There are few things that all gardens have in common, but they all consist of some sort of soil. Garden soil is very variable. Some of us take gardening seriously and some do not. If you are one of the former, read on. It recently came to my attention that a large percentage of gardeners still refer to soil as ‘dirt.’ Let us have a closer look at its composition. Soil is a living thing, teeming with life. It is this life that makes it possible for us to grow plants.
The life forms present in soil make it a miracle in themselves, and in our gardens they range from stones the size of a potato right down to microscopic bacteria. Everything that makes up a soil is a solid, a liquid or gas.
The largest fraction of a soil is the mineral matter from which it is made, and the nature of this is dependent on the parent material: the clay, rock and sand that underlies it. It is also the type of the parent material that determines a soils texture and type. By nature of this blog we cannot describe in great detail all the aspects of soil types and textures.
With the ‘solid’ phase, we come to the most important part of any soil; the organic matter, without it a soil could be considered dead, because it is in organic matter that all the microbes and other minute forms of life exist.
The organic matter in a soil helps to provide the plant foods that are necessary for healthy plant growth. Organic matter in the soil can be both living and dead. One is the microorganisms and other creatures of various sizes; the other is the vegetation; all the soil fungi and plant roots. All living things are vital in carrying out chemical and physical changes in the soil and they are also important once they have died. It is from the dead remains that plant nutrients are derived in nature.
Moving on to the liquid content of the soil, not surprisingly, this is in the form of water.
Clearly water is vital for the health of all growing plants, but it also has two other important functions. One is that all soil organisms and microorganisms are completely dependent on it for their existence. The other and possibly more important job that water does in the soil is dissolving and transporting nutrients to the plants. Until these have been dissolved in water they are quite useless. Roots only drink; they have no teeth. Water, therefore, is responsible for getting nutrients to the plant roots, in a form acceptable to them.
In the final soil phase, gases, we are most concerned with oxygen and carbon dioxide. Oxygen is just as necessary to plant roots as it is to all living animals. This is why plants cannot do well in waterlogged soil.
Water is not the only factor to influence the absence of oxygen in the soil. Compaction of the soil can have the same effect because there are not enough air spaces within the soil to provide enough oxygen.
Carbon dioxide is respired by the roots as well as the leaves. If there is a build-up of carbon dioxide in the soil because it cannot escape, due mainly to compaction, there is a corresponding shortage of oxygen. Also remember that water drains downward via spaces in the soil.
Unfortunately we only have enough room to discuss clay and silt soils. This is what most of us garden on in the Chilliwack area and are very likely to give us the most problems. Heavy soils are fine textured and are generally poorly drained and therefore become easily waterlogged. These soils get compacted more often and don’t warm up easily in the spring, mainly because of their high water content. This is not always a problem unless you want early crops.
Heavy soils have a great reserve of plant nutrients in them, and are the last to dry out. The best way to improve these soils is by incorporating bulky organic matter like farmyard manure, composted straw, shredded leaves or compost. A very good product Sea-Soil is composted bark chips enriched with fish waste. There is also a similar product with shrimp waste. Crab, lobster and shrimp shells are excellent composts accelerants, as they create heat in decomposition.