Preparing the Soil for Hardy Perennials: If plants are expected to grow well in one position for several years, as is the case with hardy perennials, it is only common sense to prepare the planting site well. It is a common mistake to think that because many of them are easy-going, almost anything will do. There is a big difference, however, between merely existing, as they will in poor soil and flourishing, as they will if trouble is taken to enrich the ground.
A good soil structure, brought about by digging the top 9 in and breaking up the bottom 9 in with a fork, at the same time generously working in manure, compost, peat or leaf-mould - collectively known as humus - will pay dividends. Roots are encouraged to grow and spread into these materials, and a good root system is essential to create and maintain maximum growth.
It is hardly possible in practical terms to overdo this initial ground treatment. On light, hungry soils, it gives body, weight and moisture-holding properties. And on heavy soils, exactly the same materials and treatment prevent it settling into a solid mass that roots can hardly penetrate.
This added humus may in itself contain very little actual plant food. Different materials possess varied amounts of nutrients. Peat, for instance, has none at all, while good farmyard manure may be very rich. Their main function, however, is as a ground conditioner. Humus, whatever it is, will give soil a good structure, and that is of primary importance.
The classic way of adding the nutrients for long-standing subjects is to dig in at planting time a slow-acting fertilizer. Bonemeal or hoof and horn mixture at 4-6 oz per square yard (110-170 g per m2), mixed in 'with the top spit, will go on releasing food all through the vital first year after planting, and both are suitable for all kinds of plants.
These principles of ground preparation are the same whether for a long herbaceous border, small group of plants or just on single plant. But in the last instance, do not merely dig out small hole big enough to take the roots and no more. On heavy clay soils this can be a death-trap where the plant will drown fro water standing there as if in sump. The minimum preparation for any one plant shoal be 18 in square, with double that size for bigger plants.
The ideal is to get this preparation done well in advance o planting, giving the ground time to settle naturally. A large border would be best dug in the autumn for spring planting, or dug in the spring for autumn planting, using the interval to plan where the different subjects are going, and marking the exact spots with canes. The same applies to a single plant, although if absolutely necessary, preparation and planting can be done at the same time provided the ground is broken up well and the plants well firmed in.
