A cold frame is much smaller than a greenhouse but functions in much the same way by letting light in whilst protecting your fragile plants from the cold. It traps both heat and humidity which creates an ideal environment for plants to prosper. They are easy to build and can vary greatly in size and material depending on your preferences.
The sides of the cold frame can be made from untreated hardwood, bricks or pavers and a window or glass shower door can be used for the roof. When hinging the window to the frame make sure to angle it towards sun to maximise its effect. The correct position for a cold frame is north facing preferably in a place protected from the wind which receives as much sun as possible. This way, your cold frame will catch most of the sunlight which in turn will warm your little plants.
In order to keep the lid up when working and also to allow ventilation on warmer days, make sure to include lid supports. Adding both short and long lid supports will allow you to decide the size of the gap allowing more or less ventilation depending on weather conditions and the needs of your plants.
After you have finished building your cold frame you are ready to sow as you normally would in the garden. Strawberries and salads work really well in a cold frame so why not give it a try and enjoy the extended growing season!