While soil can provide many of the necessary nutrients for plant growth, it may not always be optimal plant health and growth. Urban soils can contain high levels of contaminants such as heavy metals, pesticides, and pollutants, which can be harmful to the plant as well as human health and the environment. Urban soils can be compacted, lacking in nutrients, or have a pH level that is not suitable for growing certain plants. Gardeners may need to amend the soil with the right substrates to improve its quality for ideal plant growth.