Practical Remedies for Japanese Stiltgrass

If untended areas of your garden are rife with a bamboo-like grass standing 12 to 24 inches tall, you might be looking at an infestation of invasive Japanese stiltgrass (Microstegium vimineum). Whether an open sunny area or a shady hillside, stiltgrass will thrive to the point of crowding out native vegetation. Japanese stiltgrass is an annual weed that hitched a ride to our country one hundred years ago, most likely in commercial shipments from China.

I first noted it a decade ago in my garden. I thought it might be a seedling of Japanese forest grass (Hakonechloa macra cultivars). It was popping up in beds that I maintained, yet was easy to pull and keep under control. Over the past few years, it became clear that despite keeping my main garden beds free of stiltgrass, its seedlings were spreading. Everywhere. Currently the woodland behind my property is heavily colonized with stiltgrass. You don't need to be an avid gardener to have a garden infested with stiltgrass, it's pervasive in parks, roadcuts and wild areas.

According to a Penn State Extension publication: "Stiltgrass is an annual grass which germinates in the spring and grows slowly through the summer months. Its root system is shallow and weak. It tolerates full sun to heavy shade. Stiltgrass spreads through a high production of seeds and also by sprouting new shoots from the stems that come in contact with the ground. A single plant may produce between 100 and 1,000 seeds that can remain viable in the soil for at least three years. Stiltgrass thrives in areas subject to regular soil disturbances such as flooding, mowing, tilling, and high foot traffic. The small seeds may be carried by animal fur, water during heavy rains, contaminated hay, potted plants, or soil and mud stuck to footwear."

The key to controlling stiltgrass is to prevent it from setting seed. With persistence, stiltgrass can be eradicated in your garden over a course of several years. Because it is so widespread in our area you will need to be vigilant in watching for its reappearance.

Stiltgrass can be identified by the distinctive white mid-rib found on its leaves. It is often found co-mingling with native whitegrass (Leersia virginica). After its period of active growth and seed production, stiltgrass dies back, leaving a thick layer of tan thatch on the ground until it reappears the following spring. It is unpalatable to deer and crowds out native vegetation, including seedlings of trees in our local forests.

Do not delay in heading off a stiltgrass invasion. In areas with small infestations, handpulling will do the trick. Be thorough. Stiltgass will germinate under and around established plants where few other weeds can survive.

To mitigate its spread in larger areas a line trimmer is the best tool. Whack plants back as close to the ground as possible. It is most critical for this to be done before the seeds appear, so if you tackled it in early summer, be sure to hit it again now.  Another option for controlling the spread of stiltgrass is to smother it with grass clippings, cardboard, or plastic. Once the stiltgrass has been eliminated, plant more aggressive, desirable plants. For suggestions on chemical control go to: Controlling Japanese Stiltgrass in Your Garden.

Choose plants that can out-compete stiltgrass. Some of the choices may be on the more invasive side, but these are the plants that can stand up to the vigor of stiltgrass.

In shaded areas, try ferns that will naturalize including ostrich fern (Matteuccia struthiopteris) or sensitive fern (Onoclea sensibilis).  Shrubs that colonize and may outcompete the grass include Carolina allspice (Calycanthus floridus) and bottlebrush buckeye (Aesculus parviflora).

In sunnier areas, try mountain mint (Parthenium muticum) or beebalm (Monarda spp.).  Dwarf Japanese garden juniper (Juniperus procumbens 'Nana') and 'Annabelle' hydrangea (Hydrangea arborescens) have proven inhospitable to stiltgrass in my garden.

It can be daunting to see large stands of stiltgrass in wild areas adjacent to your property or in your neighbor's yard.  Despite your efforts it will still pop-up in your garden next year. Draw the line where the maintained space ends, perhaps by planting larger shrubs that screen off areas impacted by invasive plants. Decide where you can realistically win the stiltgrass battle.