Protecting fruit from frost
First, let us consider strawberries, which are a rather special case as they are one of the few fruits small enough to be protected by cloches. In practice, cloches and polythene tunnels are mostly used as a means of securing an earlier crop rather than merely to reduce the risk of frost damaging the blossom.
Where cloches and tunnels are kept closed at night because of the frost risk, it is important to open them during the day whenever the temperature is above freezing, to allow pollinating insects to enter. Failure to do this will result in poor setting and malformed fruit.
Cloches and tunnels should be placed over the rows, preferably of first-year plants, during late winter. You will gain nothing by putting them on earlier than this.
To prevent strawberries becoming soiled in rainy weather, it is necessary to prop up the fruit trusses on wire supports or to cover thearound them with special strawberry mats, with a sheet of black plastic or a layer of straw. If you use straw, make sure you do not put it down too early or you will be inviting frost damage. Being light in colour, straw reflects heat rather than absorbing it and thus the air immediately above a strawed plot is likely to be a degree or two colder than over unprotected soil. Delay strawing until the fruit has set and the berries begin to weigh the trusses down.
If you are growing strawberries outdoors without cloche or tunnel protection, you can give them some measure of security on cold nights in late spring by laying sheets of newspaper over the rows; hold these in place with an occasional skewer made from a bamboo cane or a stick.
Perpetual-fruiting (remontant) straw-berries are usually untroubled by spring frosts and should their first flowers be blackened, their succeeding crops will be heavier. As a rule, the season of this type of strawberry ends with the coming of the first frosts of autumn. You can, however, prolong the picking season by a few weeks if you have the forethought to cover the rows with cloches in early autumn.
The covering of individual fruit trees in flower on evenings when frost threatens is not very easy, owing to their size, but in the case of wall-trained trees, the attempt is well worth making, and may mean the difference between a crop of apricots, peaches, nectarines, plums or pears and none at all.
Pieces of hessian, muslin or plastic sheeting may be used to protect fruit trees. Old curtains, tablecloths or sheets will act as good substitutes. Even the lightest of coverings, such as nylon netting or the wire netting of a fruit cage, can often avert disaster during a late spring frost; but in the case of severe frosts, nothing short of complete cover, such as hessian or polythene sheeting, over the trees will prove effective. The covering material should extend fully over the crop with the sides left open. Whatever type of cover you use, it should be removed first thing in the morning following the frost.
Soft fruits, such as gooseberries and red currants, trained against walls are as easy to protect as wall-trained tree fruits. All soft fruits grown as bushes— currants, gooseberries and blueberries— you can protect temporarily by throwing a piece of hessian, muslin or other suitable material over each bush. Again, remove covers in early morning.
Where figs are attempted in any but the warmest and most frost-free districts, some protection should be given in winter to safeguard the embryo figs which begin to form late one year to ripen the next. One method is to tie loose bundles of straw or hay over the shoot tips; with a tree trained against a wall, you can lean leafy branches (such as spruce branches) against it and then fill in the spaces with more branches intertwined horizontally.