Gardening: The challenge of exotica

There are flower buds on the branches of our mimosa. At least, I think they must be flower buds, for they look different from the growths that have produced only leaves since the plant was set against a west wall of our house two years ago. It may be wishful thinking, but I am sure there is a hint of yellow in the crunchy, mossy little eruptions in the angles where leaf stems meet the branches.

This is Acacia dealbata, the commonest of the mimosas and one of the hardiest. But even in the south of England it needs the protection of a sheltering wall to nurse it through the winter. Only in balmy Cornwall do you see mimosas growing happily out in the open, as they do in New South Wales and Tasmania. It came to this country from Tasmania in about 1820, but never liked our climate as much as it did the south of France, where it grows with native abandon.

It certainly grows fast. Already, the branches of our tree are brushing the sills of the bedroom windows, 15ft up. The leaves are lovely, pale greyish green, very finely cut and ferny. The whole plant moves liquidly in a breeze.

But fast-growing plants are often very brittle. As autumn breezes turn to winter gales, how will the acacia cope? As so often in the garden, the solution is a compromise. The two main branches have been pinned back hard against the wall; the smaller branches arising from them are uncorseted and free. It still moves but some protection is in place for the main framework.

Ever since plantsmen started bringing strange exotics into this country, gardeners have enjoyed the gamble of growing them. If the gamble comes off, you feel inordinately proud. If it does not, well, there is always another season.

November is a good month for planting trees and shrubs. Before everything was grown in containers, the lifting season started straight after Guy Fawkes night. Growth by then has slowed down, but the ground is still reasonably warm and receptive. Although above ground things seem to be dormant, roots will grow until the year end.

There is an obvious advantage in giving newly transplanted trees and shrubs the chance to settle down and find their feet before they are required to spring into leaf or blossom.

I prefer stock that has been grown in the old way in open ground rather than in containers. The roots are so much better. The network is more extensive and it is also better balanced. Roots of trees and shrubs coil if left too long in pots. You may try and uncoil them when you plant, but often they have lost interest in trying. They have been thwarted so long, they no longer care.

The other advantage of "bare root" plants is that they have always been used to coping with life as it really is. Their roots will have bumped their noses against stones and not taken offence. They will have learned how to worm a way through clods of hideous clay. They will be unfazed when winds blow and try to rock them out of the ground.

The roots of container-grown plants do not have to work very hard to infiltrate the soft, light, sifted compost they are planted in. They get used to the easy life, and the roots may never be brave enough to tackle the real earth around them when you plant them out. You might dig a big planting hole and mix compost with the soil but, at some stage, even that is going to run out and the roots are going to have to cope. Or not.

Choosing shrubs to plant against the walls of a house is tricky because you have to think whether the wall is sunny or shady, whether the ground is light or heavy, acid or neutral.

A west wall is generally considered a favoured wall. It will be protected from the most damaging kinds of wind. It may be in shade for the first part of the day, but will get plenty of sun in afternoon and evening. Because of its aspect, facing the setting sun, a west wall often provides a good backdrop for a sitting out place where you can slump happily with a drink and watch the sun go down.

If you can arrange billows of scent to waft over you while you are sitting, so much the better.

Flowers For The Wall

THE SCENTED wall shrubs listed below are all suitable for a west wall. They are some of my own favourites.

Trachelospermum jasminoides. The jasmine tag applies to the flowers, which are simple, white and richly scented, very like the common indoor- flowering jasmine, often wound round in hoops. They come in July and August, contrasting well with the leaves which are evergreen and slightly leathery. Growth is slowish, but will eventually haul itself up to about 10ft. It does not need pruning.

Rosa "Gloire de Dijon". By no means a trouble-free rose, not as vigorous as beefy modern varieties, nor free from black spot. But the scent is outstanding and the colour unparalleled, a soft, buff-apricot flower, fading as it ages. Each bloom is quartered like some other old-fashioned roses. This one was bred in France in 1853. It will reach 12ft.

Cytisus battandieri. This is a broom that looks like a laburnum and is worth growing for its foliage alone. The leaves are made up of three spoon- shaped silvery leaflets and have the dull, lustrous texture of expensive satin. To the touch, they are equally cool and slippery and the colour is olive-silver, more silver than olive on the youngest leaves. The dense domes of bright yellow flowers, smelling exotically of pineapple, appear in May and June. The shrub is evergreen, but the growth tends to be lanky with the best foliage onthe ends of the branches. Like other brooms, it will not produce new shoots from old wood. Do not try to cut it back. Replace it instead. Where it is happy, it reaches 15ft.

Clematis rehderiana. Not a showy clematis, but an intriguing one, best planted to wander through some existing wall shrub, such as a rose. In late summer and autumn it is covered with small, nodding, primrose-coloured flowers that smell of cowslips. The leaves are conspicuously hairy. Cut it hard back in late winter if you want to tidy it up.

Magnolia grandiflora. A very grand wall shrub that needs the promise of a long, undisturbed future. And not too many windows to get in its way. The evergreen leaves are glossy, like laurel but much finer. The creamy flowers can be almost 1ft across and start to appear in August. "Goliath" is the best cultivar, but you must buy plants that have been propagated from layers or cuttings, not grown from seed. Seed-raised plants can take more than 20 years to flower.