Weed Life Cycles

The simplest definition of a weed is a plant that grows where it is not wanted. Creeping bentgrass, a turfgrass used on golf courses, is often considered a weed because it is unwanted in Kentucky bluegrass lawns. Weeds are undesirable because they disrupt turf uniformity and compete with desirable grass species for moisture, light, and nutrients. Some weeds are harmful to people because they attract bees, cause skin irritation, or cause poisoning if ingested.

An effective weed management program depends on your ability to identify weeds and to understand their life cycles. This information is essential for developing a good cultural weed management program. It is also necessary for selecting herbicides and for determining the proper time of year to apply them.

Weed Life Cycles

Turfgrass weeds can be grouped into one of three life cycles: annual, biennial, or perennial. Annuals are plants that complete their life cycle in one growing season. Seeds of summer annuals germinate in spring, produce vegetative growth in spring and summer, then produce seed and die in the fall. Winter annual seeds germinate in fall; grow during fall, winter, and early spring; then produce seed and die in late spring. Examples of summer annual weeds are crabgrass and prostrate knotweed. Two winter annual weeds are annual bluegrass and common chickweed.

Biennials require two growing seasons to complete their life cycles. They usually produce vegetative growth the first year, then flower and set seed during the second year. Examples of biennial weeds are yellow rocket and wild carrot.

Perennial weeds live for three or more years (although leaves and aboveground stems often die back at the end of the growing season). Perennials produce new vegetative growth from growing points at or below the soil surface. Perennials also produce new plants from seed. Examples of perennial weeds are orchardgrass and dandelion.