The idea is to provide a greenhouse-like atmosphere for seeds and small plants in order to get an early start on the season or to extend the fall garden as long as possible. Cloches are set out over individual plants or are made into tunnels for whole rows. They trap solar radiation and moisture evaporating from the soil and plants. The hotcap is a simple form. There are a variety of forms on the market now, some work, some don't, and some are easily constructed from materials around the home.
Cloches are generally lightweight, portable, and reusable.
It is preferable to have a design that can be closed completely at night to prevent frost damage and opened or completely removed during the day for good air circulation. Cloches should be anchored or heavy enough that they don't blow away. Floating Row Covers Row covers are a more recent development in extending vegetable production past frost dates. As the plants grow taller, the plants push up the material. Row covers retain heat and protect against frost so crops can be planted earlier in the spring and harvested later in the fall.