Making the most of a short growing season

There are several ways to compensate for a short growing season, or to grow vegetables for extended periods, regardless of climate. Utilizing glass or plastic for protection can help you get the most out of your plants.

Greenhouses are designed to protect large numbers of plants, but the principle of using glass to protect tender plants from external temperatures can be applied on a small scale in the backyard vegetable or herb garden.

• An old window, for example, can be used as a mini-greenhouse, covering a container of seedlings early in the season to protect them from late winter or early spring frosts. Known as a cold frame, this technique is very effective because the plants get plenty of light and warmth from the sun, which encourages them to grow rapidly at the start of the season. As the weather becomes warmer they must be hardened off, which means that they are gradually introduced to external growing conditions by removing the cold frame (or propping or lifting the protective glass) for several hours a day. After two weeks of increasing exposure to the outside world, young plants should be ready to grow without further protection.
• Sheets of clear plastic can be used in the same way as glass to protect plants from the cold. Simply stretch the plastic sheeting over a frame or some small stakes so that it is about 30 centimetres (12 inches) above the soil level. Vegetable or herb seeds can be grown directly in the ground underneath the sheeting, or else small pots or trays of young seedlings can be placed beneath the plastic sheeting for protection. They can then be hardened off gradually and transplanted into their final position when the risk of any late frost has passed.
• Individual plants can also be protected by using glass. Young tomato plants, for example, can be sown early and have inverted glass jars placed over them at night or on particularly cold days. This technique can provide protection from frost, which will cause the plants to brown off and die overnight. Use the largest jars that you have, so that the stems and leaves do not come into direct contact with the sides of the jar — the cold night air will make the glass quite cold, and direct contact with this may cause the foliage to burn. In traditional European gardens, inverted terracotta pots were placed over tender vegetables in the evenings.