Any nurseryman will confirm that the one of the most common problems gardeners ask them about is the less-than-exuberant performance of climbing plants: wisteria with plenty of growth and no flowers; clematis with a topping of flowers and bare stems; honeysuckle and jasmine that grow into dense thickets of woody stems. The solution to all these problems lies in both pruning the plant correctly, and in training it against its support in a way that encourages flowers rather than foliage.
To get most climbers to flower well it is essential to begin forming the basic shape you want the plant to grow into as soon as it is planted. Plant climbers that are to be grown up the side of a building about 50cm away from the wall so that are not in the dry area under the eaves of the roof. Use bamboo canes to support new shoots and to guide them into the area you want to cover. Horizontal stems produce more flowers and fruit than vertical ones, so begin to tie stems along horizontal wires, across trellis or along the cross-bars of a pergola as soon as they reach them. On walls and trellis, allow further stems to grow taller before turning them horizontally and tying them in.
Wisteria is a very vigorous plant that will produce lots of long, whippy shoots which, left uncontrolled, can dislodge roof tiles, clog gutters, and creep into attics. And, worse, they won’t produce any flowers. In August tie-in any stems that are needed to fill in gaps against the wall or to extend the plant over a pergola. Cut back all the rest to about 30cm from the point that they have grown from. Some gardeners leave this job until the following spring, but doing it now not only makes wisteria look neater, it also lets the sun into the plant to ripen the young stems. This is important for future flower-bud production.
The following February, shorten the stems that you pruned in the summer to about 5cm from the old wood. Doing this will create short, stumpy shoots known as spurs. If you look closely at these spurs there are usually two sizes of bud: short thin ones and fat, plump ones. The plump ones are the flower buds; the thin ones will produce more shoots. More long shoots will have grown since the summer. Prune these back to four or five buds from the main stem, making the cut just after a bud. February is also the best time to tackle wisteria branches that are growing away from the wall or to remove old, woody branches from mature plants. Saw these off just above a young, vigorous branch or shoot. If the branch is very long, remove it in sections.
In an attempt to simplify the pruning of clematis, nurseries classify them into one of three groups, each with distinct pruning requirements. This grouping is based on the parentage of the plant and when it flowers. If you don’t know what group a clematis belongs to, just prune it in relation to when it flowers. Very early, spring-flowering and evergreen clematis only need pruning to remove damaged stems and to keep them contained to the size you want. Large-flowered forms, that flower in May and June, should have their stems cut back to a pair of fat buds in February. Later-flowering clematis, those that start flowering in late June and July, should be cut back hard. Remove all the growth to a pair of buds about 30cm from the ground in February or early March. The first time you do this it can be unsettling – especially when you can see new growth appearing further up the stems you are cutting off. But hold your nerve, cut the whole plant down and a few months later you will have lots of young, fresh vigorous growth covered in buds and flowers.
It is essential to train the stems of climbing roses horizontally in order to produce a good display of flowers. Place supporting wires about 30cm apart and tie the stems along them with soft string at 30cm intervals. If you are growing the rose up a post or a pergola, wrap the stems around the support: stems allowed to grow straight upwards will be bare of flowers. Once the rose is established and you have covered the wall, cut off unwanted growth at its base and remove faded flowers. Prune-back side shoots by about two thirds of their length in the autumn. Old, woody stems should be cut back at their base to a new shoot and the growth from this subsequently tied in to fill the gap.
The passion flower, Passiflora caerulea, and both winter-flowering and summer-flowering jasmines, are spirited plants that need to be taken in hand if you want to prevent them becoming too rampant. Cut all the old, flowered stems of passion flowers back to the ground (or back to the main trunk if you are growing it over a pergola) in the early spring. At the same time cut lateral shoots back to about 15cm long. Immediately after jasmines have flowered cut all the stems that have had flowers on right back to the base. This can sometimes feel too drastic, and it is tempting to simply shorten the stems to form an attractive shape to the plant, but this will merely lead to a dense, congested shrub.
Climbers that require little pruning other than removing damaged shoots in the spring and thinning-out congested stems back to the base: Abeliophyllum, Actinidia, Billlardiera, Fremontodendron, Eccremocarpus, Hydgangea petiolaris, Lonicera japonica, Parthenocissus, Sollya.
To prune tall climbers you will probably need to use one of the most dangerous tools in the garden, a ladder. It sounds improbable, but ladders are one of the biggest causes of accidents in the garden: every year about a dozen people die from falls from ladders. If you are using a ladder against the wall of a house it is worth taking the time to tie it in, and to have someone at the foot of the ladder to steady it. Step ladders should always be placed on solid ground, never directly onto the soil: I can verify that falling even a few feet off a step ladder hurts like hell and is very undignified.