Ventilation of cloches
When cloches are used in rows, it is generally necessary to provide ventilation in warm weather—it is more important to ensure that you do this in hot, moist weather (or hot weather following rain) than during hot, dry weather, because a humid atmosphere under the cloches can all too easily encourage the build-up of pests such as greenflies and diseases such as botrytis (grey mould). This is more of a problem with plastic cloches.
Some types of cloches have special provision for ventilation; they may have handles or panels to allow one side of the roof to be opened in several stages. Most glass cloches can be ventilated by slipping the outside top glass into the notch on the handle. Otherwise, cloches can be ventilated by leaving a slight gap of about 2.5 cm (1”) between each cloche and its neighbour. Do not forget, however, that the ends of the row must always be sealed, with a sheet of glass or plastic, or even a piece of wood, otherwise the wind will rush down the tunnel, ruining your crops, and birds will be able to enter. Some firms make special end pieces for use with their cloches.
When using cloches to grow melons, which must be protected throughout the summer, be sure to give ample ventilation when the flowers open, so that bees and other insects can enter to fertilize the flowers.