Categories of Weeds Lawn weeds are classified according to their longevity and the type of leaves they have. Because certain weed killers are more effective against one type of plant than another, it is important to know what kinds of weeds you are trying to control. All weed plants are either annuals, biennials, or perennials. Annuals grow, set seed, and die within a year. There are summer annuals and winter annuals.
Summer annuals germinate in spring, grow to maturity during summer, and die by fall or winter.
Crabgrass, knotweed, and purslane are summer annuals. In spring they flower, produce a crop of seeds, and die. Examples of winter annuals are annual bluegrass, burclover, and chickweed. In warmer climates, some annuals such as crabgrass can live into a second year. Biennials live for 2 years.