Few people look over the garden fence and compliment their neighbors on the quality of their soil. They will speak in glowing terms about the big, bright flowers, luxurious foliage and thick, green lawns, usually without realizing that all of those features depend on good soil. Healthy soil is alive with organisms. It holds oxygen and nutrients and has space for water to flow and roots to grow. Without good soil, there is little chance you will have a good garden.
The color of the soil provides information about the characteristics and quality of the soil for plant growth. Darker soil contains more organic material than lighter soils, according to Cornell University's Soil Basics guide. Furthermore, adequate air in the soil and good drainage shows up as a brown-red color. Blue-green or a gray color means that the soil is continuously wet. Yellow soil indicates a drainage problem. Colors that appear to be streaked suggest a seasonal or periodic drainage problem.
The texture of soil is the relative levels of sand, clay and silt that it contains. Soil that is composed primarily of sand particles has the coarsest texture. Clay soil has the finest texture. Soil that holds roughly equal portions of sand, silt and clay is loam. The texture of loam falls near the midpoint between sand and clay. Soil that is mostly silt, is coarser than clay, but finer than loam.
The structure of the soil describes how the particles of clay, sand and silt in the soil clump together. When the soils clumps together it forms aggregates. Gardeners and soil specialists test the structure of the soil by collecting some of the soil in their hands. The soil has good structure if it crumbles easily. Air and water move rapidly through soil with good structure. Good structure encourages root development because roots expand using the same channels through which air and water travel.
The Arizona Master Gardener manual explains that soil drainage is "the rate and extent of water movement in the soil, including movement across the surface as well as downward through the soil." Texture, structure and the physical condition of the surface and subsoil layers all play a role in determining how well the soil drains. Soil drainage is significant because too much water suffocates plant roots and too little water causes plants to wilt and die.
Organic matter refers to the part of the soil that is "composed of both living organisms and once-living residues in various stages of decomposition," according to the National Sustainable Agriculture Information Service. Soil rich in organic matter retains nutrients and water more efficiently than soil devoid of organic matter. Gardeners must replenish the organic matter in their soil annually to compensate for the amount lost due to microbial activity.