Soil Quality and Soil Testing
Soils and manures
More than any other factor, the quality of your soil will determine how successful you are in growing fruit and vegetables.
Fortunately, practically every type of land can be made to yield good crops. But to make the most of your garden you should first understand the nature of the soil you are dealing with.
Getting to know your soil
Soils fall into five general groups — clay, loam, sand, chalk and peat — but only a minority of gardens can be classified so distinctly. Most gardens have a mixture of soils, though often with one type predominating.
This guide will help you to identify your soil and cultivate it to the best advantage. Use it in conjunction with local knowledge gathered over the years by neighbours and garden societies.
To make your own classification, note first the reactions of the soil to extreme weather conditions, such as drought or prolonged heavy rain.
If puddles take hours, or even days, to disappear after heavy rain, and the soil bakes rock hard in a drought, you have a clay soil.
If water drains away fairly quickly after heavy rain but the ground stays unworkable for a day or two, you have a loam soil.
When water from even a heavy thunder shower drains away within minutes, your soil is probably light and sandy. In a drought, such soil must be constantly watered or heavily mulched.
However, if speedy drainage is combined with a surface that appears dusty white or grey during a drought, you have a chalky soil.
As well as classifying the soil in your garden, you should learn when to cultivate it and when to leave it alone. Cultivation on clay soil, in particular, needs careful timing.
Where a choice is possible, grow the crops best suited to your soil, and within any particular crop select the most suitable varieties. Grow long carrots, for example, on a light soil and stump-rooted varieties on heavy soil. Grow scab-resistant potatoes on chalk soil.
Bear in mind that whatever the type of soil in your garden, you will get out of it only as much as you put into it.
Heavy or clay soils
Soils of this type are the hardest to work because they are difficult to dig at any time and impossible to cultivate during rainy spells. Their growing season is shortened because spring sowing and planting must be delayed until the wet soil becomes warmer and drier.
However, clays have the advantages in summer of not drying out as quickly as sandy soils and, when well cultivated, they yield heavy crops of good quality.
On poorly cultivated land the exceedingly fine particles of clay —which are at least 1,000 times smaller than those of sand — clog together into a sticky mass when wet, and set hard when dry.
In these conditions roots have difficulty in extracting the mineral nutrients on which plants feed. However, clay contains these minerals in abundance and you can make them available to plants by improving the soil texture.
This can be achieved in two ways — by using bulky manures and by digging in the autumn with the aim of breaking down the soil by frost action. If the clay is acid, dressings of carbonate of lime also help in making the soil workable. This should not be applied, however, on the type of alkaline soil known as chalky boulder clay.
Every autumn or early winter dig in all available organic material, such as garden compost, well-rotted manure, leafmould or peat. As this continues to decay it opens up the texture of the soil and gives the roots a freer run. Weathered boiler ash and coarse sand also help.
When digging in autumn, leave large clods on the surface to be broken up by the action of frost. As the ground dries in spring — it should then look light brown — rake the surface to give a tilth fine enough for sowing seeds.
Every third year, after digging is completed, spread carbonate of lime on the surface at the rate of 8 oz per square yard (250g per square metre). Do not work it into the soil, but allow it to wash in naturally.
If the soil drains so poorly that pools of water remain after the rain, it may be necessary to lay drainage pipes. This is an expensive remedy and it would be better first to see if the problem resolves itself after two or three years’ cultivation.
Well-cultivated heavy soils are excellent for growing beans, brassicas, peas, potatoes (if given plenty of compost or peat) , salad crops, spinach, most soft fruits and many tree fruits.
Medium or loam soils
A balance of clay and sand makes these soils highly fertile and easy to work. They are usually dark and contain plenty of humus.
When moist, they feel neither gritty nor sticky. They break down to a good tilth when dry but they become lumpy if worked too soon after rain.
All types of vegetables and fruits can be grown on loam.
Light or sandy soils
These soils are easy to work and they warm up quickly in spring, so making them valuable for growing early crops.
They are so porous, however, that soluble plant foods are constantly leached, or washed out of them. This leaching can be reduced by digging in garden compost or well-rotted manure. The humus formed also acts as a sponge to retain moisture.
To reduce loss from leaching, add compost or manure in late winter or early spring rather than digging it in before the main winter rains or snow have fallen.
Many crops on light soils have to be watered in summer, but you can reduce the frequency of watering by spreading a mulch of peat at least 3in (75 mm) deep along the rows of plants.
Alternatively, crops can be mulched with spent hops, wood shavings, straw, bracken or black polythene. Always soak the ground well before laying the mulch. Before digging in wood shavings or straw, sprinkle on sulphate of ammonia at the rate of 2 oz per square yard (60g per square metre).
Plants on sandy soils respond readily to general fertilisers. Give several small applications over the growing period rather than one heavy dressing.
Sandy soils are often deficient in potash, so supplement a general fertiliser by adding sulphate of potash at the rate of 1 oz per square yard (30g per square metre) , or use a tomato fertiliser, which has a high potash content.
Root crops, potatoes, onions, early cloche crops, outdoor tomatoes, asparagus and some of the less hardy tree fruits, such as peaches and apricots, can be grown successfully on well-cultivated light soils.
However, certain types of vegetables vary in their response to light soils: French beans, for example, generally crop better than runner beans, and New Zealand spinach better than summer spinach.
A thin layer of topsoil usually lies on chalk or limestone subsoils. Sometimes, as in parts of Kent and Sussex, the chalk is apparent in the greyish topsoil. The chalk will stick to your shoes in wet weather, but the surface seldom remains wet for more than a few hours.
These soils are strongly alkaline and seldom need liming. The main need is for organic manures.
Every autumn or early winter dig in all available garden compost or well-rotted manures. Peat, reinforced with dried poultry manure or fertilisers, can be used as an effective, if expensive, substitute.
In spring give a dressing of sulphate of ammonia or nitrate of soda at the rate of 2 oz per square yard (60g per square metre) to overwintered crops such as spring cabbages and sprouting broccoli. These crops often look pale and sickly after a wet winter on chalk soils, but a nitrogenous fertiliser soon restores their colour and vigour.
Chalk soils dry out so quickly that in some seasons watering and mulching may be necessary as early as May, or even April. Even so, well-established plants will show drought symptoms later than on a sandy soil, and early application of a mulch will ensure continued growth in all but the driest conditions.
Beds of black currants, raspberries and strawberries should, however, have a permanent mulch of peat or garden compost to a depth of 2-3in (50-75 mm ).
When well cultivated, this type of soil suits most vegetables except potatoes, which tend to do better in slightly acid conditions. To create more acidity, cover each tuber with a double handful of peat when planting.
Stone fruits, especially plums and gages, do well on chalk soils, but keep newly planted trees well watered during dry spells for the first year after planting.
These are the least common garden soils. There are two completely different types: fen peats, which are probably the richest and most productive of all soils; and acid peats, which are sour, often waterlogged and extremely difficult to make productive.
The acid peats are found on and around moorland where decaying vegetation has accumulated over wet or impervious subsoil, or rock. They are acutely short of lime, and of essential nutrients.
Some form of drainage may be needed to bring them under cultivation. Every autumn, dress with carbonate of lime at the rate of 8 oz per square yard (250g per square metre).
Use a general fertiliser at the rate of 2 oz per square yard (60g per square metre) during the growing season. Until the land improves, concentrate on crops known to do well on acid or neutral soils, such as blueberries and potatoes.
Fen soils, on the other hand, are easy to work and almost any crop will thrive in them.
Making a new garden or reviving an old one
Anybody who moves house must expect some surprises and a few problems when taking over the new garden.
The biggest gamble comes when moving into a newly built house, where the builder may have left the garden strewn with rubble and subsoil, or into an old town house where the soil is exhausted.
When getting a house built, arrange with the builder as early as possible for topsoil removed from foundation trenches to be placed in a mound and subsoil to be removed. Later, when creating the garden, spread the topsoil on the vegetable plot.
If you take over a new house which has already been completed, it may be necessary to make random trial diggings to determine the depth of topsoil and to see whether subsoil has been left on the surface.
If it is impossible to put things right by harrowing soil from one part of the garden to another, buy in a load of topsoil to provide an adequate depth for growing crops. A lawn may grow on a fairly shallow soil, but you will have little success with vegetables or fruit unless there is a minimum of 8-10 in. (200-255 mm) of topsoil.
In the first few years dig as much rotted manure as possible into the vegetable plot. In the first season turn a large part over to potatoes, which by constant cultivation will help to clear the ground of weeds. Grow peas and beans, too, which add nitrogen to the soil, and quick-growing salad plants.
Thereafter, follow a rotational cropping plan.
The soil in the neglected garden of an old town house is generally sour, with a high sulphur content. This is because rain brought down large amounts of sulphur in the time of open coal fires and belching factory chimneys.
It is better to treat such ground as subsoil rather than try to put new life into it. Dig it over and add manure or compost, lime and fertiliser dressings to improve fertility. Alternatively, spread a deep layer of good topsoil over the surface.
Since topsoil is expensive, treat a small part of the garden at a time rather than spreading the soil thinly over a larger area.