• A well-drained soil results in healthier plants.Jacqueline Veissid/Stockbyte/Getty Images
  
  Soil type is defined by texture, and texture is defined by the composition of clay, silt and sand within the soil. A clay soil then is primarily composed of clay particles, with silt and sand present in smaller amounts. Soil type or texture directly affects the nutrient content and drainage capabilities of the soil.
  
  

Clay

• Clay is the smallest of the three particles that comprise soil type. These small particles are closely bound together, resulting in a dense and heavy soil. The soil is compact, holds little oxygen and when water is poured onto the soil, the water is held within the soil. Clay particles actually attract the moisture and trap it. For gardeners, this type of soil offers poor drainage. Moisture, as well as the nutrients necessary to plant growth, are trapped by these microscopic particles, and because the water drains slowly, making a thick, compacted mud of the soil, plant roots become waterlogged and fail to access the nutrients.
  
  

Silt

• Silt particles are larger than clay particles but smaller than sand particles. Silt, like clay particles, attract and hold moisture, but due to their larger size, more space is between the particles, making silt more porous. Silt also attracts and retains nutrients, making it a fertile soil. Silt does drain more readily than clay soils, but like clay, the smaller, microscopic particles prevent it from being an ideal gardening soil.
  
  

Sand

• Sandy soils drain quickly. The large size of the particles allows for air and water to pass through quickly. The disadvantage to sandy soils is that they drain so quickly the soil fails to retain a sufficient amount of moisture or nutrients to support most plant life, particularly garden plants. Few plants tolerate the lack of moisture and nutrients. Sandy soil is consistently dry and grainy; it may be devoid of moisture within one to two hours after watering.
  
  

Loam

• Loam is a mixture of all three soil textures: clay, silt and sand. Loam soils vary, but the make-up of well-draining loamy soil has equal parts of silt and sand making up approximately 70 percent of the soil with the remaining percentage consisting of clay. This compositional make-up does not take into account such attributes as chalk or peat moss, both of which would exist in small quantities in common garden soils. Loam soils drain well due to pass through. The silt and clay particles attract and retain moisture and nutrients, but the smaller quantity of clay to the inclusion of sand particles that allow for air and water prevents the soil from becoming too dense.