December pruning of trees, shrubs and climbers
My gardening resolution this year is to keep on top of my pruning and that means getting out into the garden with my secateurs every month. The garden is at its most dormant right now, so it’s a good time to catch up on any pruning missed or forgotten since the autumn. If the weather isn’t favourable, you can leave it for a week or two, but make sure all winter pruning is completed before the sap starts rising during early spring. There’s still time to prune newly planted trees to remove any damaged growth and help balance the shape of the canopy as well as maintain a dominant main leader. Damaged and lop-sided growth can be removed from many established specimens too, but consult a professional tree surgeon before tackling anything substantial and make sure the tree does not have a preservation order on it before you start. Top of my list to prune right now are: ampelopsis, angel’s trumpets, bittersweet, bougainvillea, Buddleja globosa, Chinese trumpet vine, cotoneaster, deciduous barberry, Dutchman’s pipe, elder, Japanese laurel, Kilmarnock willow, kolomikta vine, ornamental pear, rubus, ornamental vine and wisteria
SHRUBS
Aucuba (spotted laurel)
Although fruiting spotted laurels are best pruned during March or April, non-fruiting male varieties, such as Aucuba japonica ‘Crotonifolia’, can be pruned now. Initially, prune back new growth by about one-third to promote bushy growth. Thereafter, little pruning is required except the removal of upright shoots that spoil the shape of the shrub and all-green reverted shoots on variegated varieties. Neglected old plants that have become woody at the base can be improved by cutting out one-stem-in-three each year starting with the oldest stems, until the whole plant has been rejuvenated. Apply a generous 5-7cm (2-3in) mulch of well-rotted garden compost or manure around the base of the plant after pruning. Spotted laurel hedges should be trimmed with secateurs rather than shears to keep them compact, since this will avoid leaving damaged foliage on the clipped hedge.
Berberis thunbergii, Berberis x ottawensis (deciduous barberry)
If you want to improve the display, these berberis should be pruned while dormant, ideally before the end of February. Being thicket-forming shrubs, they should have one-in-five stems cut out each year starting with the oldest to encourage vigorous young shoots from the base. If you are prepared to sacrifice some of the flower display you can improve the spring foliage effects and autumn colour even further by cutting out one-stem in three or even one-in-two at this time.
Brugmansia (angel’s trumpets)
Also known as datura, this highly poisonous shrub bears wonderful hanging trumpet flowers throughout the summer months. To keep the shrub flowering well and within bounds (particularly if being grown in a tub on the patio), prune all the growth made the previous year. Cut back to within 15cm (6in) of a stubby framework of branches.
Buddleja globosa
Budlejja globosa flowers on wood produced the previous year, so as a rule should only be pruned directly after flowering in June or July. However, neglected plants that flower out of sight high up on the bush or have become bare and unsightly at the base, can be rejuvenated by cutting back now. Although, next year’s flowers will be lost from the stems removed, new vigorous growth will be produced that will flower the following year. Very tall stems can be reduced by cutting them back to a sideshoot lower down and the whole plant can be rejuvenated by cutting out one-stem-in-three starting with the oldest. You’ll still get 66 percent of the flowers and a completely new plant within three years!
Cotoneaster
Prostrate cotoneasters, such as C. horizontalis, C. dammeri and C. microphyllus, can be pruned now to remove any shoots that disfigure their overall appearance. Spreading branches can also be thinned or cut back to keep these shrubs within their allotted growing areas. Cotoneaster horizontalis trained against a wall or fence should have stems that are growing away from the support removed, so that it fans out neatly.
Salix caprea ‘Kilmarnock’ (Kilmarnock willow)
This slow-growing weeping standard needs little or no pruning during its early years other than the removal of damaged or dead stems. However, once the crown of weeping stems starts to become congested, cut out one-in-three, starting with the oldest. If necessary, get under the umbrella of stems so that you can see what you are doing before making the cuts. If the remaining stems are nearly reaching the ground, cut the longest back to an outward-facing bud, removing about half their length.
Sambucus (elder)
Slow-growing ornamental varieties of elder require no routine pruning. Varieties of elder that are grown for their dramatic cut-leaf displays, such as the burnished gold ‘Sutherland Gold’ or the near black ‘Black Lace’ and ‘Black Beauty’, should be pruned annually from now until early spring so that they produce vigorous new growth and the most flamboyant foliage displays. Cut back all new growth to an established stubby framework of branches 15-45cm from the ground. To get taller plants, at the back of the border, say, make the framework 1or 2m or so high. Other elders can also be pruned now to keep them neat and tidy. To get flowers and berries cut out one-stem-in-three each year starting with the oldest.
TREES
Pyrus (ornamental pear)
All ornamental pears, including the popular variety ‘Chanticleer’, produce a single-leader standard with a pyramid-shaped canopy. No routine pruning is necessary except to remove badly positioned or damaged branches that unbalance the overall shape. Aim for evenly spaced side branches all the way around the trunk. Also remove lower branches over several years as the tree matures to create a clear trunk up to 2m (7ft). Even the weeping variety ‘Pendula’ needs a clear stem to allow sufficient room for the cascading branches.
CLIMBERS
Actinidia kolomikta (kolomikta vine)
Before new growth starts in early spring, kolomikta vines can be pruned to keep them within bounds. First, remove any crossing, diseased or over-crowded stems. Established plants should then have the previous year’s growth cut 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. Kolomikta 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.
Ampelopsis
This rampant climber needs plenty of space, but will still need to be cut back to keep it within bounds in most gardens. If grown against walls make sure the self-clinging stems do not block gutters, get under roof tiles or hinder the opening of upstairs windows. You can also grow it as a curtain of foliage down the sides of a pergola. In this case, cut back all new growth to within a couple of buds of the main framework now.
Aristolochia (Dutchman’s pipe)
No routine pruning is required, other than the removal of crossing or damaged stems. This is best carried out from now on, before buds break in spring. To restrict the size of established plants, cut back new growth to within a few buds of the main framework. Dutchman’s pipe also responds well to more drastic pruning so neglected specimens can be cut back hard at this time of the year by pruning the main framework to a younger sideshoot produced lower down each main stem.
Bougainvillea
To get the best displays, you need to train a framework of well-spaced branches up the support. During late winter or early spring, before new growth starts, cut back last-year’s growth by about two-thirds – pruning to a plump outward-facing bud. Remove any weak or misplaced stems completely. Once the climber has covered its support, cut back all new growth to just two or three buds from the established framework. Older plants can be invigorated by removing two or three of the oldest framework stems, cutting back to a younger sideshoot near the base. All other sideshoots that appear on the main framework should be pruned back to two or three buds.
Campsis (Chinese trumpet vine)
Prune Chinese trumpet vine in late winter or early spring before new growth starts, to promote flowering stems and to keep within bounds. Aim to create a framework of well-spaced branches over the supporting trellis or wires. Once the framework is established, cut back the previous season’s growth to just two or three buds from the established framework. Remove any weak or misplaced stems completely. Older plants can be invigorated by removing two or three of the oldest framework stems, cutting back to a younger sideshoot near the base. Campsis responds well to severe pruning, so neglected plants can be restored by cutting the whole framework back to within 30cm of the ground.
Celastrus (bittersweet)
No routine pruning is required other than the removal of crossing or damaged stems. Indeed, severe pruning will stimulate vigorous leafy growth at the expense of flowering shoots. However, new shoots and sideshoots that have grown beyond the support can be cut back to two or three buds from their base. Neglected plants can be cut back hard to within 30cm (12in) of the ground, but flowering will be reduced for a few seasons.
Rubus (ornamental bramble)
For the best ornamental brambles, prune each year during late winter or early spring. Flowering brambles such as R. odoratus, R. spectabilis and the popular variety ‘Benenden’ should have one-stem-in-three cut out each year, starting with the oldest stems that flowered during the previous year. To get the best displays from white-stemmed brambles, such as R. biflorus, R. cockburnianus and R. thibetanus, cut all the stems back to ground level.
Vitis (ornamental vine)
Once established, prune at this time of the year before the sap begins to rise to keep the plant within bounds, paying particular attention to stems that are encroaching on windows, guttering or roofs. If you are growing vitis in a restricted space, such as over a pergola, cut all the previous year’s growth back to 2 or3 buds from the main framework. Old and neglected plants respond well to severe pruning and can be cut back to plump buds about 1m from the ground at this time of year.
Wisteria
Wisteria is extremely versatile and can be trained against walls to form curtains of foliage and flowers or grown through pergolas where its pendant blooms can cascade overhead. It can even be trained to form impressive standards. No matter how you grow them, if you want to get a really spectacular flush of flowers you will need to prune them properly. This should be done twice a year, in summer and again in winter. During July, about two months after flowering, your wisteria will have produced masses of long wiry tendrils and if they are not required to extend the plant’s territory these should be roughly chopped back to within six leaves from where they join the main stem (this can just be done with a pair of shears if you like). Now you can cut these trimmed stems back to within two or three buds of their base. If you did not prune in summer you can still cut back the whippy stems now.
