Climbers and Wall Shrubs
Climbers are plants with weak stems that take themselves up towards the light by means of their climbing habit. Plants have adapted themselves to this habit in a number of different ways:
1. By twining stems, as in wisteria.
2. By twining leaf stalks, as in clematis.
3. By tendrils, as with the(species of vitis).
4. By tendrils, producing pads that stick to their supports, as happens in Parthenocissus tricuspidata (Virginia creeper).
5. By roots produced on aerial stems which stick to their support, the best example being Hedera helix, (common ivy).
6. By thorns which hook on to support, as in climbing.
In addition there are plants, lax of habit, that get themselves up to the light by flopping over rocks, trees or other shrubs.
In the garden climbers can be used for a number of purposes: for covering pergolas, wall and fences; for training up poles; and for growing over or through trees and shrubs. One chooses the climber most suitable for a particular site. On a bare wall or fence only a climber that sticks itself to its support can be used, but if the wall or fence is provided with a trellis or parallel wires any kind of climber can be grown.
PLANTING AND TRAINING CLIMBERS
Climbers are now almost always container-grown and on sale throughout the year. Spring planting is the best, but planting can be done throughout much of the year as long as attention is paid to watering until the climber is established. After planting, reduce the stems to a half, or even a third, of their original lengths to encourage young growth to develop at or near to ground-level. Select three or five of the strongest shoots, provide them with canes, vertical wires or strings, and train them in the desired direction of the permanent support. At the end of the next growing season reduce all the leaders by about a half, cutting the weakest shoots even harder; thin out crowded shoots and space well on the main stems. Repeat each year until the allotted space has been filled with a well-spaced framework.
Regular attention is necessary in the training of climbers, and when growth is in spate they need almost daily attention. Clematis and other plants that have twining stalks, if neglected even for a week, produce an unmanageable tangle which defies even the patience of Job to unravel! Moreover, if climbers that stick to their supports – either by roots or sucker pads—are allowed to wander in the wrong direction, it means that the shoots must be pulled off whatever surface they have fastened on and they will not stick again.
Evergreens are treated similarly to deciduous climbers butis always less severe, the growth being tipped rather than cut hard back. Do ensure that the bases of walls and fences are adequately clothed to start with and keep them so.
PRUNING ESTABLISHED CLIMBERS
The same rules apply to pruning established climbers as for shrubs, that is the method and timing is dependent on the age of the wood on whichare produced. Those which flower on current season’s growth can be cut hard back to an established framework during the winter. More often they are cut to ground-level and in this case all the training pruning described in this section can be ignored. When pruned hard, flowering is delayed, but the flowering season may be extended by leaving in some shoots which are trimmed but not cut hard; these are removed completely the following year.
Climbers flowering on previous season’s wood are pruned after flowering. Shoots which have flowered are removed or cut back to where new growth is developing, and thinning out of remaining growth follows. Train in new shoots as they develop, keeping only enough to comfortably furnish; any surplus should be removed.
After a framework has been formed, the spur producers have all side shoots cut back to two or three buds during late winter. For some this treatment may have to be carried out twice, once in summer when shoots are cut to form fine buds and again in winter when any resulting growth is shortened back to two or three.
Climbers on poles need drastic pruning at all times, irrespective of the group to which they belong, to ensure that no more growth is permitted than the poles can support.
Climbers on trees, on the other hand, need no further pruning once they are established, unless growth becomes excessive and threatens the tree or if a clutter of dead wood occurs.
On pergolas pruning is minimal, just thinning out to prevent overcrowding and removing shoots which wave about in the wind and annoy people passing beneath. Some training in of young growth should be practised so that periodically some of the oldest stems can be removed.
SITING AND PLANTING OF WALL SHRUBS
An area close to a wall is more protected than one in the open, and of course drier. In summer walls absorb as well as reflect heat and so, being warm and dry, help to ripen wood.
A south wall is the warmest and driest and well suited to growing plants considered to be tender or needing to have their wood thoroughly ripened to flower freely. A west wall is almost as good. An east wall, however, is not suitable for early-flowering shrubs; flowers of many plants can withstand some freezing without damage as long as they can thaw out slowly, but winter or early spring flowers are likely to be damaged in the early morning sunshine on an east wall. Such a wall is better suited for the growing of sprawling orthan for plants considered to be tender.
On a north wall there is no direct sun, and so it remains moister with less fluctuation of temperature, hence cooler than a more open position. A north wall, therefore, is well suited to shade lovers and shrubs requiring cool, moist growing conditions in summer.
When there are south or west walls in the garden it is possible to be more adventurous in the choice of plants and to try out trees or shrubs which are classed as tender in a particular district for growing in the open. Shrubs which, when grown in the open, flower sparsely or not at all, especially after a wet summer when wood fails to ripen properly, often flower profusely against a wall. West and south walls offer protection to shrubs that flower in the winter months by allowing flowers to develop fully and remain open and undamaged by the cold.
Shrubs for planting against a wall may be offered bare-rooted, (with a ball ofin the case of evergreens), but many, and especially the tender ones, are now sold in containers. Planting is best carried out just before growth starts, which will be in early spring for some deciduous shrubs but in most cases mid-spring is preferable. Plant firmly, 23-30 cm (9—12 in) away from the wall, and finish up with a shallow depression in the soil around the main stem so as to facilitate watering, which should continue until the shrubs are well established – on each occasion giving a good soaking.
TRAINING WALL SHRUBS
Wall plants which are naturally trees can be trained to a single leader. A single-stemmed young plant should be chosen and headed back in spring to about 23 cm (9 in) above the lowest wire or 60 cm (2 ft) from the ground if on a trellis. Insert a strong cane or fix a vertical wire, up which the leader is to be trained.
In the following growing season, the uppermost buds will develop. Select the strongest and train in as a new leader. Take the next two shoots and tie one on either side of the leader to canes fixed in position at an angle of 45° to the vertical; any surplus shoots are stopped at four buds. In the following spring, lower the branches to an angle of 60° (keeping the side branches at an angle, allows extension growth to develop). Meanwhile the leader is beheaded at 23 cm (9 in) above the next wire or about 45 cm (18 in) above the first pair of branches when growing on a trellis. The strongest shoot is again tied in as the leader, and two more are tied in at 45° whilst surplus shoots are stopped at four buds. In the following spring again, the bottom pair of branches is brought to the horizontal, the second tier dropped to 60°, surplus shoots stopped at four buds and the leader again beheaded.
This practice continues until the uppermost wire or the top of the trellis is reached, after which the leader can be allowed to grow on. In the summer of the following year, the leader is then removed just above the top tier.
Once the bottom tier has been tied in horizontally, flowering can be allowed to take place. At all times any branches coming away from the wall are removed.
The above method is slow, but it builds up a well-balanced framework. Provides good cover low down and flowering is progressive.
The following is a simpler method, best suited for deciduous subjects, and while not as good as the one just described it produces results more quickly and still provides reasonable cover. On a single-stemmed young plant, cut a notch just above the buds into growth which is allowed to develop untied whilst the leader is tied to a central cane or wire. In the following springtime, the best-placed side branches are pulled down towards the wire and secured near the leader but not tied so tightly as to lie at the horizontal. Any surplus shoots are cut back to two or three buds. Notching again is carried out and the resulting shoots are allowed to grow freely whilst the leader is secured to its vertical support. In the next year, prior to growth starting, the lowest branches resulting from the first year’s notching are pulled down and tied at the horizontal. Those resulting from the previous year’s notching are again tied loosely. This continues up to the top of the wall when the treatment of the leader as already described is repeated.
Another method of training a tree, which is also well suited to most shrubs, is to produce a fan-trained framework. Plant a single-stemmed young plant and make a cut 90 cm (3 ft) from ground-level. Insert four canes, the lower pair at 45° and the upper at about 30° from the vertical, two on either side of the main stem. When growth starts, select the strongest four shoots and train up the canes, tying in at regular intervals. When planting a branched shrub select four stems and remove the remainder. Just prior to the commencement of the next growing season, cut back these four shoots to a third of their original length. Of the shoots produced, select two from each stem and tie to suitably fixed wires or string, pinching back the remainder. At the end of the next growing season there will probably be sufficient framework built up for shrubs, after which established pruning can begin.
Trees will need another season to complete the framework. Prior to the commencement of growth, all the leaders are reduced to about half of the length of wood produced in the previous season. Of the resulting growth, select only two shoots, pinching back the remainder. Space these out and tie into position; if there are too many shoots any that are crowded can be removed completely. Now that the framework is complete, established pruning can commence.
ESTABLISHED PRUNING OF WEAK SHRUBS
Tender shrubs and trees, especially evergreens, are usually allowed to develop with the minimum of pruning. In late spring cut out any winter damage, thin out crowded shoots, remove old flower stalks and cut back any shoots coming away from the wall. On tender shrubs pruning is usually carried out in spring when the danger of frost has passed.
Deciduous trees and shrub’s flowering on current season’s growth can be cut hard back to the framework although some young stems are left unpruned apart from a light tipping.
The pruning of deciduous trees and shrubs flowering on previous year’s growth is delayed until after flowering, when that growth which has flowered is removed, cutting back where possible to where new growth is breaking. Of the new growth, select only enough shoots to comfortably fill the available space and remove the rest. Those which are spur bearing will have all young shoots shortened back to two or three buds until a spur system has built up.
Irrespective of the type of pruning, periodically train in some new shoots into the framework so as to be able occasionally to remove some of the oldest wood.