Japanese Stiltgrass

Japanese stiltgrass is most likely to be found in moist conditions in part shade.  In some circumstances it can tolerate full sun and, medium shade, or slightly dry conditions.

It is most likely to be found in degraded forest habitats, such as forested urban parks, often along paths and roadsides.  It also sometimes shows up in lawns, especially in shady spots.  Heavy deer over-grazing can also contribute to the sorts of environments that favor this plant.

An easy characteristic to look for is a silvery stripe down the center of the leaf or blade.  The blades also have a fairly rich lime-green color, more intensely green than many other grasses.

The blade shape and dimensions of this grass are somewhat distinctive and exclude many grasses.  The dimensions tend to be around 1¼-4" long, ¼-½" (6-12 mm.) across.  Relative to most common grasses, the blades are wider relative to their length.

One trick for identification, that I was taught by the staff at the Schuylkill environmental center in Philadelphia, relies on this grass's shallow roots. There are some similar-looking grasses that are native, but they are all deeper-rooted.

If you're not sure if you have identified this species correctly, try grabbing it close to the base, and tugging gently.  If it is indeed Japanese stiltgrass, it will pull right out by the roots with little effort.  You will need to pull much harder to pull out the deeper-rooted native grasses.

Japanese stiltgrass, as its name suggests, is an introduced plant, not native to North America.  It is considered an invasive species, and it can damage ecosystems by shutting out native plants.

An additional concern associated with this grass is its weak root system.  Because it is so weak-rooted, it does not hold soil effectively.  As it grows tall and thick, it shuts out and kills many native plants that would naturally have a deeper, more extensive root system.

As this plant spreads, it thus increases the risk of soil loss and erosion during heavy rains and flooding.  As this grass often tends to grow in disturbed habitats and floodplains, the risk of soil erosion in the areas in which it grows can be particularly high.

When removing any invasive plant, it is important to replace it with native plants, or else the invasive can come right back.  There are numerous native grasses, as well as broadleaf herbaceous plants, which can be substituted for stiltgrass, and which can successfully out-compete it once established.

Grasses: An ecologically similar grass which is native, looks somewhat similar, and often can thrive in similar conditions, is Leersia virginica, called "white grass".  Leersia virginica grows best in a rich soil with ample organic material.  A different-looking grass that also prefers similarly moist, partly-shaded conditions is Nimblewill, or Muhlenbergia schreberi; I've found this species to effectively out-compete stiltgrass once it gets established, especially in the slightly gravely soils that it prefers.

In areas with taller growth, I have had good luck replacing stiltgrass with the very different native species Chasmanthium latifolium.  This perennial grass is a little slower to get established, but will eventually grow much taller.  The Elymus genus also contains several species, mostly with a clumping habit, that grow in similar habitat, such as Elymus riparius (Riverbank wild-rye), Elymus hystrix (Bottlebrush grass), and Elymus virginicus (Virginia wild-rye).  These grasses are easy to grow from seed; often, merely scattering the seed in the right habitat is enough to get them established.

There are also many herbaceous broadleaf plants that can grow in similar conditions and out-compete it.

Broadleaf Annuals: Clearweed, Pilea sp., an annual which likes wet areas in part shade.  A taller, somewhat more aggressive plant that has a stronger preference for wet conditions is Jewelweed, Impatiens capensis.  Acalypha (mercury or copperleaf) is another annual plant that can also replace it, liking slightly drier conditions than clearweed.  Acalypha rhomboidea is the most common and vigorous species.

Broadleaf Perennials: Honewort, Cryptotaenia canadensis, is a perennial that often thrives in similar conditions.  A slightly taller-growing native plant, Persicaria virginiana, can establish perennial colonies from underground rhizomes, and also shut out this plant.  Another interesting plant is Boehmeria cylindrica, or false nettle, which resembles stinging nettles but does not have stinging hairs.  Two perennials with showy blossoms in fall, that can outcompete this plant, are blue mist flower, Conoclinium coelestinum, which likes moister conditions, and White snakeroot, Ageratina altissima, which tolerates a wide range of conditions.

I often see these plants growing in similar conditions to stiltgrass, sometimes growing in it and often out-competing it.

References Focused on Invasive Potential and Control:

• Japanese Stiltgrass (Microstegium vimineum (Trin.) Camus) - NYIS - A page on the New York Invasive Species Clearinghouse, focusing on ecological impacts and control methods.
• Japanese Stiltgrass - USDA National Invasive Species Information Center - A federal resource on this grass's invasive potential.