When one considers the enormous, but entirely worthwhile effort which has to be put into giving a flat garden the invaluable interest of contours, anyone with a sloping site should bless his lucky stars — or the ice age. Because there is no doubt that the visual and actual movement offered by banks, steps and ramps adds immeasurably to a garden. Nevertheless, as in everything, all is not light and joy; maintenance can be difficult and access complicated. Yet if the situation is taken from the first as being essentially desirable, it almost certainly will become so.
The ideal site, of course, is one which falls from the house to the south or south-west. Such spots catch all the sun and, what is often most important, warm up early in spring. The fact that the house is to the north and somewhat higher conveniently provides protection from the coldest quarters as well. Keen gardeners moving house could do worse than to search for such a position. Any place with these advantages must capitalise upon them: sun-loving Mediterranean plants on the terrace, tender climbers (relative to the part of the country concerned) on the house.
It would be immoral not to use such opportunities to extend the usual range of plants seen.
Associated with this type of site is the likelihood of a worthwhile view stretching out below and ahead. This in turn causes problems of exposure to every wind which blows from the open quarter. Keeping the view or protecting the place are not easily reconcilable. Fortunately the choice is not usually so absolutely black and white, but if it has to be taken the balance is best made in favour of the view, finding plants which accept the conditions. Happily this is not really difficult. Exposed sites are discussed further in a separate section.
As with any site an early decision has to be made concerning the amount of ground to be actually cultivated, whether this is for flower borders or vegetables. On sloping terrain the decision is especially vital for while it is not difficult to find good plants to cover banks permanently it is not reasonable to expect frequently to dig or hoe any slope of more than a one in ten incline. Even this is much steeper than desirable. The disadvantages are obvious. Apart from the physical difficulties of actually doing the work, soil is washed down the slope during periods of heavy rain and, much more insidiously, there is a continual leaching of plant foods from the upper part of the piece of ground to the lower. If the slope does not end here there is then a continual nagging pain: the knowledge that one is fertilising next door’s garden. Few things could be more maddening — especially if their vegetables are recognisably better. Small things, such as running rows along the contours, rather than up and down the slope, and digging similarly help to prevent serious run off, but can only be taken as something of a cosmetic palliative.
The answer is obvious: to terrace.
Only the expense and effort has prevented the statement being made earlier. But the nettle has to be grasped, perhaps literally. The days are well past when a couple of local men would dig away for half a winter at little cost; today has brought in their stead a JCB excavator which can remove most of the garden in a day. Such aids, employed with care, make the problems of terracing much less daunting. A skilled operator can work one of these dinosaur-like creatures as delicately as one can wish, but it is vital that he knows exactly what is required. Vital, too, is care with established trees. Everyone knows that excess root damage will weaken and even kill a tree but less care is often given to ensuring that none of the trunk is buried when earth moving takes place. If the level of soil is to be raised and a mature tree kept, it will need its own surrounding retaining wall to maintain the same soil level.
Topsoil is invaluable — it has taken millennia to build up as the perfect medium for growing plants — it must not be lost. Even under a few inches of subsoil it loses its structure and full value. This, then, must be scraped off the area to be terraced and safely stacked. The operation which follows is one of cutting and filling — a lower ‘wedge’ lifted and reversed on to that above, giving an upper and lower horizontal area separated by a vertical ‘wall’. The topsoil is then returned.
This gross simplification needs a certain amplification. Firstly, if natural structure and drainage of the soil is not to be impaired, movement of any large machinery must be as restricted as is consistent with doing the job. Secondly, the new vertical face of soil does not, naturally, stay up by itself. A retaining wall has to be constructed and steps will be necessary to link the upper and lower levels.
As discussed in the section on****** paved areas, steps and construction of walls near to the house should, be in similar materials to it or in something complementary. And while this is still desirable with retaining walls, where the slope falls from the house any such wall will be hidden from it; this does provide a certain leeway. Walls built above ground only have to support themselves, but it must be realised that retaining walls have a very definite job to do — the supporting of a great volume and weight of soil. Foundations must be adequate, weep-holes provided to permit drainage and an inward-leaning batter to help balance the weight of the soil.
Where the height is not too great (1.25 m [4ft] is about right) retaining walls can be of the uncemented dry-wall type. To do this well is an art indeed but to do it acceptably (if one’s standards are not impossibly high) is well within the capability of any week-end gardener, and it becomes a fascinating ploy. Obtaining natural stone from any distance is extremely expensive: terracing above a rocky subsoil however, frequently produces a considerable proportion of the wherewithal. This should be so used whenever possible.
Much more of a problem is when the site slopes upwards to the north from the back of the house. (As this implies a fall from the front, an area around the front door becomes a possible place for a sitting-out area if relative privacy can be contrived: there is no law to say that one must sit out only behind the house.) In such a case light is at a premium. The terrace level should be taken out as far as practicable, but realising that in doing so the retaining wall when it is reached may have to be aggressively high. Better perhaps is having a 2 to 3m wide (6 to 10ft) ‘terrace’ and then constructing a series of shelves like a wide flight of stairs across the full front of the site. This would make a marvellous rock garden with cascading plants falling over each level and facing the windows.
Sloping sites either nearly nullify or exaggerate the size of plants chosen to give privacy or shelter. Planted at the bottom of a sloping garden, trees may have to get to near-maturity (and take a century to do it) before they rise above the line of sight from the top terrace, while conversely relatively small shrubs take on an altogether unwanted importance when planted at or above eye level. Privacy may have to be contrived in small areas and planting, hedging or walling kept very close indeed. Similarly positions of greenhouses and other garden buildings need especial care if they are not to impinge too much upon the scene.
Obviously not all parts of a sloping garden can be terrace: nor indeed is it desirable. Informal planting on sloping ground, so long as it is not precipitous, is always full of interest. Maintenance, however, can be difficult and where space permits trees and shrubs under-planted with bulbs are best in rough grass. Paths or rides can then be mown where necessary. Consideration will need to be given to using machines capable of taking the extra effort of uphill work.
Where stone or brick terracing is inappropriate or merely impossibly expensive, the divide between two flat areas has to be a bank. This cannot be satisfactorily secure with a more than 45-degree slope; 30-degree is better but, of course, uses more space. Again there are problems of maintenance: grassed banks can look lovely but to be reasonable in an age when spare time seems always to be at a premium first class lawn quality is best replaced by use of the invaluable air-cushioned mower. Set it low and it can do a marvellous job and high banks can be dealt with by letting it down on a rope (vital, also, for safety, if toes are to be cared for).
Alternatively, many ground-cover plants provide trouble-free bank cover and often flower as well. Hypericum calycinum and Cotoneaster microphylla are good examples and there are several superb horizontal-growing junipers which seem made for this job.
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