August pruning of trees, shrubs and climbers
Late summer is the best time to prune many midsummer-flowering shrubs to keep them vigorous and flowering well. It is also the ideal time to prune several trees that are prone to bleeding if pruned at other times, and it’s not too late to complete the pruning jobs for July if you haven’t got round to them yet. I’ve given practical advice for pruning Buddleja alternifolia<, buxus,="" callistemon,="" elaeagnus,="" x="" fatshedera,="">Genista hispanica, Grevillea, Helianthemum, Laurus, Nerium, Philadelphus, Pyracantha and Thymus.
SHRUBS
Buddleja alternifolia
This elegant deciduous shrub bears its scented flowers on stems produced the previous year. So to ensure good flowering next year you need to prune immediately after flowering is over, which can be anytime from late June to the beginning of August. Remove any dead or damaged growth and shorten lop-sided or over-long shoots to balance the overall shape of the shrub. Old and neglected shrubs can be rejuvenated by cutting out one-in-three stems, starting with the oldest. Either cut them back to a sideshoot lower down or remove them completely. You will loose some flowering shoots for next year but the shrub will be the better for it in subsequent years. Alternatively, cut back two-thirds of the oldest stems immediately after flowering.
Callistemon (bottlebrush)
The flowers of this exotic beauty are produced on the tips of new shoots. Encourage bushy growth when young by tip-pruning after flowering in summer. Well established plants do not usually need routine pruning, but if they out-grow their allotted space or have become neglected, they can be reduced in size by pruning in stages over two or three summers, cutting back older wood to younger, outward-facing shoots immediately after flowering. This will encourage new shoots from the base.
Elaeagnus
Deciduous Elaeagnus angustifolia and E. umbellata varieties require little routine pruning other than the removal of dead or damaged stems. Old and neglected plants can be rejuvenated by cutting back one-in-three stems, starting with the oldest. Give hedges their final trim next month. Evergreen varieties of Elaeagnus x ebbingei, E. glabra, E. macrophylla and E. pungens require little routine pruning other than the removal of dead or damaged stems. Overly long shoots that spoil the shrub’s shape can be cut back to a bud using secateurs. Remove any plain green-leaved shoots as soon as they appear, cutting them back to their origin. Evergreen hedges can be trimmed at this time of year too.
x Fatshedera
This hybrid between Fatsia and Hedera makes a splendid evergreen groundcover plant in mild areas. It can also be trained as a standard and as a climber. Little or no pruning is required other than the removal of wayward shoots and stems damaged by frost. At this time of the year, cut back vertical shoots on groundcover plants to keep them neat and compact and trim and tie in shoots on trained forms.
Genista hispanica (broom)
These spreading deciduous shrubs put on a fabulous show in early summer on stems produced the previous year. To retain the plant’s bushy shape lightly trim the flowered stems immediately after flowering. Do not prune back into woody stems because they are unlikely to re-sprout and never prune back hard since this may kill the shrub. Do not prune Genista lydia at all, since this does not respond to being cut back. Old and neglected shrubs are best replaced.
Grevillea
In mild areas this exotic evergreen shrub can form an attractive summer-flowering specimen. Little or no pruning is required other than the removal of wayward shoots and stems damaged by frost. You can encourage a bushy habit by lightly prune the tips of new growth once flowering has finished. Trim informal grevillea hedges at this time of year too.
Ilex (holly)
Bushy evergreen hollies such as Ilex crenata as well as holly trees trained as hedges, such as the common or English holly, can be pruned to shape now that the growth has stopped but before the stems are fully ripened. It is important to leave the pruning of formal hedges to this time to avoid re-growth that will spoil the hedge’s neat outline. Always use a pair of secateurs so that you can avoid damaging the leaves that remain on the hedge after trimming. Remove any plain green-leaved shoots on variegated varieties as soon as they are noticed, cutting them back to their origin.
Laurus
Little or no pruning is usually required on informal shrubs, other than the removal of dead or damaged stems. However, you can keep topiarized shrubs neat and rounded by pruning new growth back using a pair of secateurs. Bay laurel trained as standards will need any new shoots cut from the main stem. Hedges can also be trimmed for the second this time of year.
Nerium
In mild areas this borderline-hardy evergreen shrub requires little or no pruning other than the removal of wayward shoots and stems damaged by frost. You can encourage a bushy habit by lightly pruning the tips of new growth once flowering has finished.
Philadelphus
Several philadelphus can be pruned at this time of year. You can prune mock orange (P. coronarius) now that flowering has finished to improve flowering for next year. Cut back flowered stems to a sideshoot that hasn’t produced flowers or to a plump bud. Congested plants can have one-in-three stems removed, starting with the oldest. Old and neglected plants can be rejuvenated in the same way. Alternatively you can prune in spring to get the best foliage displays. To ensure good flowering on Philadelphus ‘Belle Etoile’ and ‘Virginal’ which bear their blooms on stems produced the previous year, prune immediately after flowering is over. Well-established shrubs should have one-in-four stems removed, starting with the oldest. Either cut them back to a sideshoot lower down or remove them completely. Feeding the plant after pruning will help encourage vigorous growth. Old and neglected plants can have all old stems cut back to ground level in winter or early spring. You will loose some flowering shoots for next year but the shrub will be the better for it in subsequent years.
Pyracantha (firethorn)
Although pyracantha is normally pruned in mid-spring, wall-trained specimens can be pruned for a second time at this time of the year to expose the developing fruit to make the most of the berry display.
Sophora
No routine pruning is usually necessary, other than the removal of dead flowers or damaged stems. This is best carried out during midsummer when the cuts are less likely to bleed. Wall-trained specimens need tying into their support and any wayward stems cut back or removed completely. Old and neglected plants are best replaced.
Thymus (thyme)
Little routine pruning is necessary other than the removal of dead or damaged stems. All plants should be rejuvenated by cutting back after flowering using garden shears to retain a neat, compact shape. But do not cut back into old wood since it is unlikely to re-sprout. Remove any plain green-leaved shoots on variegated varieties as soon as they appear, cutting them back to their origin.
TREES
Laburnum (golden rain)
Laburnums are best pruned during late summer because they are prone to bleeding if pruned in spring or early summer. However, you can also prune them anytime up until Christmas. Laburnums make excellent specimen trees or can be trained as an eye-catching standard or over a sturdy arch or pergola to help show off their spectacular flower trails. Specimen trees should only be pruned to improve the shape of the canopy and to remove damaged stems, while trained forms will need regular pruning to maintain the shape of the plant so that the flower trusses can be clearly seen. Take care to remove any shoots that appear from below the graft on grafted trees. Laburnums are prone to cavities after severe pruning if the collar at the base of the branch is damaged or stumps are left behind. For this reason it is worth raising the canopy when the tree is still young and keeping the stem clear as it grows.
Populus (poplar)
Most poplar 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. Also remove any suckers back to their origin unless you are growing the tree as a windbreak, in which case the suckers will provide protection right down to ground level. Old and neglected trees do not respond to hard pruning and are best replaced.
CLIMBERS
Billardiera
No routine pruning is required, other than the removal of crossing or damaged stems. Overgrown plants can be thinned by cutting back unwanted shoots to within a few buds of the main framework. This can be done now (after fruiting) or during early spring.
Clianthus (lobster claw)
Commonly called lobster claw or glory pea, this frost-tender evergreen climbing shrub can be grown outside in mild areas, where it will bear its distinctive flowers from spring to midsummer. Although no routine pruning is necessary, pruning when young and careful training will improve the overall display. Pinch out the shoot tips after planting to produce bushy growth from the base, then tie in new growth to the support. Once the support is covered, prune now that flowering is over to restrict its size and to remove any dead or damaged stems. Do not prune too heavily. Reduce older stems by about one-third to just above a well-placed side shoot lower down.
Hydrangea petiolaris (climbing hydrangea)
The climbing hydrangea is a popular, vigorous, deciduous plant that can be used to light-up north-facing walls with glossy foliage and heads of creamy white summer flowers. Although it can take a few years to get established, once it starts climbing there’s no stopping it. Little or no routine pruning is required, apart from removing the flowered shoots at this time of the year. To keep within bounds, prune back wayward shoots to a sideshoot lower down during the dormant season. Old and neglected plants can be cut back hard in winter, although you will miss out on the flowers for a few years.
Schizophragma
Little or no routine pruning is required, apart from removing the flowered shoots as they fade. Long, vigorous shoots can be cut back to a sideshoot lower down. Old and neglected plants do not respond well to severe pruning, so cut back over several years by removing one older shoot back to a new sideshoot near to the base each year and cut back overly long shoots by about one-third to keep the plant within bounds.
Next month: abelia, betula, carpinus, Jasminum officinale, lonicera and passiflora.
