May pruning of trees, shrubs and climbers
Most shrubs, trees and climbers are in full growth at this time of the year, but don’t be in a hurry to put away your secateurs because there are still pruning jobs that can be carried out this month. It’s still not too late to check all plants over for signs of winter damage and take remedial action if necessary. Also, May is the ideal month to prune Abelia, Akebia, Aloysia, Arbutus, Berberidopsis, Chaenomeles, Choisya, Early flowering clematis, Helichrysum, Hibiscus, Lonicera, Prunus, Ribes and Ulex, and it’s not too late to complete the pruning jobs for April if you haven’t got round to them yet.
TREES
Arbutus (strawberry tree)
The strawberry tree requires little or no routine pruning other than the removal of damaged or dead stems. Although very hardy, winter damage can occur and is worth cutting this out after the threat of frost has passed. Established specimens can be trained into attractive trees by removing the lowest branches as the tree grows, slowly raising the canopy. This not only brings the attractive flowers and fruit up to eye level, but on Arbutus menziesii helps to reveal the tree’s naturally attractive bark.
SHRUBS
Abelia
Young plants do not require any formative pruning after planting other than the removal of dead or damaged stems. Once established, check plants over during late spring after the danger of frost has passed and remove any winter-damaged stems. Also 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. 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. In mild areas, where little winter damage has occurred, leave pruning until autumn after the shrub has flowered.
Aloysia triphylla (lemon verbena)
Frost-tender lemon verbena will usually survive in most gardens if it is given a sheltered spot. To keep your plant producing young and vigorous new growth, cut all stems back to plump, healthy buds about 15cm from the ground after the threat of further frosts have passed. In very mild areas, you may be able to create a shrub-like plant by cutting back to a stubby framework.
Chaenomeles (Japanese flowering quince)
Japanese flowering quinces are tough plants that can be left to their own devices. However, if you do carry out a little judicious pruning at this time of year you can improve the flowering display and overall ornamental appearance for the following year. After flowering is over, remove any dead or damaged stems and cut back new growth to four to six leaves. This is particularly important for wall-trained shrubs but works well on free-standing specimens too. This type of pruning produces flowering spurs. In time these spurs may become congested and require thinning out. Any overly long or wayward shoots that are growing away from the support on wall-trained shrubs should be cut out completely. Old and neglected specimens can be rejuvenated over a five-year period by cutting back one-in-three of the stems each spring, starting with the oldest.
Choisya (Mexican orange blossom)
This mound-forming evergreen shrub, which produces fragrant white flower in spring, needs no routine pruning other than the removal of any frost-damaged stems and uncharacteristic shoots that disfigure its overall shape and appearance. These are best removed completely or cut back to a side shoot lower down, before buds break in early spring. You can encourage a second flush of flowers on established plants by cutting back stems that have flowered by about half. Old and neglected specimens can be rejuvenated by pruning back hard during spring.
Helichrysum
The popular grey-leaved curry plant (H. italicum) and half-hardy trailer Helichrysum petiolare, which is often used in containers and hanging baskets, are both worth pruning at this time of the year. Both should be checked in spring to remove any frost-damaged stems and woody growth. Also reduce the length of sprawling stems to prevent the shrubs from becoming straggly. Helichrysum petiolare can be encouraged to produce fresh bushy growth by pinching out the tips of new growth from late spring. Old and neglected specimens of all other helichrysums can be rejuvenated by pruning back hard during spring.
Hibiscus
All types of hibiscus can be pruned during late spring. With the hardy shrubby mallows (H. syriacus) such as the popular ‘Blue Bird’ and ‘Woodbridge’ as well as the tender Chinese hibiscus (H. rosa-sinensis) little or no annual pruning is needed, other than the removal of dead or diseased stems and thinning out congested growth. You can also remove branches that have outgrown the available space or are making the overall shape lopsided.
Lonicera nitida (poor man’s box)
This small-leaved, evergreen lonicera makes an excellent hedge. During the first spring after planting, cut back all stems by about one-third to a half to encourage bushy growth. Once established, hedges will need trimming several times each season to keep neat, starting in late spring. Free-standing shrubs will require little or no pruning other than to keep them within bounds. Old and neglected specimens that have become bare at the base can be rejuvenated by pruning back hard during spring.
Prunus (laurel)
Laurels, such as Prunus laurocerasus and P. lusitanica can eventually reach tree-like proportions if left unpruned for many years. However, they can be kept within bounds and make excellent hedging and screening plants if you are prepared to prune them annually at this time of year. During the first spring after planting, cut back all stems by about one-third to a half to encourage bushy growth. Once established, little pruning is necessary other than to keep them within bounds. Hedges should be pruned during late spring and again in late summer using secateurs rather than hedge trimmers or shears, which will leave unsightly damaged leaves on the hedge after pruning. Old and neglected specimens that have become bare at the base can be rejuvenated by pruning back hard during spring.
Ribes speciosum (fuchsia-flowered gooseberry)
Like other flowering currants, these are best pruned annually to keep them vigorous and free-flowering. Cut back immediately after flowering during late-spring. Remove one-in-three stems starting with the oldest. Neglected shrubs can be rejuvenated in the same way during late winter.
Ulex (gorse)
During the first spring after planting, cut back all stems by about a quarter to one-third to encourage bushy growth. Once established, tip back new growth after flowering each year, using shears, to keep growth dense. Old and neglected specimens often respond well to severe pruning and can be rejuvenated by cutting back hard to 15cm of ground level.
CLIMBERS
Akebia quinata (chocolate vine)
This vigorous climber needs no routine pruning other than the removal of dead or damaged stems. Once established, chocolate vines can be kept within bounds by pruning once every few years during late spring. Prune the previous year’s growth back by about half its length, cutting back to an outward-facing bud. Neglected plants also can be rejuvenated by cutting back the mass of tangled growth with shears, then pruning the stems back to a healthy bud near to the main framework of branches. Chocolate vines even respond to drastic pruning – thinning or lopping out some of the main framework of branches at this time of the year to a younger sideshoot lower down on the climber.
Berberidopsis (coral plant)
During the first spring after planting, remove any dead or damaged stems. Once established, little or no pruning is required, other than the removal of weak stems and the thinning out of congested plants. Old or overgrown plants do not respond well to severe pruning so are best replaced if they look untidy.
Early flowering clematis (Group 1: winter- and spring-flowering clematis)
During the first spring after planting, cut back all stems to a plump pair of buds about 30cm above ground level. This will encourage more shoots to be produced from the base for the next year. You may miss some flowering in the first two years, but a much stronger plant will result. Once established, these early-flowering clematis (such as C. alpina, C. cirrhosa, C. macropetela and C. montana varieties), bear their flowers on growth produced in the previous season, so need little or no pruning. However, if you want to restrict the climber’s spread, prune overgrown stems back annually after flowering during late spring - cutting back to healthy pairs of buds. Subsequently, train in any new growth into the support.
