Roses, shrubs, and trees can be grown well in almost any soil, but most soils will be improved by treatment of some sort before planting. The most important part of any preparation is digging.

Trenching

Some gardeners advocate trenching to a depth of two feet or even more, and others say that simple digging to a depth of eight to ten inches is sufficient. Good and bad results are obtained by both advocates. Those who succeed with shallow preparation are usually working on a loamy soil with good natural drainage, due to an underlying layer of readily permeable gravel. Very light soils or heavy retentive soils need deeper preparation. Trenching of heavy soil without installation of an adequate drainage system will be harmful to any horticultural venture. Trenching of light soil allows the placing of a moisture-retaining layer, or water trap, twelve to twenty-four inches from the surface. This can be of clay or heavy loam. It has become conventional to recommend clay for this layer or even as a small patch under each rose. Heavy loam is better; after all, it contains about sixty per cent of clay.

Those who favour trenching say that rose roots penetrate two feet or more in depth. Those who are content with shallow cultivation are just as confident that the roots spread laterally, making deep preparation a waste of time. Both contentions are perfectly sound. Roots will penetrate only as deep as a soil suits them; trenching increases this depth.

A deep soil is a more capacious reservoir for water and plant food than shallow, lightly dug soil. In trenching, the natural drainage of the soil must not be upset, the relative positions of topsoil and subsoil must not be reversed, and large air pockets must be avoided.

Trenching is best done in late summer or early autumn, when the soil is fairly dry. Digging clay when it is wet may do more harm than good. If a trench be filled or partly filled with rough lumps of wet clay it may take months or even years for them to break down; meanwhile there are many air pockets. On the other hand, if wet clay be puddled, especially near drainage pipes, it is rendered almost impervious to water and all drainage systems are rendered useless.

A garden will be better if the whole area is trenched. This makes for better drainage and obviates the danger of each bed becoming more or less a pit in which water stagnates. Trenching is really an elaboration of thorough digging: the aim is to turn and loosen the surface soil and either drain the subsoil or construct a retentive layer about two feet from the surface.

To commence trenching, choose a strip of land three feet wide and the full length of the width of the area to be trenched. Dig from this strip and remove by barrow all the topsoil, leaving the subsoil. If there is enough topsoil take out twelve to eighteen inches of it. In light loams or sandy soils take out two feet of it. This soil should be heaped where the trenching is to finish. Since drainage should have been attended to before the actual trenching is commenced, there is no need actually to remove any of the clay subsoil. If the surface soil is in only a thin layer it is advisable to dig the subsoil to a depth of six to eight inches and at the same time mix into it a little of the surface soil. This will make the clay less dense but drainage will be essential if this is done. The subsoil must remain as subsoil, and should never be mixed with tht upper layers, except perhaps in very small proportions.

Then take another trench three feet wide from the line of the first trench and turn the topsoil of the second trench on top of the subsoil of the other. This will leave the surface level considerably higher than it was originally. Small air pockets will have caused this, and are very helpful in increasing soil fertility provided the soil soon settles and obliterates them. Continue thus to the end of the plot and then use the topsoil that was first removed to fill in the last trench.

Deep sandy soils should always be trenched. A layer of retentive soil, such as clay, or better still, heavy loam, at least six inches thick, should be inserted at a depth of two feet. The soil superficial to this should be well mixed with heavy surface loam, and compost or cow manure. Near the sea-coast, washed seaweed is handy and may be freely used, together with weeds and vegetable refuse. They should not be buried deeper than one foot.

The artificial subsoil steadies percolation, and so maintains a more even degree of soil moisture and temperature. It will save a lot of plant food from leaching away. Costs of water and manures will be greatly reduced by this initial expense and work. Sometimes light sandy soil deceptively rests upon a dense impermeable clay; this will need artificial drainage.

The best soil for rose-growing is a loam that is rather heavy but sufficiently friable to render it capable of being worked into a fine tilth. If it sets hard when dry, and is greasy when wet, add gypsum, dolomite, or a little lime and some organic matter. Otherwise it will not only be hard to work, but it will be unproductive, for its physical structure is unsuitable for root-growth. Use half a pound to one pound of gypsum, dolomite, or lime to the square yard. Over-liming can be very harmful.

If this good soil rests on stiff retentive clay either do not trench at all or be quite certain that the drainage is efficient. It is better to have shallow cultivation than pits in which stagnant soil-moisture gathers, for then conditions that are toxic to plant life will develop. A good drainage scheme accompanied by trenching will greatly improve the physical condition and general fertility of the soil. The depth of good soil will be increased as well as the amount of available plant food and moisture. Good soil aeration will be ensured. The digging of a deep hole for planting each rose in such a soil is equivalent to trenching without draining.

Should there be little or no surface soil overlaying heavy clay subsoil, a good workable layer must be created at least one foot deep. Remove any surface soil present and heap it on one side. Remove the next six inches, the upper part of the subsoil, and heap it elsewhere. Remove the next six inches and cart it away. Obtain some good light to medium loam and stir some into the soil deep to that already removed. Mix a goodly proportion of it with the subsoil that has been saved and place the mixture back in the bed. Some bonemeal, compost, or vegetable matter could be added with advantage. Next replace the old surface soil. If the bed is not high enough add more loam to the top. Dig well several times after completion. These beds will always need good drainage, but will grow excellent roses. They probably entail even more work and expense in preparation than those in very light sand, but they give better results.

The Addition Of Soils And Manures

The surface layers of any heavy soil will be improved by the addition of some light to medium loam. Cultivation of the subsoil is useless unless something is added to it to improve its texture. Experiments show that beneficial results follow during the year after deep stirring, but that the soil returns to its original condition in two or three years unless loam or organic matter is incorporated in it. After roses have been planted the opportunity for improving the subsoil does not occur again. It is better to lose one season with thorough preparation than plant in unsuitable land, badly cultivated because of haste.

Some new compounds, called soil conditioners, will help greatly in breaking down heavy soils that have only a very thin layer of topsoil. They are expensive but, actually, less costly, more effective, and longer lasting than elaborate methods of trenching. They must be mixed with the soil thoroughly and drainage will be needed still.

Moisture containing soil-derived plant food is absorbed in very dilute solution by root hairs, which form just behind the growing point of the root. They are short-lived, but while the root is actively growing they are being constantly replaced. If root-growth is checked they cease to form, and so the supply of moisture and food absorbed by that root is cut off. Should a growing root reach an air pocket its development is checked immediately. In very loose soil this may happen simultaneously to many roots; then the plant dies. If only one root is affected, Nature comes to the rescue and a root is sent in another direction. Plant energy is expended in its production, time is lost, and the whole plant receives a check.

For the foregoing reasons it is very important that all deep cultivation should be completed some weeks before planting. Then the soil has time to settle slowly but firmly, often with the help of rain. When time does not permit this, watering and rolling of the soil must be substituted, but it should be done only if in a great hurry.

Full of air pockets, freshly cultivated soil will soon sink several inches, and in an uneven manner. When fresh organic matter, vegetable or animal, has been worked into it, the shrinkage will be increased as the material rots. Planting should never be done before the soil has settled, for there is risk of the subsidence damaging the roots. Subsidence will be less with added compost, cow manure, blood-and-bone, or fine bone-meal than with looser material, such as stable manure and unrotted vegetation.

Fine bone-meal can be added in any soil preparation with advantage to the intended plants and without interfering in any way with the work. It adds, in even distribution, an organic substance that will feed the plants for many years. Small quantities of other manures are sometimes dug into the upper eight or ten inches of soil after the major part of the preparation has been completed, but this usually does more harm than good by making the soil too rich for the new roses that are to be planted later, unless it is done at least four months before the planting is due to be done, in which case it would be helpful.

Frequent diggings keep down weeds, help in settling and levelling, establish aeration, mix evenly the constituent soils, and produce an upper layer of good friable soil.

Never add manure within a few weeks of planting time; slow-rotting matter will need several months; cow manure should be allowed at least six weeks, blood-and-bone at least a month, and fine bone-meal at least three weeks. They should all be used sparingly. Water will take food down to the deeper roots.

All these instructions may appear very formidable, but they cover all types of soils. Most soils are of the more easily prepared types. Beds need no more preparation for roses than for any other plants much less than for some. In most areas it has become customary to have the level of flower-beds above that of lawns and paths. In very sandy parts they can well be lowered. Perth gardeners often have bed surfaces as much as six inches below their lawn levels, which prevents water from running off them.

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