Influence of Cultural Practices on Weed Encroachment

Poor turf culture is a major reason for weedy lawns. Any effort to control weeds in turf should start with improving cultural practices (mowing, fertilization and irrigation). Properly implemented primary cultural practices will reduce the turfgrass susceptibility to weed encroachment and prevent conditions conducive to weed growth and development.

Mowing

Increasing your mowing height and increasing your mowing frequency will reduce weed occurrence in lawns. Increasing your mowing height provides a number of benefits, such as deeper rooting, which will translate to increased drought tolerance. Increasing the mowing height will also prevent weed seed germination. Weed seeds are constantly entering turfgrass, but establishment will be substantially reduced by increasing mowing height. The increased mowing height reduces the amount of sunlight that reaches weed seeds at the soil surface.

Increasing mowing frequency will also mitigate weed encroachment by increasing turfgrass density. At a minimum turfgrass should be mowed once a week, while putting greens will likely require daily mowing during period of peak growth. More frequent mowing triggers a physiological response within the turfgrass directing more energy and resources into lateral growth rather than vertical growth. Having denser turfgrass will minimize the establishment of annuals grasses, like crabgrass, and annual bluegrass.

Acceptable mowing heights for commonly used turfgrasses are below.

Mowing Height Ranges for Northwest Turfgrasses

Turfgrass species

Optimum Height Range (inches)

Bentgrass (colonial, bent and highland)

0.5 to 1

Fine fescue (chewings, red and hard fescue

1.5 to 2.5

Perennial ryegrass

1.5 to 2.5

Kentucky bluegrass

1.5 to 2.5

Tall fescue

2.5.5 to 3.5