Vegetable seeds can be sown in cold frames to extend the season and get earlier planting.

Cold frames are used for:

• extending the gardening season by several weeks in both spring and autumn, by protecting tender plants from cold, windy weather
• propagation
• hardening off
• winter protection of plants

What is a cold frame?

A cold frame:

• is an unheated bottomless box
• has a hinged or removable clear lid, usually glass
• is similar to an unheated greenhouse
• protects plants from rain, wind and cold temperatures
• provides a small amount of insulation from temperature fluctuations
• allows adjustment of ventilation by opening the lid to varying degrees

How a Cold Frame Works:

• the sun’s heat is absorbed through the clear lid during the day
• the soil inside the box heats up & provides warmth at night to protect plants
• the suns energy can be stored in ‘night storage’ units such as litre cola bottles, painted black and filled with water, which absorb heat during the day and release it at night.
  This will keep the temperature more even & prevent drastic drops in temperature at night.

Summer vegetable plants may be started in a cold frame, several weeks before outdoor planting:

• plants grow faster, because the temperature is warmer inside the frame.
• the frame can be lifted off the plants when the weather has warmed up, so that they continue growing in the same place, or the young plants can be transplanted.

Vegetable gardeners can build a cold frame from untreated wood and UV-resistant, greenhouse poly sheeting. Alternatively, cold frame kits are available from mail order or garden centres.

This picture is of a cold frame made of oak:

Wooden ones are more expensive to buy than metal cold frames:

Alternatively, bell boys work well for individual plants like courgettes.

Sowing vegetable seeds in a cold frame allows them to be planted a few weeks early.