What most new gardeners fail to appreciate is that the actual quantity of food taken by a plant from the soil (apart from water, which is considerable) is very small, and that in soil which contains humus the essential foods are generally present. Plants rarely need half the fertilizers that ambitious amateurs shower on the beds and borders. What they do need is soil in the right mechanical or physical condition to hold the essential foods in readiness for the roots when they need them. In other words, “tillage is manure” in its best form.
Even without digging a hole, the condition of the soil can be noted, especially if the weather is wet. Clay soil sticks to the shoes, while sandy soil does not cling much. In dry weather, sticky clay cracks badly, while sandy soil becomes powdery, and shifts under the feet. There are other differences, one being in the type of weeds that grow on the site; but unless the gardener is a botanist or an experienced countryman it is not likely that a description of these will be of much assistance to him in determining his particular type of soil.
It must not be thought that every soil falls clearly into one of these two categories. There are intermediate types, and the ideal loam (existing where a garden has previously been under good cultivation) is about half-way between the two. But there are also other distinctions between soils of different districts. There is, for instance, the type of soil generally called chalky, where the soil lies over a subsoil of chalk or limestone, which is brought to the surface in small or large quantities whenever digging is done. Such soils are generally “hungry,” that is, they have little food left in them, because plant food in solution can so quickly find its way through the limestone. The thinner the layer of dark soil over the chalk or limestone, the poorer it will be.
Then there is the soil known as peaty—the type that is found on moorland and bog. Bog peat is sour and unfriendly, but peat that is lying in such a position that it does not become constantly waterlogged, such as the peat of the moors, is valuable garden soil, and particularly suited to certain plant families.
Alluvial soil or soil from river beds is another type—the richest and best type of all for garden making. Alluvial soil occurs all over the country, wherever old river beds have dried or been drained artificially. The reason for its fertility is that decaying organic matter has for many centuries been carried down stream, and gradually deposited in the river bed. This, combined with the breaking down of rock particles by the action of moving water, has produced a rich loam that holds plant food without waste (such as occurs on chalk) and that is comparatively easy to work.
Marl—the kind of soil which occurs in some of the midland counties—is really clay soil, but clay that contains a good deal of chalk or magnesium carbonate. It is in better condition for gardeners than simple clay, easier to work, and generally fertile.
Having noted the kind of soil that is available for you to use in making the garden, you might note also at this stage whether serious water-logging is likely to occur on the site. In the foot-deep holes that you made in order to sample the soil, water will doubtless collect during rainy weather, especially if the soil is of the clay type. You can expect this, but you should also expect to find the water disappear from the hole after two or three days of dry weather. If it still remains, there is need for special drainage, and neglect on this point will lead to damp, sinking lawns, and unhealthy borders.
To drain a garden it is generally quite enough to take out a trench about 18 in. deep every 5 or 6 yards, and put 9 in. of coarse breeze or clinker, cinders from the house, or old tins, beaten flat, into the bottom. The soil can then be returned to the trench. This is a wise precaution on every garden where the soil is really sticky clay and where a lawn is to be made. The borders, being more deeply cultivated, will take care of themselves unless the drainage is unusually bad.
If more thorough drainage is necessary, a 2-in. or 3-in. pipe can be laid in the bottom of the trench. Agricultural pipes are in 1-ft. lengths, and should be laid with their ends touching. In either type of drainage, the whole system should lead to a sump in the lowest part of the garden, unless the garden is surrounded by a ditch. A sump is a hole partly filled with broken bricks, rubble, and so on, and re-covered with soil. Where pipes pass under a path, they should be supported by a creosoted wooden rail, or they may break under the weight of a heavy barrow.
Just in case any gardener feels, after reading these lines, that he is up against a stiff proposition, let me assure him of the very definite advantages that his soil will give him—whatever its type. If it is heavy soil, it will retain moisture better in hot weather, will retain plant food better at all seasons, and will therefore prove more fertile. It will grow roses and fruits to perfection, and make an excellent vegetable plot when it gets going.
If it is light soil, it will be very easy to turn frequently, and delightful for seed raising, for flower growing and for many of the most charming flowering shrubs. It will make a good winter garden, since light soil is generally warmer than clay; and crops of the vegetable plot, if not quite so heavy, will be much earlier than those on clay soils. In fact, every soil has its advantages.
To a great extent, the work done on the garden site is similar whatever the kind of soil, but it would be a mistake to begin without some appreciation of the soil type, and in outlining the methods to be adopted, constant reference will be made to the two extreme types. But whatever the soil, the first task is to dig it thoroughly.
HOW VIRGIN SOIL IS TREATED
Virgin soil, the kind of soil that has been idle for a year or two since it was bought for the garden enclosure, is generally old pasture land, or is covered with a kind of weedy pasture that has grown up during its idleness. A great many garden owners think that the right way to tackle this virgin soil is to take off the existing turf and burn it, but this is a great mistake. The argument used by old-fashioned gardeners is that wireworms are present in old turf, and that weed seeds will be destroyed by the burning. Actually the wireworms are as likely to be present in the soil just under the turf as in the turf itself, and weed seeds will probably in any case fall into the under layer as the turf is lifted. On the other hand, the turf and weeds, if buried under the top soil during digging, will gradually decay and form humus, which will add considerably to the soil fertility.
PREPARED AND HOME-MADE FUMIGANTS
Should it be desired to crop the garden with various vegetables the first season, it would be as well to use soil fumigant while preparing it. Soil fumigants are sold in prepared form. They consist of naphthalene with other ingredients, and this material when dug into the soil so that it lies below the top spit (spade-depth of earth) sends its fumes through the soil, and insect pests are gassed as they hatch from the eggs. It is obviously waste of fumigant to use it, as some beginners have done, as a top dressing, for the fumes then merely rise into the air.
A home-made fumigant consists of half naphthalene and half powdered lime, mixed and used at the rate of one or two ounces to each yard of open trench during digging. Horticultural naphthalene should be specified when ordering this material.
It has already been stated that soils in good mechanical condition, i.e., broken to a crumbly texture, so that air and moisture can both find their way through and be constantly available to plant roots are generally well enough supplied with plant food. This does not mean that all soil is equally fertile, nor that soil will grow any and every crop without ever needing additions of any kind. Soil fertility is apt to deteriorate unless care is taken, and to maintain it one should first understand what soil fertility is and what it implies.
To begin with, consider the plant roots and their requirements. They need two things—air and moisture; without air they begin to decay instead of carrying on their proper function and without moisture the plant will die, since plant food can only be taken in by the roots in solution. Air and moisture depend on the ability of the soil to hold moisture during dry spells, and to allow for quick drainage of surplus moisture (and the inlet of air) during rainy spells.
BACTERIA AND SOIL FERTILITY
It has been found that an intermediate soil or loam, partly clay and partly sand, is best in this respect. It is also found, by practical experience, that soil rich in humus will retain moisture longer than a poor soil, and that well-broken soil, that is soil that has been dug over to a depth of nearly 2 ft., holds air and moisture better than soil that is never turned over. Further, it is found that soil dug over in early winter is better in this respect than soil turned over in late spring just before the crops are sown and planted.
The reasons for the greater fertility of soil dug in early winter have only been appreciated with increased knowledge of soil bacteria. These bacteria are living organisms, and depend for their health on congenial soil conditions, such as exist in well dug soil. If the soil is newly turned in early winter, the bacteria are active below the surface all winter, building up a reserve of plant food, and increasing in numbers so that they can be still more active when the growing season commences.
The bacteria are present, not in the gravel or sand which forms the bulk of the soil, but in the decaying humus. This explains why the addition of humus to the soil improves its fertility. Other uses of humus in the soil are that it darkens the colour of the soil, and the darker the soil the more solar heat it conserves, so that humus actually raises the soil temperature; further, in the process of decay, humus ferments, making the soil more porous. That is why humus in clay soils will make them seem lighter. In sandy soils the humus makes the texture heavier by holding moisture.
VALUE OF PLANT FOODS IN THE SOIL
Apart from texture and bacteria, fertility depends on the presence in the soil of plant foods. Of these there are three of supreme importance to the amateur gardener. One is nitrogen, a food that encourages the development of leaf and stem; another is phosphorus, which hastens flower production (and therefore fruit production); and another is potash, which is a kind of tonic and maintains the health of the plant. For most plants lime is also an essential, but there are certain plants that grow naturally in lime-free soils.
Lime in itself should not be regarded as a food. Its function is to prepare the other foods for the plants, to break down lumps of clay and make sandy soil more retentive of moisture, and in various ways to assist the plants to take their food supplies from the soil. It is often spoken of as the key to the soil, while the three plant foods—nitrates, phosphates and potash—are spoken of as the golden tripod.
In addition to these there are a number of other chemicals of which minute quantities are absorbed by the plants, and, in fact, chemists are constantly discovering that microscopic quantities of certain substances are absolutely essential to plant health. As, however, these substances are usually present in all well dug and manured soils, there is no need for the amateur gardener to consider them.
Appreciation of the various functions of the three classes of soil food helps the gardener to control his plants. It helps him in another way, too. As has been said, nitrates (substances containing nitrogen) are responsible for the development of leaf and stem. They are specially called for by such plants as lettuces and cabbages, and it is pretty obvious that after cabbages have been grown on a plot of land for one season, the soil will be less rich in nitrates than before.
The same sort of thing happens with the other plant foods. Certain plants take more than others, and the gardener’s task in keeping up the standard of fertility is simplified if he remembers these points. After a cabbage crop, for instance, he will either need to use more nitrogenous fertilizer for the next crop, or he must change over to a crop that does not need so much nitrogen, but requires more potash or more phosphates. This principle of changing over the crops is generally called “rotation of crops.”
It will be gathered from all these remarks concerning plant nourishment, that the methods of increasing and maintaining soil fertility are these :
1. Regular digging, forking, hoeing, etc. so as to aerate the soil.
2. Keeping up the supply of humus in the soil.
3. Restoring the essential plant foods when soil has been impoverished by cropping.
5. Using of lime where necessary.
The word manure is synonymous in the mind of many an amateur gardener with stable or farmyard manure. The reason is that stable manure is so generally effective that when it was available in quantities, every gardener used it and found it good. Stable manure contains a little of each of the three plant foods, and in addition it improves the texture of both heavy and light soils.
Where animal manure of any kind is available, it should be either dug immediately into the ground, being mixed with soil of the top spit (if used in early winter), or buried in the lower part of the top spit of dry sandy soil (in early spring), or distributed on the soil surface in late spring, after planting is complete, where it helps to conserve moisture. Animal manure should never be stacked in the open without a soil covering, partly because it is offensive, but more because it loses half its value when exposed to air and rains.