Pre-warming the soil in spring can help crops to germinate earlier than usual, increasing the length of the cropping season (3-4 weeks at either end), and making maximum use of available ground. For example, a cloche can raise the local soil temperature by up to 10°C and hasten germination of direct-sown crops by 10-14 days. This, in turn, raises air temperatures and also reduces the amount of heat lost at night, resulting in earlier harvest dates (3-4 weeks with most crops).
Ideally, cloches and other soil warming measures should be in place at least one week before any crops are transplanted or sown into the soil, to allow temperatures underneath to rise sufficiently. Temperatures near the surface will tend to fluctuate but lower soil levels will retain some of the accumulated warmth. Glass cloches are especially effective as they retain more warmth at night.
Wind protection increases growth rates and leaf surface area, and also promotes ‘softer’ growth. This is useful for leafy crops such as salads, spinach and cabbage where soft growth is desirable. If exposing such crops it is essential to harden them off as lush plants quickly wilt if suddenly exposed to strong wind or sunshine. To do this lift the lids and sides of plastic and fleece cloches to increase ventilation for a week or so before exposing fully, and remove rigid plastic or glass cloches for a few hours each morning a week before full exposure.
Cloches keep off hail that can damage young plants and deflect heavy rain that can damage soil structure, seedbeds, young plants and contaminate produce with splashed soil.
Pest and disease protection
Used as a physical barrier, cloches can be a useful way of protecting crops from specific pests or diseases. Cloches are less effective than fleece or insect proof mesh at excluding pests but will prevent bird damage.
Well-ventilated cloches can reduce common air-borne diseases such as onion downy mildew and tomato blight by reducing wetting by rain. Foliar diseases need adequate moisture on the crop foliage to infect so keeping leaves dry is a good preventative measure; just aim to reduce humidity through good ventilation too (e.g. opening any air vents, or lifting up a side of the cloche).
Over-wintering and ripening crops at the end of the season
Cloches offer frost and rain protection of autumn-sown crops such as carrots and chicory. They 'buffer' temperature for late-ripening crops such as bush tomatoes and chillies too, reducing the sharpness of early frosts.
Cloches covered with black polythene can be used to blanch endive and chicory, where the bitterness of these leafy salads is diminished and succulence increased by excluding light for several weeks.
Black plastic clad cloches can also be stuffed with straw or other insulating material and placed over root crops to keep them sound and accessible in freezing winter weather.