Weeds are plants that grow well in disturbed habitats, plants that are not wanted, or that interfere with human activities or natural systems. Traditionally, undesirable plants are controlled using preemergence herbicides, postemergence herbicides, biocontrol, and cultural management which is the use of primary cultural practices mowing, fertilization, and irrigation, and other methods to adjust environmental conditions to make them more suitable for desirable turfgrasses. Prevention, quarantine, and control of satellite populations are very helpful.

In turfgrasses, weeds are classified into broad botanical groups (broadleaf, grassy, and sedge), life cycle groups (perennials, biennials, and annuals), and functional groups (noxious weeds, exotic invasive plants, and ruderal plants). Ideally plants of all kinds should be identified by scientific name which is a latinized two-part name, but sometimes these broad groups make it easier to generalize and communicate. Accurate identification of unknown plants is necessary to prevent new weeds from getting established.

Weeds occur in lawns, golf courses, sports fields, and other areas because the environment makes it possible for them to compete with the planted turfgrass species. Natural grasslands normally support species diversity including broadleaf plants which in that situation are called forbs. An urban example of a diverse grass ecosystem has been called, “mixed urban meadow,” and this can provide many of the conservation benefits of turfgrass.

The opposite of a weedy turf is a monoculture, a turfgrass area composed of a single species. This kind of landscape, while requiring more attention to chemicals to perpetuate a monoculture, can often perform best for high intensity use such as golf courses and sports fields.