Pull stiltgrass now or you will be sorry
If untended areas of your garden are rife with a bamboo-like grass standing 12-24 inches tall, you might have been invaded by Japanese stiltgrass (Microstegium vimineum).
Now is the time to pull it, before it sets seed. Be thorough. Stiltgass will germinate under and around established plants where few other weeds can survive.
This annual grass grows in open sunny areas and shady hillsides and can crowd out native vegetation. It probably hitched a ride to our country 100 years ago in commercial shipments from China.
I first noted it a decade ago in my garden and thought it might be a seedling of Japanese forest grass (Hakonechloa macra). It was easy to pull and keep under control. But over the past few years, it became clear that despite my efforts, it was spreading. Everywhere. Currently the woodland behind my property is heavily colonized with stiltgrass, and it’s pervasive in local parks, road cuts and wild areas.
Stiltgrass germinates in the spring and grows slowly through the summer months, according to a Penn State Extension publication. Although its root system is shallow and weak, it spreads through a high production of seeds and by sprouting new shoots from the stems that come in contact with the ground. A single plant can produce between 100 and 1,000 seeds that 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, 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, you can eradicate this weed in your garden over several years. You will need to be vigilant for its reappearance because it is so widespread in our area.
Stiltgrass can be identified by the distinctive white mid-rib on its leaves. It is often found comingling with native whitegrass (Leersia virginica). After a period of active growth and seed production, it dies back, leaving a thick layer of tan thatch until it reappears the following spring. It is unpalatable to deer and crowds out native vegetation, including tree seedlings in local forests.
To mitigate its spread in larger areas, use a line trimmer.
Whack plants back as close to the ground as possible. It is critical for this to be done before seeds appear, so if you tackled it in early summer, be sure to hit it again now. Another option for controlling its spread is to smother it with grass clippings, cardboard or plastic. For suggestions on chemical control, go to https://extension.psu.edu/controlling-japanese-stiltgrassin-your-garden.
Once stiltgrass has been eliminated, plant with more aggressive, desirable plants that can outcompete it. Some may be on the invasive side, but that’s what it takes to stand up to the vigor of stiltgrass.
In shaded areas, try ostrich fern (Matteuccia struthiopteris) or sensitive fern (Onoclea sensibilis). Shrubs include Carolina allspice (Calycanthus floridus) and bottlebrush buckeye (Aesculus parviflora). In sunnier areas give mountain mint (Parth
-enium muticum) a try, beebalm (Monarda spp.), dwarf Japanese garden juniper (Juniperus procumbens ‘Nana’) and ‘Annabelle’ hydrangea (Hydrangea arborescens).
It can be daunting to see large stands of stiltgrass in your neighbor’s yard or wild areas adjacent to your property. Despite your efforts, it will still pop up in your garden next year. Draw a line, perhaps by planting shrubs that screen off areas impacted by invasive plants. Decide where you can realistically win the stiltgrass battle, then add a bench, pour a glass of wine and enjoy that space.