Soil Types for Growing Roses
Soils vary considerably in composition from one part of the country to another; indeed, different types may exist within the compass of a single garden. If you are an inexperienced gardener, or are about to take over a new garden, you would be well advised to have theanalysed. This can be done by sending samples to a horticultural establishment or, possibly, to your local authority. Alternatively, you can buy a reasonably priced soil-testing kit to determine whether your soil is acid or alkaline.
Roses are reputed to prefer soil that is slightly acid, with a pH of about 6.5. I am inclined to believe thatin general are fairly tolerant in this respect and that it is more important for the soil to be of a good structure and well supplied with organic matter.
For our purposes, soils can be roughly classified as follows:
Clay soils are both heavy to dig and difficult to cultivate. They are made up of particles so small that water cannot readily pass through them, so that they readily becomein wet winters. As a result, clay soils are cold and sticky in the spring and are slow to warm up. Little air can get between the particles, and this means that oxygen will be lacking to help in the process whereby organic matter is broken down to form humus. Summer brings further problems: as clay soils dry out, they shrink; this leads to the development of cracks, which encourage further drying and damage to roots, especially in periods of drought.
The structure of clay soils can be improved by inducing the small particles to form into larger crumbs, a process called flocculation. Some gardeners are tempted to hasten this process by the application of hydrated lime not only to the top spit but to the subsoil as well. Such temptation should be firmly resisted unless analysis has shown the soil to be very acid; lime increases the alkalinity of the soil. Much more suitable is gypsum, which may be forked into the soil at up to 1.5 kg/m2 (3 lb/sq yd). The digging in of organic matter, such as partly decayed leaves and strawy manure, in autumn and winter will also considerably improve the texture. These materials, however desirable, are not always readily available, or are in too short supply to fork into the lower spit.
In this case any material such as old newspapers or worn out clothing (if of natural materials) is suitable and will help to open up heavy clay and improve.
Clay soils retain plant foods better than those oflighter texture and are not so subject to leaching (the draining away of nutrients through the soil) in wet winters. Particularly intractable soils can be improved by dressings of rough sedge peat, which should be broken up and well soaked, and of sharp sand.
Chalk soils, particularly characteristic of downland, are generally not favoured by prospective rose growers. Such soils are often shallow and drain too freely. In addition they are very deficient in organic matter, so that large quantities of humus-forming material must be worked in when preparing the site. Dedicated rosarians, however, are prepared to accept a challenge, and some have done so with considerable success by excavating much of the chalk with a pick, and replacing it with good topsoil enriched with peat or leaf mould. In general, hybrid tea roses do not thrive on chalk, although quite a few rose species and their hybrids will do so. Pemberton roses and many old garden types, such as hybrid perpetuals, albas, centifolias, and damasks, have proved capable of satisfactory growth in chalk soils. Many climbers and ramblers have also been grown successfully, although rugosas, usually so trouble free even in comparatively poor soils, are apt to suffer from iron deficiency in chalk. This shows up as a yellowing of the leaves, known as chlorosis, which can be overcome by dosing with proprietary sequestered iron compounds.
In terms of digging and cultivation, sandy soils are the opposite of clay, and are also quite different in composition. Their particles, being coarse, do not stick together, and so waterthrough them more rapidly — indeed, wastefully so in summer. To counteract this and to help prevent wastage of soluble plant foods, sandy soils should be treated, if at all possible, with heavier types of farmyard manure, from cows or pigs, preferably well rotted. Such material is usually scarce outside country areas and you may have to make do with compost made from garden and kitchen waste.
An alternative product is dried compost from sewage sludge and dustbin refuse; this is obtainable from some local authorities, and it is most useful if used in quantity. These latter composts have many advantages as they are free of pests and diseases and contain some essential plant foods. They are generally low in potash, but if pepped up with sulphate of potash they are excellent for roses. In some industrial areas composts from sludge may contain chemicals dangerous to plant life, so you should make sure that any that you wish to acquire is not polluted in this way. In some areas, spent mushroom manure is advertised for sale. This is also beneficial except where, as is quite common, its lime content is very high. In such cases I would not advocate its use on roses.
Excellent roses are grown by many people on light sandy soils, more successfully where plenty of manure or compost has been forked into the subsoil. In very wet winters excessive drainage can be aggravated by autumn cultivation, so if possible it is a good idea to delay cultivation until the spring.
Although they are high in organic matter, many peat soils are confined to low-lying areas which are so badly drained that they are unsuitable for growing roses. Good drainage is essential; roses object to their roots being kept permanently saturated. High moorland also frequently consists of peat, and again because of bad drainage, as well as of exposure, it too is of little value. Some peat soil is also very acid. I have already mentioned that roses, in my view, are reasonably tolerant so that they can be grown even on fairly acid soils. The addition of lime, especially in the form of ground chalk, will counteract excessive acidity if used at the rate of about 60 g/m2 (2 oz/sq yd).
There can be little doubt that the type of soil generally called loam, in which the clay and sand particles are well balanced, is what most rose growers consider to be ideal. Blessed with such a soil and a high proportion of organic matter, fertility is assured. Most loans have enough body to resist leaching, and beneficial bacteria are more active.
This type of soil is composed of very fine particles which are inclined to run together and become sticky when wet. After rain, compaction takes place on the surface, forming a hard cement-like crust. This makes cultivation such as hoeing difficult, and any cultivation required is best carried out before the surface has completely dried out. Working in a surface dressing of peat or some humus-forming material, especially if allied to mulching, will counteract surface compaction and will generally benefit the plants.