The gardener must at times give plants protection against too intense light and against excessively high temperatures.
Damage from intense light is most likely to occur when naturally shade loving plants are exposed to direct, strong sunshine; when sun loving plants, comparatively soft and tender from being grown in a greenhouse or cold frame, are transferred outdoors; and after plants are transplanted. The trunks of trees that have been growing closely together in woodland or nursery may be damaged by sunscald on their south facing sides following their transference to sunnier locations; by heavy pruning, branches previously shaded by foliage may be exposed to sunshine sufficiently strong to sunscald them. Damage by sun occurs not only in summer; in winter, when the ground is frozen, evergreens, especially, are likely to suffer from this.
The provision of shade is the obvious method of avoiding damage by light that is too intense. Shade needing plants should be grown in naturally shaded areas, such as woodland, under solitary trees or groups of trees, and areas shaded by high walls or buildings or in locations artificially shaded by lath houses, lath or burlap screens or other appropriate means.
The trunks of trees may, with advantage, be wrapped in burlap or in special tree wrapping
paper for a season or two following transplanting. When annuals, vegetables, young biennials and perennials are set out in hot sunny weather they should be shaded for a few days following the transplanting operation.
Not a great deal can be done to lower summer temperatures; but in every garden some locations are noticeably warmer than others. At the base of a south facing wall, for example, the temperature is very noticeably higher than at the base of a north facing wall; it is likely to be cooler near a pool or other body of water than elsewhere; parts of the garden that receive reflected heat from walls and pavements are warmer than those where plants grow alone in more open areas; in enclosed, “pocketed” spaces temperatures are higher than in more open locations through which breezes blow; and in the shade it is always much cooler than in the sun.
In selecting locations for plants known to prefer cool summer conditions, all these factors should be borne in mind. It should also be remembered that moisture has a cooling effect, and so plants should not be permitted to suffer from lack of water during dry weather.
As a temporary measure, shading may be used to offset some of the ill effects of temperatures that are too high. Spraying the foliage lightly with water lowers its temperature somewhat and has a refreshing effect on plants.
Many plants Clematis and Lilies, for example can withstand high atmospheric temperatures, provided the soil is kept reasonably cool and moist. In really hot weather an even temperature at the roots and a steady supply of water go far to ensure success with a great many kinds of plants, especially those that are surface rooters such as Azaleas, Blueberries and Rhododendrons. Summer mulching is an excellent garden practice designed to conserve moisture and keep the soil temperature moderate and even.