Hardy perennials are no longer a neglected subject in the gardening scene. The time is happily past when they were relegated in so many gardens because the rewards they gave were disproportionate to the trouble entailed. The conventional herbaceous border was largely at fault because of its long narrow shape with a backing wall, hedge or fence. The plants it contained suffered from overcrowding, weakly growth and excessive competition for light and air. Quite often such borders were too narrow in relation to the height of the plants they contained. All this accentuated the main disabilities to which perennials are prone if not given a fair chance — difficulty of access to a border and the need for supports.
The factor of adaptability must be reckoned with. The majority of kinds grown and offered by nurseries are adaptable to ordinary garden conditions, but it would be as much a mistake to plant something which is by nature shade or moisture loving into a dry open situation as it would the other way round. It would also be a mistake to plant as neighbours something rank or invasive with what is by nature of slow or lowly growth. The need then is to have some foreknowledge of the habits of what one wishes to grow and to avoid indiscriminate planting.
The principle to apply is that of making a selection of plants best suited to the place in which they are to grow. The range of subjects existing in gardens and nurseries is sufficiently wide for this to be achieved, no matter how small the garden, or unkind the soil, so long as it is not completely hemmed in by tall buildings or overhung by large trees to exclude both light and air.
Overcrowding and overhanging by trees or other taller growth inevitably leads toweakness, and plants in close competition for light and air becomes excessively tall and spindly. In the majority of cases where border staking is necessary, it is not the fault of the plants but of the conditions under which they are grown. Light and air are vitally necessary to sturdy growth for all kinds of plants that prefer sunlight, or an open situation as most perennials do.
Bearing in mind the need to make a selection of plants best adapted to the site, the preparation for a bed or border of hardy plants should includeif the soil appears excessively wet or sticky in winter or hard baked in summer. Thorough digging will mostly suffice, since the surface may have been panned down by builders’ vehicles or machines.
Summer and autumn are of course the best times for deep digging on heavy soil, which will enable winter frosts to break down hard lumps and clots into quite fine tilth for spring planting.
On both light poor soils and heavy clays, humus, in the form of peat,or farmyard manure, are recommended. These will improve the texture, as well as the fertility of the soil, and give plants such a good start that nothing but occasional topdressings of fertilizer will be needed for years.
There is no doubt whatever that island beds give the best reward in terms of value for money and effort in maintenance. An island bed can be sited anywhere so long as all-round access is possible, even if it is only a narrow path on one side or end. It is quite feasible to convert a backed border into an island bed so long as there is sufficient width for no matter what the backing consists of, rear access can be provided either by a narrow path of grass or paving used as stepping stones.
If the backing is of a wall, it can be used for climbers and a strip allowed along the foot for bulbs or any of the wide variety of dwarf plants or climbers that like such a spot. The rear part of the bed itself should have, as edging, dwarf early-flowering perennials such as bergenias, pulmonarias, epimediums, for even if the border has a sunny aspect, the taller kinds of perennials facing the adjoining groups will provide for summer shading. This strip at the rear will prove a source of delight in spring and if colour has gone by summer, one has at least easy access to the rest of the bed for maintenance work, and there will be far less staking anyway, because the weakening effect of the backing is greatly lessened.
Only one-sided beds which are on a small scale, where heights of plants grown are in keeping with the effective width of the border, are worthy of consideration. If a garden admits of no compromise, or has no site suitable for an island bed, fair enough, but a one-sided border will inevitably be more troublesome to maintain unless a very careful selection of plants is made.
Whatever type of border one decides to plan and plant, its success and potential interest will depend not only on a well-chosen site, well-prepared soil and the right selection of plants, but on its width. The narrower the bed, the more restrictive one should be on the height of subjects grown. Nothing looks more incongruous than to see plants flowering at 4 or 5 ft. high in a bed only 4 or 5 ft. wide. A safe guide in making a selection of plants is to measure the effective or plantable width of the border in feet, and halve it to arrive at the maximum height of plants it should contain. This would restrict a 4-ft. Wide border to plants of no more than 2 ft. tall, but a little latitude or discretion could be allowed for the very erect spiky plants — such as kniphofias — to exceed the limit.
This is a rule that can apply to any type of border — island or one-sided — bearing in mind that in the former, the tallest are in the centre parts, and at the rear in the latter.
Grouping is another factor worthy of careful consideration. Where space is very restricted and where there is a preference for variety, then a case could be made for having only one plant of each kind — butof subjects or kinds should on the whole be practised from say three of a kind together for a small bed of about 100 sq. ft. in area, to ten or fifteen plants for the largest beds up to a 1000 sq. ft. or more.
The average spacing to be recommended if good quality nursery-grown plants are used is about five to the square yard. If, for example, groups are of five plants of a kind, this gives a planting distance of about 16 in. from plant to plant within a group. But the space around it, up to the outer plants in adjoining groups, should be more, say 20 in. Spacing required depends of course on the spread or robustness of the subject. It can vary all the way from a single plant occupying a square yard in a few cases, to nine plants of some dwarf slow-growing subjects.
If in the process of making a new bed or border, an error in placing occurs, it will show up during the first flowering season and can easily be rectified then.