In Mediterranean and other dry or semi arid regions, regular irrigation is an integral part of having a garden. Usually, the amount of water available to the home garden is severely restricted, but within known limits, the garden plants can nonetheless be grown satisfactorily.
In climates typified by long, hot, dry summers, the gardener is dependent on the amount of winter rainfall. In the Eastern Mediterranean for example, the average annual rain amounts to about 500mm, all of it falling between November and the end of March. Naturally, during dry winter years, it is often necessary to cut back on water use during the summer. The question arises therefore, as to how this should be done.
The most common reaction is to refrain from watering the ornamental landscape trees. The homeowner looks at the browned-off lawn, the wilting flowers, and at the same time, sees that the trees appear green and healthy. The reasonable conclusion is that the trees can get by without irrigation, while the other garden plants cannot. This approach, however logical, is mistaken and ought to be reversed, for no other garden element can even begin to match the precious value of a tree. In years of drought, it is preferable to give up on the lawn and flowers, rather than risk the health of the trees and shrubs.
To put the matter in perspective, the bottom limit required by the most drought-hardy trees is thought to be around 300mm per year. This would apply to such species as Tamarisk and Pistachio. Most landscape trees however are dependent at the very least, on the 400-500mm of rain that fall during an average winter. If there is a shortfall and especially if a number of drought years follow each other, the trees will suffer.
The crucial point to remember is that water stress usually inflicts irreversible damage on a tree BEFORE it starts to show obvious symptoms of such stress. The tree's hardiness to pests and disease for instance, is very much a function of this. The wise gardener therefore, accepts as axiomatic, that the first signs of distress in the tree (i.e. sudden leaf drop, or dead branches) are invariably the beginning of the end for that specimen.
Fruit trees, with exception of such species as Olive or Carob, require extra water in order to produce quality fruit. In drought years, it is possible to reduce the amount of water, by irrigating them on the same regime as the water-conserving trees. The fruit will be adversely affected of course, but you can save the tree as a whole.
While trees can live from anything between 30 and hundreds of years, shrubs and bushes have a garden life span of some 20-30 years. They therefore constitute the second most important plant element in the garden, at least as far as stability is concerned.
For our purpose here, shrubs can be divided into two broad groups. The leaves of those whose foliage is soft, tend to wilt when there is a lack of moisture. There is nothing to worry about here. When that happens, a slow, deep watering will cause them to recover, without the plant incurring significant damage. Three or four of these waterings are often sufficient through the year.
The other group concerns those bushes whose leaves are hard and leathery, such as Carissa or Star Jasmine. This property is an archetypal water-conserving devise, but it is here that gardeners are liable to make a serious mistake. As with most trees, shrubs of this kind can survive successive years of drought without displaying outward symptoms of stress, but when these do appear, it is often too late, and the plant is firmly set on a downward course to decline and an early death. Therefore during drought years, water such plants with the rest of the shrubs and bushes in the garden.
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