September pruning of trees, shrubs and climbers
As summer turns to autumn, thoughts turn to tidying the garden after the exuberance of summer and it is now an ideal time to prune many late-summer-flowering shrubs to keep them vigorous and flowering well. It’s also not too late to complete the pruning jobs for August if you haven’t got round to them yet. Here, I’ve given practical advice for pruning abelia, carpinus, embothrium, Jasminum officinale, lonicera and passiflora.
SHRUBS
Abelia
Young plants do not require any formative pruning after planting other than the removal of dead or damaged stems. In mild areas, where there’s little risk of winter damage, prune after flowering during late September or early October. Thin out congested growth by cutting back one-in-three stems that have produced flowers to a new sideshoot low-down or to near ground level. In cold areas or after particularly cold winters, much of the top growth may have been frost-damaged and in this case it is better to cut down all the shoots to near ground level during May. This is also the best way to rejuvenate old or neglected plants, but if you find this too drastic and you have the patience, cut out one-in-three flowered stems each year (starting with the oldest) over a three-year period instead.
Lonicera (shrubby honeysuckles)
There’s still time to prune shrubby honeysuckles, such as the popular evergreen L. nitida ‘Baggesen’s Gold’. Evergreen hedges should be cut back by removing about half the new growth each year until they reach the desired height. Thereafter, trim the hedge during May and again in September.
TREES
Betula (birch)
Birch trees need little regular pruning, but when they are young it is a good idea to cut off lower branches to allow a clear length of white trunk. Pruned before August they can bleed profusely, but if pruned now they sap flow will have slowed down.
Carpinus (hornbeam)
Deciduous hornbeam trees are best pruned during late summer because they are prone to bleeding if pruned in spring or early summer. Most hormbeam trees will form an attractive, well-balanced canopy without intervention and so require no pruning other than the removal of crossing or wind-damaged branches. Young trees should also be encouraged to produce a clear trunk, so remove lower side branches to gradually raise the canopy as the tree grows. They can be trained as standards, dense hedges or pleached to look like a hedge on legs. However, hedges should be trimmed in July to keep them neat and attractive throughout the summer. Cut back well-established hedges as required, but new hedges should be cut back only lightly.
Embothrium (Chilean fire bush)
Grown for its vivid display of brilliant red flowers, the aptly named Chilean fire bush requires little or no routine pruning, except the removal of dead or damaged stems. However, if left to its own devices it will form an attractive multi-stemmed shrub-like tree, so to create a specimen single stemmed tree you will have to prune it to shape. Remove all but the main stem and then keep pruning out any suckering shoots that are produced in subsequent years. You will need to either excavate a hole and cut the sucker at its origin with secateurs or cut it off with a judicious thrust of a sharp spade. Even multi-stemmed specimens benefit from being thinned out to the strongest four or five stems. Any routine pruning of wayward or straggly stems is best carried out after flowering during late summer.
CLIMBERS
Jasminum officinale (common jasmine)
This scented climber should be pruned after flowering during late summer. Aim to create a framework of well-spaced branches over the support. Twining stems will soon provide good coverage. Once well-established, cut back shoots that have flowered and are not needed to cover the support by pruning to a sideshoot or bud near the base. Common jasmine tolerates hard pruning so neglected plants can be reinvigorated by cutting back to within 50cm (20in) of the base.
Lonicera (common honeysuckle)
Most honeysuckles are deciduous and are best pruned after flowering during late summer, while evergreen Japanese honeysuckles (Lonicera japonica) should be pruned during early spring. Once the honeysuckle has reached the top of its support, tip-back the shoots to encourage flowering sideshoots to develop. Well-established plants can become over-congested if left un-pruned, so thin out the flowered shoots by cutting back by about one-third to a newer sideshoot lower down. Neglected plants can become a top-heavy mass of twining stems if not pruned regularly - with flowers out of sight on the top. Give it a short-back-and-sides, then reducing the number of main stems removing any awkwardly placed or crossing stems first. If you want a complete clear out, deciduous honeysuckles do respond well to hard pruning in winter to within 30cm (12in) of the ground, but you will have a big gap and reduced display for a few years.
Passiflora (passion flower)
To make the most of your passion flower (Passiflora caerulea) you will need to train and prune it carefully. Aim to create a permanent framework of branches that will produce a succession of flowering sideshoots. After planting, cut back plant to about 30cm (12in) to encourage plenty of sideshoots from low down on the plant. When training against a wall or fence, space out these stems as they grow about 15cm (6in) apart across the support. Keep tying in the stems until they reach the top of the support and then pinch out the growing tip to encourage sideshoots. On pergolas and arches, trim back all sideshoots except those near the top which can be trained over the support until the climber’s framework is complete. Thereafter, simply cut back shoots that have flowered and fruited to within two or three buds of the permanent framework of the plant. Replace old specimens with young vigorous plants rather than attempt renovation with drastic pruning.
Next month: liriodendron, malus, parrotia, parthenocissus, pyrus, quercus, santolina, salix, sorbus and many more.
