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Using a Cold Frame to extend the Growing Season

tomatoplantsTo get the most out of your garden you need to be able to shelter your plants from cold weather during the winter and early spring.

A cold frame is a relatively inexpensive and simple structure providing the ideal environment for sheltering plants and for growing cool-weather crops.

Cold frames do not require an outside energy source as they rely on the heat of sun making it economical as well as practical. If needed, some “hot” manure can be added beneath the compost to add some bottom heat.

To make the most of this heat source your cold frame should be located against a south facing wall or fence or the side of a shed or greenhouse. Position the cold frame on a slight slope to ensure good drainage and maximum exposure to the sun and site it in a sheltered spot with a wall or hedge to the north to protect from winter winds. If possible, sink the cold frame into the ground to provide protection and use the earth as additional insulation.

Building a Cold Frame

There are lots of plans available for building a cold frame. However, Gardeners Worlds’ Toby Buckland made one for the show which is ideal. Here’s what he says:

  1. Buy your window first and make the frame to fit. A salvage yard or reclamation yard is an ideal place to buy – we paid £15 for ours.

  2. Make the sides from 15cm wide planks (we used recycled floor boards) with 50mm (2? x 2?) timber batten in the corners for extra strength.

  3. The only tricky part is cutting the plank for the sloping sides a – job best done with an electric jigsaw. If you haven’t got one give the frame a flat top but be prepared to tip the water that will collect in the window lid away after rain regularly.

  4. Fix hinges between the back wall of the frame and the window lid. Give the inside a coat of White emulsion to increase light levels and plant growth.

  5. Position in a bright spot ideally with the lid angles towards the south to catch as much sun as possible.


Additional insulation my be necessary when frost is expected. The simplest way to do this is to fill burlap or hessian sacks with leaves and place on the top to protect against freezing. Another method is to stack straw or hay around the sides of the frame.


On sunny days it is vital to provide some ventilation. Just prop open the lid and don’t forget to close it again at sunset.

Using your Cold Frame

In early spring a cold frame is useful for hardening off seedlings which have been sown indoors or in a heated greenhouse. This hardening off ensures that seedlings are properly acclimatised before being planted out. The cold frame can also be used to get an early start with hardy and half-hardy annuals.

In summer the cold frame can be used to propagate root cuttings from a vast number of plants.

In autumn you could sow some cool-weather crops to keep you in greens and root vegetables throughout most of the winter months. These crops include beetroot, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, garlic, leeks, lettuces, onions, parsnips, peas, shallots, spinach, swedes and turnips.