A Garden Tail: How To Eliminate Japanese Stiltgrass

Japanese stiltgrass (Microstegium vimineum) is a highly invasive summer annual that germinates in early spring (March–April) and dies back with the first autumn frost. It spreads through a persistent seed bank that can remain viable in soil for up to five years, making eradication a multi-season effort focused on preventing seed production.

Because stiltgrass has a shallow root system, small infestations can be pulled by hand when soil is moist. The most effective timing is late August to early September—just as seed heads begin to form but before they mature. Early-season disturbance is discouraged, as it can trigger additional germination from the seed bank. Routine mowing is also ineffective, as the plant can set seed below typical cutting height.

For larger infestations, targeted treatment depends on location. Pre-emergent herbicides such as Preen can be applied in early spring (March–April) to block germination. During active growth (May–August), selective herbicides like Ortho Grass-B-Gon can be used in ornamental beds, while spot treatments with glyphosate-based products (such as Roundup) may be applied carefully where complete vegetation removal is acceptable.

After removal, soil should be immediately covered or replanted. A 4–6 inch layer of mulch helps block light and suppress new seedlings, while dense plantings of competitive, non-invasive species can reduce future infestations by shading the soil surface.

For official identification assistance and localized university research, consult the Penn State Extension Guide on Managing Japanese Stiltgrass.

 

RETURN TO GARDEN TAILS STORIES & TIPS