Organic Gardening

In colder conditions, like those which affected much of the world during the last Ice Age, rocks are broken down by the action of water entering cracks in the rock and freezing. As it freezes, the water expands, forcing the rock to split open. The movement of giant glaciers was responsible for the formation of soil, as it wore away fragments of the rock below, and the action of streams and rivers also serves to wear away rocks to form soil.

The soil in your garden is a very complex structure and its cultivation depends on many different elements. There are several different soil types which all have advantages and disadvantages. For example, the soil may be acid or alkaline; it may be heavy or light; it may drain well or badly; it may be very stony.

What you see in your garden is simply the surface of the soil. Soil is made up of three layers: topsoil, subsoil and the soil parent matter. Top-soil is formed over the years by the addition of organic matter that follows the decomposition of dead plants or animals. It is inhabited by a wide range of living organisms, and it is in this layer that the majority of the feeding roots of plants exist. Topsoils can be improved and deepened by the regular addition of organic matter.

The second layer is the subsoil, which is low in nutrients, generally contains few or no microorganisms, and is therefore inhospitable to roots. Thus, when digging deeply, it is advisable to bring to the surface only very small amounts of subsoil; these can be mixed with organic matter and will, eventually, turn into topsoil. Double digging breaks up subsoil, and improves drainage, without bringing the subsoil to the surface.

The nature of the subsoil has a profound effect on the water-holding capacity of the soil in general. If you have very sandy or rocky subsoil, which drains very freely, you will need to increase the bulky organic matter content, and thus the water-holding capacity, of the topsoil. On the other hand, heavy clay subsoil, which drains poorly, may necessitate the installation of an artificial drainage system.

The third layer - the parent material - is the original mineral from which the soil was formed. This layer is normally deep enough not to concern the gardener, but may, on high ground, be comparatively near the surface. If this is the case, try to increase the depth of the topsoil by adding organic matter to the top layer.