Training Climbing Plants for the Greenhouse
A fewin the greenhouse will greatly enhance its appearance. Choose from plants that are small and compact and can be fitted into the tiniest space, or from others that will cover a large area. Some will grow quickly from seed, some are , and some become steadily more beautiful as the years pass.
The description ‘climber’ is often loosely used to include plants that could more properly be called wall shrubs — plants that are unable to support themselves by tendrils or by twining. Special provision has to be made for supporting them and training them into the required shape. Nearly all climbers, however, will need some support; very few can be left to ramble without some artificial means to hold them in position.
A common characteristic of climbers is that they tend to be rampant and rather too vigorous. Left to themselves (and perhaps given too much food and water) they may become a tangle of stems and foliage, producing little in the way of flowers. This is especially true of perennials that are planted in a border of groundin the greenhouse or given excessively large pots.
The first cultural hint, therefore, is to use relatively small pots or containers, or restrict root spread in the ground by planting in a plunged clay pot or placing slates, tiles, bricks or asbestos sheeting around the sides of the planting hole when it is made. For most annuals an ordinary flowerpot 13-25cm (5-10 in) in diameter is satisfactory — depending on the expected (or required) ultimate size of the plant.
Selecting the support
When it comes to supporting, training and displaying the plants there are a number of points to be considered. Often the nature of the plant will suggest the best method, while in other cases there may already be a support in existence for which you need to choose a suitable climber; for example you may wish to cover a lean-to greenhouse wall or a roof-supporting column, pillar or post.
If you intend to plant permanent wall shrubs or climbers, then first pay some attention to the wall itself. A brick wall, or similar rough surface, is best rendered to give a smooth finish, filling in all holes so that there are no crevices where pests or diseases may accumulate. A coat of white vinyl emulsion or exterior paint will give a background that is both hygienic and pleasing.
To give wall support, attach wires to masonry nails driven into the wall or to screws fixed with plugs. Or you can use plastic-coated wire netting or mesh (obtainable in white for white walls) fastened to a wall or other part of the greenhouse structure. Plastic mesh without wire reinforcement is also sold for the support of climbers, but is less advisable for long-term use, as some plastics become brittle with age (especially in a sunny greenhouse) and may then collapse under the increasing weight of a growing climber. For a similar reason perishable materials like string or canes should be avoided for perennial climbers.
If you want your climber to grow up into the greenhouse roof, train it along wires stretched from end to end of the building, fastened to the glazing bars. For very small climbers, and particularly annuals, bamboo canes are suitable. You can usually insert several in the pot and arrange them like the spines of a fan. Small plastic mesh supports, intended for inserting in the flowerpots of house plants, are also convenient. For fastening stems to supports, a number of ‘patent’ plant ties are sold in garden shops. These are neat and secure and most can easily be moved from place to place.
Several delightful climbers will flower in the first year of sowing and planting. Ipomoea tricolor (rubro-caerulea), better known as morning glory, has long been prized for its glorious, large, blue, convolvulus-like blooms borne freely each morning but fading by early afternoon. In recent years varieties with new colours have been introduced, such as the blue and white striped Flying Saucers, the mauve Wedding Bells and the deep, rose-coloured Early Call that also has very long-lasting flowers. Sow seed in a warm propagator in mid spring (March) and transfer singleto 13cm (5 in) pots or several to larger pots. Well-grown plants will reach about 1.8m (6 ft) high in one year and become smothered with bloom.
Similar in height and vigour is(cup and saucer plant) — so called because of the flower shape. The flowers are deep violet, but a rare white form is said to exist. Another fast-grower is (Chilean glory flower). Provided it is sown early it will flower the same year, and it is hardy in sheltered places in mild areas although not often a long-lived perennial. It bears masses of showy, vivid orange flowers.
Some people like to grow sweetunder glass especially for cutting, but not all varieties are suitable. Choose types that flower in late autumn to early winter (October—November) and Cuthbertson varieties. With care the large-flowered Spencer varieties can flower well, but rarely before late spring (April). In all cases there is a tendency for buds to drop and a greenhouse with good light is vital to success. All plants must be stopped at the seedling stage.
Extremely easy (even for children) to grow, is the lovely little climber Thunbergia alata (black-eyed Susan). Even the small seedlings are impatient to flower and at this stage the best bright orange colours with jet black eyes can be selected for growing on. Inferior colours can be discarded if desired. Growth will only reach lm (3 ft) or so and there is usually room for this climber in the smallest greenhouse.
Striking and exotic, and much easier to grow than most gardening books imply, is Gloriosa rothschildiana (glory lily). This is grown from a long tuber that can be planted late on in spring (April) when the warmer weather keeps up the greenhouse temperature. Pot so that the blunt, roundish end is at the centre of an 18cm (7 in) pot. It is from here that the roots and shoots will grow. Just cover the tuber with potting; it does not matter if the pointed end protrudes above after placing the tuber longways. The plant will support itself by tendrils formed at the end of the leaves but will nearly always need further assistance from the grower. The flowers are like reflexed , with bright crimson and yellow flowers from summer to autumn. Over winter store them, completely dry, with the pots on their sides. Usually at least two new tubers will be formed and can be separated when replanting at the appropriate time the following year.
Some climbers are best bought as small plants (usually rooted) from a garden centre, nursery or gardening shop. Being perennial they may take several years to reach full flowering size but, like most climbers and wall shrubs, are a wonderful sight when in bloom. Bougainvillea is among the most showy and colourful. In this case it is the bracts and not the flowers that make the long-lasting display. There are a number of named hybrids of Bougainvillea x buttiana, and B. glabra is also popular. The colours range from orange to mauve shades and even young plants will cover themselves with bracts. Bougainvilleas can be trained as wall shrubs or the stems led up along wires in the greenhouse roof when the plants have reached sufficient height. A winter minimum of about 10°C (50°F) is advisable for best results. Pruning should be done in early spring (February) by cutting out all weak growth and cutting back to keep the desired shape.
A very vigorous but popular jasmine for the greenhouse ispolyanthum.
It has creamy-white flowers during late winter (January) and is extremely powerfully scented. To prevent rampant growth the roots are best restricted by growing in 25cm (10 in) pots. Do not be afraid to prune or cut back at almost any time, otherwise this climber can smother everything. It is ideal if you have a large area to cover but when strictly controlled is also suitable for a small greenhouse. A winter minimum temperature of about 7°C (45°F) is adequate.
A superb fragrant climber is Stephanotis floribunda, sometimes sold as a house plant trained around a wire hoop. In the greenhouse it will grow up into the roof and the waxy white tubular flowers, delightful because of their scent, will hang down in clusters. This climber likes a rather humid atmosphere and a winter minimum of about 10°C (50°F). It will survive lower temperatures if kept on the dry side during the cold months. Hoya carnosa also likes a fair degree of humidity. It is sweetly scented and has umbels of pinkish, starry flowers. The foliage is evergreen and there is a form with cream-margined leaves, greatly enhancing its beauty. Although surviving winter at about 7°F (45°F), best results are obtained if 10-13°C (50-55°F) can be maintained. It does well in shade and little pruning is required. Both stephanotis and hoya greatly benefit if you spray them with tepid water from time to time during summer.
Other popular climbers
A very beautiful evergreen climber for a greenhouse just kept free from frost is Lapageria rosea (Chilean bell-flower). Large, red tubular flowers of waxy texture are borne during autumn. It is a good choice for a shady greenhouse, even a north-facing conservatory or lean-to. The plants need little pruning and are happy in 25cm (10 in) pots. Pink and white forms are sometimes available but are not common.
An easy wall shrub for a frost-free conservatory is Plumbago capensis. This has either blue or white phlox-like flowers from spring to autumn. Pruned sparingly it will reach a height of at least 3.5m (12 ft) and looks most impressive if a blue and a white form are grown together and allowed to intermingle. When flowering is over, prune back all growth by about two-thirds.
Abutilon megapotamicum is a quaint, almost hardy climber with dainty red and yellow lantern-like flowers borne from spring to autumn. It is a good choice for a pillar or roof-supporting column, and demands little attention. Popular, but not a very wise selection for the greenhouse is Passiflora caerulea, the common passion flower — which is, in any case, perfectly hardy. Far better for under glass is the species Passiflora quadrangularis (granadilla), with much larger, exotic flowers, and other warmth-loving species when available. These need 10°C (50°F) in winter and moderate humidity. They are best trained along wires and if you don’t let the shoots become too long, then the flowers can be kept reasonably low.