In referring to the common errors in the culture of shrubs and trees (see Chapter 7.) it was said that neglect of pruning accounted for many comparative failures. It was pointed out that different shrubs have different habits of growth, and that to get the best results these variations should be studied.
The true lover of shrubs and trees will never grudge the time necessary to learn their habits of growth and method of flowering. On the contrary, he will find interest and enjoyment in acquiring knowledge about them. He will see that some deciduous shrubs bloom best on entirely new wood, some on wood a year old, others on wood two years old or more.
We need look no farther than the Rose for classes typical of those kinds which do not produce their best flowers in spring, on shoots of the previous year, or on old wood, but on absolutely new shoots of the current year. With these the course is to prune the flowered shoots back to near the base, not absolutely to the old wood, but to within a few inches of it, leaving three or four buds (more or less according to the variety), from which the new flowering wood will start. It is usual to do this just as growth begins in spring. In such shrubs the old wood forms, as it were, a framework, a support, for the flowering wood. The old wood cannot be dispensed with altogether, as it can in the case of those shrubs which, like the Raspberry and a host of others, throw up shoots direct from the root stock. To avoid misunderstanding, it should be pointed out that although the Hybrid Perpetual, Tea-scented, Hybrid Tea and most other Roses have the habit indicated, the Ramblers and Wichuraianas have the Raspberry habit.
There are a few shrubs, of which the Rhododendron and the Camellia are popular examples, which produce shoots from the base of the flower trusses. Examine a Rhododendron in bloom and it will probably be found that growth buds are present at the base of the truss. This offers two practical hints to the cultivator: the first, that he should not cut Rhododendron blooms with long pieces of the supporting branch if he wants subsequent growth; the second, that after the bloom truss has faded on the plant it should be pinched off carefully with finger and thumb, so that the nestling buds may be left uninjured. These points are often neglected, with injury to the plant. When Rhododendrons are grown thinly they rarely need much treatment with the knife, as they develop a neat habit naturally and gradually extend their flowering wood. Should they get very crowded branches may be cut right out. When they get crowded, however, they may grow tall and lank, and so become unsightly. In such cases it is wise to attack them with a saw and prune them low. If they are happy in the soil they will break freely from old wood, and soon be compact bushes again.
We chose the dwarf hybrid classes of Rose as typical of the shrubs which bloom best on entirely new wood. Clematis Jackmanii might be quoted as another well known example.
The second group, that which flowers best on wood made the previous season, is a large one. The Rubus genus, of which the garden Raspberry is a familiar member, the Mock Orange, the Deutzia, the Rambler Roses and the Weigela are popular examples.
With respect to the third group, which bloom mainly on mature wood two years or more old, little annual pruning is needed, certainly there is no general cutting back as in the two other groups.
We might, indeed, form a fourth group: those which, in practice, need no annual pruning; they only require to be thinned now and then when the heads get thick.
Inasmuch as this diversity of habit exists among shrubs it follows that the same system of pruning cannot be right for all kinds, but if the grower fixes in his mind that nearly all the principal deciduous shrubs fall naturally into groups, and classifies his own plants accordingly, he will succeed. There are exceptions. Some shrubs, notably the Clematis, have no common habit throughout the species, and consequently these genera require special study; but they are not numerous.
We might usefully consider the groups one by one:
(1) The New-Wood Group. - In this section the annual pruning consists in cutting back the flowered growths of the previous year. It is not usual to cut them out entirely, but to reduce them to a few buds, because growth starts better from buds near the old wood than from the old wood itself. Pruning may be done when growth starts in spring.
(2) The One-year Wood Group. - Here the annual pruning consists in removing the wood which has flowered, and it may be cut out the same summer, because the new wood gets full exposure to sun through the thinning of the bush, and, becoming well ripened, flowers well the following year. Certain variations will be found within this group. Some of the shrubs will throw up most of their annual growth from the rootstock itself, like a Raspberry or a Dorothy Perkins Rose. Others will produce it on the upper part of the old wood. With the former, the annual pruning of the flowered wood will be to the ground level; with the latter, to the old wood from which it breaks.
(3) The Old-Wood Group. - The annual pruning consists in cutting back the annual growth close to the old wood. It is often spoken of as spurring. It may be done in winter or when growth starts in spring.
A strong, sharp pruning knife will be found the most useful tool for pruning deciduous shrubs, but secateurs may be used on occasion with groups 1 and 3. A small saw will be needed on occasion.
The grower soon learns by observation the difference between new, one-year-old, and older wood. New wood is comparatively thin, flexible and green, or greenish-brown, in colour. One-year-old wood is brown and firm, but the bark is smooth and clear. Old wood is dark and the bark is rough and dull.
Fig. The Persian Lilac. Photo by F. Mason Good.