Shrubs: Dead-Heading and Pruning Tips
SHRUBS FLOWERING ON WOOD PRODUCED IN CURRENT YEAR
These include caryopteris, buddleias, some escallonias, the hardy, Hydrangea paniculata grandiflora, some hypericums, Indigofera gerardiana, Leycesteria formosa, the golden elders, certain spiraeas, and Tamarix pentandra.
In mild districtscan be carried out at any time during the winter, but in exposed districts, or where there are frequent spring frosts that may damage the young growths, it is best not to prune until April.
Some plants, such as caryopteris, may be cut down each year to within a few inches of the ground, but others if treated in the same way will not grow very large. If a large specimen is wanted, build up a framework of stem and main branches by pruning the old growths to within a few inches of their base. This forces them to produce new growths from the buds that are left, and these in turn are cut back the following year to within a few inches of their base.
If the bush eventually grows too large, prune it more severely to keep it within bounds.
Other plants, such as certain cornus (dogwoods) and salix (willows), which are grown for their winter stem colour, must be cut down to the ground in late spring to induce them to produce new, brightly coloured shoots.
SHRUBS FLOWERING ON WOOD FRODUCED IN PREVIOUS YEAR
These include weigelas (diervillas), some forsythias, Jasmimim nudiflorum (winter jasmine), kerrias, some spiraeas, and philadelphus.
Cut away the shoots or branches that have flowered as soon as possible after thehave faded in order to give the new shoots an opportunity to develop properly and to ripen in late summer.
SHRUBS THAT NEED NO PRUNING
Among the shrubs that can safely be left unpruned for many years are amelanchiers, aucubas, arbutus, azaleas, bamboos, most berberis, camellias, ceanothus, choisyas, cistus, clerodendrums, coluteas, cornus (except those grown for their stems), cotoneasters, cytisus, daphnes, eucryphias, gaultherias,, , , hydrangeas (except H. particulate grandiflora), Jasminum officinale, lavandulas, hipinus arboreus, magnolias, myrtus, paeonies, potentillas, pyracanthas, rhododendrons, , ribes, rosmarinus, Senecio laxifolius, syringas, viburnums and zenobias.
These shrubs need no pruning unless they grow too large for the space allotted to them, when it is best to remove whole branches right back to their point of origin in the winter. Do not chop off bits of branches because this results in the rapid production of new shoots.
If frost kills or damages some growths, cut them back until sound wood is found. Do this in May after the frost is over.
SHRUBS THAT NEED DEAD-HEADING
The shrubs that benefit from the removal of dead flowerheads include azaleas, cytisus, kalmias, Lupinus arboreus (tree lupin), rhododendrons, Senecio laxifolius, syringas (lilac), and zenobias.
Remove the dead heads soon after the flowers have faded so that new growths can develop properly.
GENERAL NOTES ON PRUNING
1. Always use sharp tools. The professional gardener often uses a very sharp knife, as he considers this is less likely to damage the wood than secateurs, but in the hands of an unskilled person a knife can be dangerous when used for pruning, and a good pair of secateurs, kept sharp and used properly, is nearly as effective.
A common fault is to damage the branch while trying to cut through wood that is too thick for the tool. Secateurs should not be used for branches more than 1/2 in. thick. For these a pruning saw, curved or straight, is preferable.
2. Before sawing through a thick branch, make a saw-cut on the underside, a little distance from the point at which the branch is to be removed. Then saw through from above. By doing this the branch can be prevented from tearing the bark when it falls off.
In any case, when sawing off large branches, it is always better to repeat this operation at intervals along the branch to avoid damage.
3. After sawing off any branch more than ½ in. thick, pare the edges of the cut neatly with a very sharp knife. Then paint the wound over with a proprietary preparation such as Arbrex, white lead paint or Stockholm tar to prevent the entry of disease.
4. When pruning, always take the opportunity of cutting away dead and dying wood and the weak, thin growths on all shrubs, even those that do not normally require pruning. Watch out, too, for crossing branches and shorten one of them to prevent them from rubbing together in the wind.
REMOVAL OF SUCKERS
Azaleas, cytisus, rhododendrons, syringas (lilac), andare a few of the plants that are liable to produce suckers from below ground which must be removed.
If the plant is known to be a particular variety grafted on to a stock root of a commoner sort (for example, named varieties of lilac grafted on tostock), the suckers will only produce flowers of the type normally produced by the stock, and may be vigorous enough to replace the grafted variety eventually. To remove the suckers, dig carefully to the root from which the sucker springs and then cut the sucker off.
Other plants such as bamboos, cerato-stigmas, some clerodendrums, some cornus, fuchsias, some hydrangeas, some hypericums, kerrias, philadelphus,on their own roots, rubus, salix and some spiraeas spread by means of shoots produced from below ground.
Strictly, these shoots are suckers, but do not remove them unless it is necessary to keep the plant within bounds. To remove the suckers, cut round the base of the plant with a spade.
PRESERVING TREE SHAPES
Many trees produce unwanted growths or “feathers” from their trunks, which must be removed or they will quickly develop and spoil the shape of the tree. When training a young plant into tree shape, remove all side growths until the required height of trunk is reached; the plant can then be allowed to develop naturally and form a head. Many plants grown as shrubs are treated in this way, especially those that are required for lawn specimens.
PESTS AND DISEASES
Various pests such as aphids, leaf-rolling insects, sap-sucking pests, and leaf- and shoot-eating caterpillars do sometimes attack trees and shrubs. In some years these attacks may be fairly severe, particularly in the vicinity of large trees, but they can be controlled by routine sprays with insecticides such as derris, D.D.T., gamma-B.H.C, malathion or nicotine preparations.
If the plants are attacked by fungus diseases, which produce a grey, mould-like deposit on the leaves which is unsightly but seldom very damaging, spray them either with copper fungicides or with Karathane.
Spray forcefully, holding the nozzle so that the underside of leaves and the growing points are thoroughly wetted.
Many shrubs can be propagated from soft-wood cuttings taken in spring or early summer and rooted in a frame, or from hard-wood cuttings taken in autumn or early winter and rooted in a sheltered place out-of-doors. It is also easy to detach the rooted suckers of some plants (not those of grafted trees) for propagation purposes.
The pliable branches of some types of shrub often touch the ground and root where they touch. This is called a rooted layer, which can be detached and grown as a separate plant.
Themethod is often used to propagate shrubs whose branches are low enough and supple enough to be brought to ground level. A slight incision is made on the underside of the branch, which is then held in the with a stout wire pin or a stone.
Most can be raised from seeds, although some hybrids will not come true to colour or form. The seeds of trees and shrubs often take over a year to germinate, so do not throw away the pots in which seeds have been sown until at least two years after sowing.