Lawn Weeds in the Pacific Northwest

Lawn weeds can infiltrate turf grass in newly seeded or established lawns. Wet winters and dry summers make for an adaptable set of turf weeds in the Pacific Northwest. The first step in controlling weeds is to properly identify the most-persistent species in order to understand their life cycle and growth habit. Broadleaf herbicides are commonly used to eliminate turf weeds. When you know what weeds you have and how they work, you are able to make more informed decisions that will ultimately improve the health and appearance of your lawn, as well as manage problem weeds.

Yellow dandelion flowers (Taraxacum officinale) are a familiar sight in lawns across the United States. A deep-rooted perennial with toothed leaves, dandelions prefer sunny locations and produce seed from spring until frost. If not fully removed from the ground, their thick roots will resprout. Physical removal can be adequate to control moderate populations, as well as mowing at the flowering stage to prevent seed dispersal.

Broadleaf (Plantago major) and Buckhorn (Plantago lanceolata) plantain are perennials with fibrous roots and leathery leaves that grow in a rosette form. Their leaves have strong parallel veins and set flower spikes that bloom from May to September. Plantain spreads by clumping as well as seed dispersal. Physical removal and mowing are often adequate to control the spread of plantain weeds.

Clovers (Trifolium sp.) are perennials in the legume family, meaning they can fix nitrogen from the air, which helps them succeed in underfertilized lawns. Clovers grow low to the ground, resisting control through mowing, preferring slightly moist sites and sending up globe-shaped white or pink flower clusters May through November. They reproduce both by seed and by spreading via runners into thick stands that out-compete the desired turf grass. Many homeowners allow clover to persist in their lawns because of their ability to add nitrogen to the soil. A regular fertilization program with a high-nitrogen ratio may help to discourage clover.

Moss (Selaginella sp.) becomes a turf weed in lawns west of the Cascade Mountains where turf damage from summer drought creates patchy turf -- the perfect setting for moss to grow during the mild winter months. Grass kept too tall or compacted soil also create ideal growing conditions for moss, which reproduces through spore dispersal or by breaking apart and relocating via wind, water or human movement. Moss is a poor competitor and can be discouraged through keeping turf grass properly fertilized and watered during active growth.

Annual bluegrass (Poa annua) germinates in late fall and grows rapidly in the mild winters west of the Cascades. Growing more quickly than the desired turf bluegrasses and fescues, annual bluegrass out-competes other grasses then dies, leaving bare spots in the lawn. Following a good fertilizer schedule and watering deeply but infrequently helps to establish the desired grasses, making them better able to compete against more vigorous weed species.