Soil is the dominant growth medium for plants, though gardeners can also use water as a growth medium. Composting material is used by some gardeners to cheaply restore nutrients and improve the soil overall. While composting is not necessary, composting can reduce the amount of work that gardeners have to do watering their gardens and fertilizing.
Soil is a material made out of eroded rock, organic material and virtually anything else that might happen to be mixed into the soil. Soil forms naturally. Compost, on the other hand, is a deliberate use of organic material to create a nutrient-rich medium that breaks down in the soil, providing plants with nutrients over time.
Both soil and compost contain nutrients that plants need. Compost, however, tends to have more nutrients because the compost has more organic matter, but this organic matter is not available to plants immediately because microorganisms must break the compost material down in the soil.
Gardeners can purchase both soil and compost material. Gardening stores sell potting soil that has all of the nutrients, pH range and silt to clay ratio to create an ideal growing environment for plants. Composting material at stores contains certain organic materials that have a high nutrient content, such as seaweed, or are leftovers from other agricultural processes, such as mushroom composting.
Compost material tends to have more acidity because the decaying organic matter in the composting material releases carbon dioxide, which merges with water in the soil to create more acidic materials. Some soil found in natural environments, however, can have very high acidity if rain frequently washes away the base cations.
Gardeners must work to make both compost and soil suitable for plant growth. Composting material must be frequently turned over so it has adequate oxygen, promoting aerobic bacterial growth. Composting material must stay moist so that microorganisms can thrive. Gardeners must also protect the composting material from scavenging animals. With soil, gardeners must ensure that it is not so compact that the water cannot drain. Therefore, gardeners must till the soil. Gardeners must also worry about the nutrient content of the soil, while compost material naturally contains nutrients. However, gardeners use the composting material to remedy nutrient deficiencies in the soil. Also, the compost improves the soil structure for gardeners with sandy soil by holding moisture so that plants do not experience drought.
Soil is vulnerable to soil erosion caused by wind and water. Compost can help gardeners prevent soil erosion by making the soil structure more sturdy. Plants are also vulnerable to cold temperatures and weeds when planted only in soil, but compost material can serve as high-quality mulch for plants, insulating them and discouraging weed growth.
Gardeners and garden supply stores have to find soil, since soil takes around 200 years to form. Composting material takes a comparatively shorter time, averaging at four to five weeks, but the compost material can take longer depending on the used materials.