During the winter months it is essential to protect seedlings, new plants or those susceptible to frost, from the cold. While it is perfectly acceptable to take them indoors, this is often impractical. There is another popular solution that is cost-effective, doesn’t take up too much space, and is extremely efficient at keeping plants warm when the temperature drops outside.
A cold frame is a simple structure that is built low to the ground, completely enclosed and has a transparent roof. The idea behind it is simple: to protect the plants inside from the elements, while allowing heat to enter and making it difficult for it to escape. They are called cold frames because, unlike a hotter or often heated greenhouse, they rely only on the temperature gained from admitting sunlight, so are somewhat colder than greenhouses.
The main reason that cold frames are so popular with gardeners is that they are easy to make at home and also cheap to construct, while being effective at keeping plants protected. Here’s our how-to guide for those looking to build a cold frame at home.
Step 1 – Location
Firstly, you must decide upon a suitable location for your cold frame. The first consideration must be the arc of the sun; the majority of cold frames are south facing to take full benefit of the winter sun. It’s also wise to have them sheltered from the wind as much as possible and, if you’re leaving the bottom open, water drainage must also be considered.
To meet all of these criteria, many people place their cold frame next to the wall of their house or along the edge of their garden fence or wall.
Step 2 – Size
The size of your cold frame will be dependent on the number of plants you intend to keep inside. Remember that you’ll need to provide enough space for your plants to be comfortable when inside. The majority of designs are higher at the top and slope down to a lower front edge, providing plenty of room for plants as well as making it easily accessible.
Decide on the width, depth and height of your cold frame so that you can buy the right amount of wood, as well as the right size transparent sheet to go on top.
Step 3 – Construct Your Frame
The frame can be constructed out of many materials, but wood is the most common choice. You won’t even have to go out and buy brand new wood; you could use scrap pieces you have in your garage, offcuts from a local business, or railway sleepers from a salvage yard.
Generally a cold frame is one or two foot tall, with a diagonal at the front for easy access, to capture more sunlight and to allow water run-off. If you are building your frame on solid ground, consider adding feet (about 1 or 2 inches high) to keep it off the ground.
Step 4 – Construct The Roof
To make the roof you’ll need a couple of extra bits of wood, a clear material to allow light to enter, and some heavy duty springs that are suitable for outdoor use. Almost any clear material can be used, but acrylic or polycarbonate sheeting is a good choice as it is lightweight and extremely strong, as well as allowing light and heat to enter.
Attach the roof to your frame with the hinges, making sure that it fits snuggly so that the winter elements can’t get to your plants.
Step 5 – Protect Your Plants
Once you’ve finished your cold frame, simply situate it in the right place and place your plants inside. You can either plant them directly in the soil (if your design has no base) or put them inside in their pots.
Remember to water them when necessary and, on a particularly warm day, you may need to prop the lid open for a short while to allow ventilation.