It cannot have escaped your notice as you fight your way through the jungle outside the patio door that under all this herbage is a substance in varying shades of brown, known as Soil. As soil plays a very important part in the growth, healthy or otherwise, of most of the plants you’ll want to grow, it is not a bad plan to learn a little of what it’s all about.
The largest part of soil is made up from particles of mineral rock broken down by the action of air, rain, frost, ice, snow, wind, etc. into varying degrees of fineness. Into this, a plant anchors itself with its roots. Where these mineral particles haven’t been ground down so finely, they are present in the soil in the form of stones. In addition, a fertile soil capable of supporting healthy plant life contains a high proportion of humus. Humus is the remains of dead plants and animals, which are being broken down by bacteria.
Plants require certain major and trace elements in order to survive. The main elements needed are nitrogen, phosphorus and potassium and carbon, hydrogen and oxygen which are obtained from the air. Magnesium is necessary in smaller amounts, and very small quantities of other elements, known as trace elements, such as boron, copper, iron, manganese, molybdenum and zinc, are also required to prevent the plants developing deficiency diseases. These elements are obtained naturally, mainly from the breakdown of plant and animal remains, but also from the gradual dissolving of the mineral rock particles.
Soil also contains a large number of animal organisms, which play their own part in the way that plants obtain their food. Dead plant remains are pulled into the earth by earthworms and similar creatures for their own nourishment, and are thus broken down into other substances. Also, in taking this dead matter into the ground, these so-called macro-organisms bring about its exposure to soil bacteria, which also break it down for their own food, and in doing so they release plant foods. When such creatures die, the nitrogen given off from their bodies is taken up as well by the plants. Soil borne pests are those which live in the soil, but prefer to eat living plant tissue, causing damage and even death to the plants they feed off.
There are also other primitive forms of life to be found in soil, such as fungi, each playing their own part in the never-ending cycle taking place.
The essential elements are made available to plants in the form of soluble salts and other compounds which are dissolved in the moisture contained in the soil, and taken up through the root hairs at the tips of the plant’s roots.
Topsoil is the top layer of soil, which contains most humus and animal organisms, and is therefore the most fertile. It varies in depth from place to place, but is usually about a foot deep. This soil should never be permanently removed as it is that which sustains healthy plant life.
to be continued…