out of scrap wood with a polycarbonate panel I got at our local reuse center. It has a 45 degree angled top and is sited against a south facing wall. We rigged a bungee to hold the lid securely open against the wall. At night or during cold or stormy weather, the lid can be closed or propped partially open.

Scrap plywood becomes the box

The back is covered with stretched plastic sheeting

Cold frames are great because they do offer a few degrees of temperature protection, but I think one of their great features is they protect tender seedlings from wind. Seedlings need a bit of wind blowing through their hair to make them sturdy and strong, but they need small doeses of that at first. If you have all your seedlings outside and a windstorm (or hailstorm!) strikes, you can put them safely in the cold frame.

Moderating temperature inside is very important. If it is sunny, the lid should be open! I moved my hardy seedlings outside, when it was 36 degrees and sunny, and rapidly warming up. It could have been 36 and windy and cloudy and then I would have put them in the cold frame for protection. It is a balance between getting them sun, and protecting them from intense weather.