All soils are a mixture of some combination of sand, silt, clay and organic matter. The characteristics of soil vary depending on how much of each ingredient is present. The most important characteristic of soil is its texture, which is determined by the size of the different soil particles. Since most people are not blessed with perfect soil, it is important to identify the type of soil you are working with in order to manage less than ideal garden conditions.
Sandy soil is coarse and does not hold together well. Sand can be as small as .05mm up to 2mm and feels gritty when rubbed between your fingers. It has the most space between particles and therefore does not hold nutrients or water very well. It also has low levels of organic matter and what is present usually breaks down quickly. Sandy soils are described as light. On the plus side, sandy soil is easy to cultivate either wet or dry, quick to warm up in the spring and the acidity or pH is fairly easy to adjust, although it may not last long.
Silty soil is finer than sand and can often be found in flood plains. Silt particles range from .05mm down to .002mm and have the consistency of flour. It makes good farmland but erosion is a problem from both water and wind. It is hard to cultivate when wet and very dusty when dry. It also rarely clumps together, is somewhat slow to warm in the spring and pH is hard to adjust. It can have high levels of organic matter, but it tends to breakdown fairly fast.
Clay soil is heavy and particles are so small that they cannot be seen with the naked eye. They are less than .002mm, feel smooth between your fingers and become sticky when wet. There are tiny spaces between clay particles, which means no room for air. Soil organisms can’t breath and drainage is slow. When it is dry it can be as hard as cement, making it very difficult for plants roots to grow. Clay soil is slow to warm up in the spring and should not be cultivated when wet due to the high risk of compaction. It can have moderate to high levels of organic matter that break down slowly. The pH is hard to adjust but if you succeed, the effects are long lasting.
The best possible soil to have would be a loam. It has equal amounts of sand and silt and a little less of clay resulting in the ideal texture. As a result of the different sized particles, loam has large and small spaces that make it easier for air and water to enter and plant roots to grow. Loams are best for farming and gardening.
There is good news; a simple fix for less than ideal soil textures is to add a lot of organic matter. It can be added as a soil amendment by mixing it into the soil or spread on top of the soil as a topdressing or mulch. Organic matter makes any soil behave more like the much desirable loam. It will help sand stay moist and retain nutrients and improve aeration and drainage of clay. Organic matter also helps maintain the pH balance of the soil. Some excellent sources of organic matter include: compost, aged manure, leaf mold and peat moss. Sawdust, chopped leaves and hay or straw are also good options if worked into the soil in the fall and allowed to decompose before planting.
Secrets of Great Soil by Elizabeth P. Snell
"A Storey Publishing Book" 1998