Knowledge About the Soil

When we have enough knowledge about the soil we use the easier our gardening will be. The soil is a unique mixture of assorted ingredients that contains all the nutrients that can sustain life on earth. Plants are so unique that they can extract these nutrients of the soil through their roots and transform them to forms usable by the plant, other animals and by mankind. With this knowledge about the soil, we the gardeners, have the job of keeping soil in the best possible order and to replace the nutrients that the plants have used up.

The soil has five main components: inorganic bits and pieces of rocks and minerals; dead and decaying organic matter, more commonly called humus; air; water; and a prolific community of living things, ranging from earthworms, insects, and fungi to microscopic bacteria, viruses and protozoa. The nature of any soil is usually defined by the proportions and quality of all these components.

The nature of soil varies a great deal, not only from different depths of the same location, but also from place to place. If you dig down three feet or more you will uncover a series of distinct layers, varying in texture, composition and color. If you take all these layers together they make up what is known as the soil profile.

The topsoil, or the upper layer, is usually darker than the layers farther down because it is richer in humus. Life is most abundant in this layer, and it is here that most plants develop the roots that will use up most of the nutrients. Topsoil can be an inch or two deep, or it could be a foot or two. Most often it is usually thinner on steep slopes and much deeper in flatter lowlands. The lowlands are the areas where humus and silt are carried by rainwater runoff. Even though several plants will grow in shallow topsoil, they will also need fertilizing more often and water to flourish in it.

The subsoil layer is under the topsoil. It is much harder to dig and is more sticky when wet because of the high clay content it contains, and most of that is washed down from the topsoil. Also washing down from the topsoil are oxides of iron and other minerals, this often gives the subsoil a reddish or orange color. These minerals can collect at a given depth and it will cement the soil particles into a layer called hardpan, which will often block the penetration of roots and tampers with drainage.

Under the subsoil lies the geologic base this is the mineral matter that is often, but not always, the parent material of the soil above. It might be solid bedrock; or be loose and porous to great depths, no matter what it is the roots of trees and some shrubs will most likely reach well down into it.

Now that we have the knowledge about the soil, we have a better understanding how our plants will survive and what we need to do to replace whatever our plants have taken from the soil in our gardens.