All weeds are plants. Not all plants are weeds. Weeds are a specifiable subset of plants. Specifically, weeds are plants that grow wildly where they are undesirable. Similarly, dirt is likely soil, although it could be anything that is dirty. Soil is not merely dirt, though. Dirt is soil or a similar matter, where it is undesirable. Plants and weeds know the difference.

Most simply, soil is the loose material on the surfaces of most land. Obviously, looseness is relative. Some is quite dense and hard. It is not solid rock though. All of it consists of a combination of various inorganic aggregates. Most also includes various organic matter. Inorganic aggregates range in size from microscopic clay particles to substantial stones.

Soil provides stability and nutrients for vegetation that inhabits it. Roots disperse through it for structural support of their associated stems and foliage. Roots also absorb nutrients and water, as well as conduct respiration. Soils are naturally quite diverse. Vegetation is naturally more diverse to exploit various soils. Very few soils can not sustain vegetation.

Lawns are the carpets of a garden. Hedges are the walls. Tree canopies are the ceilings. Soils are the foundations. They support all vegetation that is not self-reliant in containers or epiphytically. Some soils are sandy, so drain very efficiently. Some are denser clay, so may drain slowly. Like climate and exposure, soils can limit what grows within a garden.

Most common and popular vegetation is satisfied with most common types of soil. Some, particularly vegetables and annuals, are more demanding. Even within good quality soil, they appreciate amendments such as compost. Amendments improve aeration, drainage and moisture retention. Organic amendments also provide nutrients as they decompose.

The most demanding vegetation also appreciates fertilizers. Most fertilizers are chemical or synthetic fertilizers of very precise formulation. Organic fertilizers are only slightly less precise. All allow application of specific amounts of specific nutrients for specific results. For example, nitrogen enhances foliar growth. Also, phosphorus enhances floral growth, and fruit growth.