Basic Soil Types and Soil Drainage

Soil

To the non-gardener earth is just earth. It is when you want to start growing things in it that it begins to take on a rather different character.

Soil is made up of two basic types of material-mineral and organic. The mineral part is the result of vast geological forces that have, with the assistance of weathering over an immense period of time, broken down basic rocks into finer and finer particles. Basically therefore, the type of soil in any garden will depend very largely upon the type of rock from which it has been broken down. The organic part of earth is what is called humus. Humus is the sum of all the decaying vegetable and animal mailer in the soil. What it does is to form within the structure of the soil a kind of sponge which retains water and enables plants to acquire essential nutrients from the soil.

There is a third component of soils that is often forgotten: and that is what is known as the soil population. This is made up of a surprisingly large number of creatures, some of them beneficial, others pestilential, which live in the soil: these include not only the obvious creatures such as earthworms, but also a very large number of micro-organisms. The extent of the soil population will depend largely upon the amount of humus in the soil: it is the function of these micro-organisms to break down dead creatures and vegetation and release the plant nutrients locked up in them so that the plants can use them. Thus the overall fertility of any soil depends upon the ratios in which these various elements are combined.

Soil profile

Image via Wikipedia

Basic Soil Types

Gardeners recognise a number of different types of soil: each has its own peculiar advantages and disadvantages.

LOAM

This is the ideal soil in relation to structure. It feels smooth without being gritty or sticky rubbed in the hand when sampled moist. Neither is it powdery. A light loam has more sand in it — more than two thirds. A heavy loam has more claymore than one third. A medium loam has just the right texture and retains water and food well. It warms up quickly in spring, enabling plants to get away to a good start. If it becomes very acid it will need dressings .of lime, and it is best to add small amounts of lime at regular intervals rather than wait till the soil becomes too acid. Humus-making composts and manures will be needed, as well as fertilisers.

SAND

This is a non-sticky soil even when wet, and those used to heavy soils often envy gardeners with sandy soils because the latter are so easy to dig or hoe. But it is a hungry soil needing a lot of manure, peat, compost, etc. and fertilisers. It warms up quickly in spring for early sowings.

CLAY

A heavy, cold soil, it is sticky to the touch when wet and binds up into unbreakable lumps in dry weather. Improvement of drainage as mentioned below will help it to release the valuable plant foods usually retained in clay. These will also need supplementing with fertilisers. It is usually too acid and more liberal liming will be needed.

CHALK

These soils are rich in lime and so one cannot grow lime-hating plants such as heathers and rhododendrons. The top-soil is often dark and thin exposing a white or light coloured sub-soil of almost pure chalk. The ground seems very wet and sticky after it has rained, rather like clay, but it then dries out rapidly, becoming hard and rough to the touch. It is more easily and profitably dug in this state. There is a great need to improve it with organic humus-making matter including strawy manure, compost, peat, etc., in order to help it retain the moisture better. Avoid deep digging or you will bring up the sub-soil, which is a fatal thing to do. Mulching helps to retain moisture and dressings of lime may become necessary from time to time.

PEAT

Dark, spongy soil often very rich in plant foods; if it is the fen peat type it will need good drainage and lime, as it is invariably too acid. Peat soils should not be over-limed, however, as this upsets the chemical balance of the soil.

STONY

The proverbial infertility of stony ground is due to the fact that all the moisture runs out of it so quickly. However, a few stones in the soil may actually help to retain the moisture. It is, in any case, an almost impossible task to remove all the stones as more seem to surface to take the place of those removed. A far more positive approach is to add plenty of moisture-retaining and rich humus-makers, such as compost, manure, etc. together with plenty of fertilisers.

Soil testing

One of the most important aspects of soil balance which has not so far been considered in great detail in discussing the soil is the acid/alkali ratio. All garden soil is either acid or alkaline and the degree is measured on what is known as the pH scale from 0 to 14. Thus below 6.5 the soil is termed acid and above 7.5 it is alkaline. Some plants like Erica (below 5.5), hydrangea, blue (below 5) and rhododendron (below 4.5) thrive on acid soils; others like brassicas and lilac prefer more alkali in the soil. An acid soil is easily balanced by introducing lime. An alkaline soil with a very high pH is less easily corrected with additions of peat, compost and sulphate of ammonia. The amount of lime needed depends on the type of soil as well as the pH, because some types of soil need more than others to correct acidity.

The simplest way to find out the state of your soil is to get some test papers from a garden shop, mix up a little moist soil with some water in a saucer and leave for about 15 minutes. If your soil is acid give about 1/2 lb. of hydrated (concentrated) lime to sandy or loamy ground per square yard. On clay soil give 3/4 lb. per square yard. More expensive kits will enable you to say more precisely, but the above is sufficient for most gardeners’ needs.

Soil testing kits will help you to find out exactly how much NPK there is in your soil, or you can write to the county horticultural adviser at your county council for his advice.

Drainage

Paradoxical though it may seem at first sight. Plants and people have a lot in common. Both need air and water for survival, but both need them in the right proportions. Thus though everyone would admit that it is necessary to drink water in order to stay alive, the same people would admit that it is not necessary or even desirable to drink all the time, nor would they like to drink stagnant water. Precisely the same applies to plants. They need a soil that is moist, but well-drained. Very few plants can live with their roots perpetually submerged in stagnant water. At the same time, any soil that is waterlogged is also a soil from which air is excluded, and plants need air at the roots to live.

Soils in which these adverse conditions exist are called badly drained soils, and steps must be taken to improve the drainage. Usually good deep digging, will achieve all that is necessary, but sometimes it is necessary to take more drastic steps and introduce drainage pipes. However, if the decision is taken to lay drainage pipes it is one that should be taken before undertaking the next task, so that the two can be done together.

04. September 2011 by admin
Categories: Gardening Techniques, Soil Cultivation | Tags: , , , | Comments Off on Basic Soil Types and Soil Drainage

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