Q&A: Japanese Stiltgrass
Learn about this invasive exotic weed that thrives in a variety of soil and light conditions.
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Q: I have an unusual grass in my yard. It first appeared at the edge of the woods but has since moved into the sunny areas of the lawn. What is this weed and should I be worried?
— M.K., Tenn.
A: Based on the photo and your description, it looks like your mystery plant is Japanese stiltgrass (Microstegium vimineum). It's an annual weed that thrives in both the sun and shade and tolerates a range of soil conditions. Growing about two to three feet tall, it has alternate, light-green leaves that resemble the delicate foliage of bamboo. Flower spikes bloom in late summer before going to seed.
Native to Asia, Japanese stiltgrass is considered to be invasive in the eastern U.S. It forms dense mats that spread in disturbed and undisturbed sites. Eventually these mats grow into a monoculture, crowding out other plant material.
Getting rid of Japanese stiltgrass can be very challenging. The plants can root from each joint along the stem, and the grass also spreads via seed. Don't use a string trimmer or mower to control this grass since that can help in its spread. An application of glyphosate (one such product is commonly known as Roundup) is effective but may not be ideal when more desirable vegetation is nearby. This herbicide can kill the weeds as well as the good plants. Note: When using any chemical, it is best to read the product label before application and follow label directions.
Japanese stiltgrass can also be removed by hand pulling. This can be labor intensive but may be the better alternative to using chemicals. Be sure to dispose of the pulled grass in the trash; don't add it to the compost pile. Unfortunately, because plant parts can root and the seed can be viable for years, you'll have to stay on top of removing this weed for the upcoming growing seasons.