Choosing what time to prune
It is often said that winter pruning of trees is to promote growth and summer pruning to stimulate fruiting. Like most generalizations, this is not entirely true. The cutting back of a shoot in winter is likely to cause growth in spring, perhaps several new shoots where previously there was one, and the more we cut off a shoot, the greater will be its efforts to grow the next season. Therefore winter pruning stimulates growth, the harder the pruning, the greater the growth. The tree which is weakly should be pruned hard and the one which has been cropping freely should be pruned lightly.
Nevertheless, even in winter pruning you must think ahead to fruit bud development. In all pruning you are trying to achieve a balance between wood growth and fruit production in each individual tree, necessitating an adjustment to your procedure, season by season, to maintain that balance. Remember that if you cut a shoot, it will produce more growth, but if you leave it uncut buds will become blossom buds during the following summer to fruit the year after that.
Summer pruning, however, will not induce more growth but rather restrain it. Always avoid doing this too early in the summer, otherwise secondary growth takes place and in due course this, too, has to be dealt with; meanwhile there has been considerable wastage of the tree’s resources and energy.
Summer pruning is an essential part of the method of growing trained apple and pear trees. It may also be adopted with trees grown in the bush form if they are growing vigorously: it then improves fruit colour and quality by admitting more sunlight, and may aid fruit bud development. Never summer prune a bush tree which is behaving indifferently as this will only weaken growth still further and reduce an already poor crop.
If you are cutting back to limit size, prune when the blossom is open, for cutting at that time has the greatest growth-stopping effect. You would do this when, for example, a cordon has reached the top of its cane, or when a pyramid is as high as you wish or its branches are overlapping those of its neighbour.
Blackcurrants and all cane fruits except autumn raspberries can be pruned as soon as their crop has been picked. The other soft fruits are pruned in winter but those trained as cordons, espaliers or fans need pruning in both summer and winter. Gooseberries grown as bushes may be pruned in winter but often this is deferred until early spring, even until the young leaves are unfurling, so that bare, bud-pecked shoots can clearly be seen, and to ensure that when you do prune you cut to a living bud. This delay is not ideal from the growth point of view but preferable to losing much of your potential crop to birds.
Risk of disease is another important factor in the timing of pruning. The best-known example of this is the vulnerability of plums to silver leaf disease, one of the most serious infections with which the garden fruitgrower may have to contend. This is a fungus disease spread by spores entering open wounds—such as the cuts made by the pruner. From early autumn, through winter and into late spring, this infection can occur quite readily, most often within a week of the wound being made. During the summer months, however, the tree quickly produces a protective gum when the wood. Is cut and this renders infection unlikely.
Midsummer months, therefore, are the safest for pruning established plum trees and this may be done immediately after picking. Young trees, having their framework of branches built up should be pruned in the spring, as late as possible, just as growth is about to start and wounds will heal quickly. Even with that precaution it is advisable to seal all cuts immediately with a coat of bitumen tree paint, softwax or real white lead paint.
A similar precaution with timing can be taken where apple canker has been rife. In this case pruning is best done in mid- to late winter, when fewest canker spores are about.