• Soils are complex and varied.Arid soil image by Igor Baryshev from Fotolia.com
  
  Soils are complex structures. They often consist of a mix of mineral particles of different sizes, along with organisms, decaying organic matter and other ingredients. There are, however, several basic types of soil largely defined by the size of their particles. These soils interact in different ways with water, organisms and plant roots, making some better than other for gardening.
  
  

Clay Soil

• Clay soil has the finest particles. They are smaller than 0.002 millimeters in diameter. Because they are so small, the particles of clay soil pack tightly together. Water can only flow in, or infiltrate clay soil slowly. Once it does, it takes a long time to dry again. Clay soil is dense and difficult for roots to penetrate. It tends to dry into a rock-hard surface and can break into chunks when drying. It also does not have the air pockets that roots need to thrive and can suffocate them or promote root rot. This makes it a difficult soil to grow most plants in. On the plus side, clay soil often has very good mineral content.
  
  

Silt Soil

• Silt soil has medium-sized particles, generally between 0.002 and 0.05 millimeters in width. silty soils drain better than clay soils and do not clump like clay soils do. They also have better oxygen content and allow roots to penetrate better. On the downside clay soils can be easily compacted, so they should be turned over or aerated frequently and subject to limited foot traffic. Of the basic soil types, silt soil is one of the most desirable.
  
  

Sand Soil

• Sand has the largest particles of the main soil types, since anything with larger grains is called gravel. Sand particles are generally between 0.05 mm and 2 mm, and can be seen with the naked eye. Sandy soil has excellent drainage and plenty of air. Unfortunately, the drainage is too good; water flows through sand so quickly that it does not provide enough moisture for many plants. Sand is also nutrient poor, and fertilizer added to it can wash through quickly. Many desert plants are adapted to thrive in sand, but for most other plants sand is not ideal.
  
  

Peat Soil

• Peat is an unusual kind of soil found in swamps, bogs and other wetland areas. Whereas sand, silt and clay consist of small particles of rock, peat consists mostly of partially decomposed organic matter, such as dead plants and animal waste, with particles of varying sizes. Because the soil is acidic, the organic ingredients decompose slowly. Peat soils retain water well, and are good for plant growth. They often require extra fertilizer, however, because the organic material in them is not readily available to plants.
  
  

Loam

• Loam is a mix of sand, clay and silt, and can be used to grow nearly anything. Loam contains roughly equal portions of clay, sand and silt. It drains well and has good aeration, but still retains enough water to nourish plants. It also has good nutrient composition and can support the worms and other decomposers that keep the soil healthy. Loam can vary widely in its soil composition and will take on different names accordingly. If it consists predominately of sand, for example, it is called sandy loam.