Cold frames are a vital component in the gardener’s toolkit. Use them to start off seedlings earlier in spring, to carry on cropping vegetables well into winter, or to help harden off tender plants such as chillies in early summer. They really are the gardener’s best friend! If you don’t want to splash out lots of money buying one, don’t – read on or watch our video to discover just how easy it is to make your own.
Homemade Cold Frames
A cold frame is simply a box frame with a clear lid (also known as a ‘light’) on top. The frame is normally constructed from wood but other materials such as blocks or bricks are also common. The clear lid lets in the sunlight, trapping warm air inside while protecting plants from inclement weather.
Because of its uncomplicated structure, a wooden cold frame makes an excellent DIY project. Salvaged windows will give you an instant lid, with the frame measured and cut to fit. Slope the lid towards the midday sun for maximum light and warmth. Position your cold frame directly onto the soil or on concrete or slabs.
Materials and Tools
To make a cold frame start with an old, salvaged window or windows or a clear door, such as a shower door. If you can’t get one, use a sheet of glass or twinwall polycarbonate secured to a simple wooden frame. To fix the lid to the frame you will need some strong hinges, and if you wish you can also add handles.
To make the box that the lid sits on, cut lengths of pressure treated lumber to match the dimensions of your lid (or lids). Make sure the back of the cold frame is one board higher than the front to give a slope that will shed rainwater and maximise the amount of sunlight available to the plants inside.
In our project, we’re using three boards at the front and four at the back. Seven shorter boards make up the sides. The seventh length is cut in half diagonally to give two identical triangular boards – one for each side, to match the slope.
All of the boards will need screwed to four vertical corner posts which match the height of the front and back boards. You will also need two battens of different lengths, which will enable you to prop open the lid on sunny days.
To put the frame together you will need some wood screws, a drill and a screwdriver.
How to Make a Cold Frame
Begin by screwing the side boards to their corner posts, using two screws at both ends of each board. You will find it easier to drill pilot holes before screwing the boards into place. You will need to screw the narrow end of the triangular top board at each side vertically down into the board below.
Now screw the front and back boards to their corner posts in exactly the same way.
The completed frame is now ready for the lid or lids. Carefully position the lid onto the frame so it is flush with the frame at the back, and screw on your hinges. Longer lids may need several hinges along their length.
The only thing left is to screw the lid supports into place. Position these on the inside of the frame, a short one on the front, and a longer one on the side. They should be just loose enough to swivel up, enabling the lid to be propped open at different heights to allow more or less air in.
You can also screw some handles on the lid to make it easier to open. And there you have it – your cold frame is ready to use!
Using a Cold Frame
Cold frames can be used to grow hardy salads throughout winter, or to get a head start on the growing season. For example, strawberries grown in a cold frame will be ready to pick a whole two weeks ahead of those grown outside, or you can use it to start off tender crops such as squash. You can also use your frame as a halfway house between your house or greenhouse and the garden to harden off plants before they’re planted out.
You can find cold frames to help plan your growing season in our Garden Planner. Select ‘Structures’ from the selection bar drop-down menu, then scroll through to choose a cold frame. Drop the cold frame over your crops, using the handles to adjust the exact orientation and size of the cold frame. Then click on the Plant List to see the effect this has had – often crops planted in a cold frame can be sown, planted out and harvested a full half month ahead of those grown solely outside, while the harvest period can be extended by a similar length of time.
Make a cold frame and you’ll enjoy a longer growing season, which as a gardener is certainly great news! If you have a homemade cold frame why not share your tips for building one by dropping us a comment below.