Most gardeners will encounter soil that contains some elements of silt, sand and clay, in varying proportions. In ideal situations, gardeners will have soil with equal parts of silt, sand and clay. The goal when working with any planting soil is to provide nutrients, aeration, water and physical support for the plants. Assess your soil and then choose plants that will grow in it or amend the soil based on the characteristics of its particles to achieve a good growing medium.
Clay soil is composed of very small particles. The particles pack down tightly and inhibit a plant's root from growing. Soil compaction means that clay soil drains poorly. When clay is wet, it tends to hold onto the water producing a soggy, slippery surface. It takes clay a long time to dry. When clay is very dry, it tends to crack. Plant roots cannot span the gaps in dry clay and the plants do not survive. Clay holds nutrients well; however, the problems with compaction make it difficult for plants to access and use the nutrients. Improve clay soil to reduce soil aggregation, increase porosity and permeability and improve aeration.
Silt soil is composed of small-sized particles. Its particles are larger than clay, but much smaller than sand. Silt feels smooth or similar to the texture of flour when you rub it between your fingers. You can usually trace the origins of silt soil back to a river. There is very little space among silt particles for water or air molecules. Silt packs down tightly and it is difficult for roots to grow in it. It is not usually prone to water over-saturation. Amend silt with organic material to increase space for oxygen, carbon dioxide and water.
Sand particles are large and there is a lot of space among the particles. Sand drains well because of the space among the particles. Sand holds nutrients poorly for the same reason. Sand feels gritty to the touch. It is typically a light colored brown. Gardeners with sandy soil need to water their plants more frequently than they would if the same plants were in clay, silt or loam. Amend sandy soil with organic matter to help it to retain nutrients and promote plant growth.
Loam is soil that blends equal amounts of silt, sand and clay. It is brown and has a crumbly texture. Loam is light and offers little resistance to digging. Loam is naturally high in nutrients and can make these nutrients available to plants when they need it. Most gardeners desire a loam soil because it is a superior growing medium for plants. The combination of different particle sizes allows liquid to pass through the soil at a rate that makes water and nutrients available to the plant's roots.