The quality of a garden's soil is in direct relationship to the quality of plant growth and production. Topsoil is the top layer of earth and is where organic matter naturally collects and decomposes. While this may seem to make topsoil the best soil to use in gardens, the quality of topsoil varies from region to region and even from neighborhood to neighborhood. There are many conditions that can affect the topsoil and make it undesirable for planting.
One of the main problems in topsoil in urban areas is pollution. Runoff from streets can bring chemicals including oils from automobiles, tires and spills on the roadway. Manufacturing plants, gas stations, construction debris, fertilizers, pest control, air pollution, water pollution and other contaminants can deplete the nutrients in soil and add plant poisons. Testing the soil before use is recommended and soil amendments should be made to counteract some of the effects of pollution.
Erosion can happen during hard rains when the top layer of soil is carried off, leaving only the coarse or heavier subsoil underneath exposed. In areas where there is little vegetation, erosion happens frequently. In very dry conditions, wind can erode soil, carrying away the dry organic material that is in the topsoil. Hurricanes and tornadoes can also add to this effect. Erosion of soil can be prevented by keeping areas planted.
Soils that hold too much water, very often clay-based soils, can cause a problem for gardens. Plants need oxygen at their roots to survive and if they are in standing water too long, they cannot acquire the oxygen they need. Excessive moisture can also harbor bacteria and fungus which are detrimental to plant life. Soils that are heavy clay-based required additives of sand and organic matter to help with drainage and to add nutrients in the soil.
On lands where livestock feed, it is necessary to be certain that there are not too many animals grazing for what the land can support. If the crops do not get a chance to re-establish themselves, the land can become barren, nutrient depletion can occur, vegetation can die and the soil can become susceptible to erosion, further depleting the nutrients.
Soil that is ideal for a garden or landscape is soil that is dark in color, rich in nutrients and light or spongy in texture and contains large amounts of organic materials. Rich loamy soil allows for moisture retention at the root level for plants to utilize, good drainage, nutrient storage and holds oxygen for the plants to use. If a soil is too compacted, as in clay soils, or too loose, as in sandy soils, one or more of these elements cannot be present in ample amounts for plant growth.