Soil is the weathered outer layer of the Earth’s crust and is a mix of tiny rock fragments and organic matter. The three broad categories of soils are clay, sandy, and loam. Clay soils are heavy, with the particles sticking close together; most plants have a hard time absorbing the nutrients in clay soil, and the soil tends to become waterlogged. On the other hand, these soils can be good for a few deep-rooted plants, such as mint, peas, and broad beans. Sandy soils are light and have particles that do not stick together, which is good for many alpine and arid plants, some herbs such as tarragon and thyme, and vegetables such as onions, carrots, and tomatoes. Loam soils are a well-balanced mix of smaller and larger particles that can provide nutrients to plant roots easily. They also drain and retain water well, and thus are considered ideal for plant growth.