One of the most locally-prolific of all invasive species present in North America is Japanese Stiltgrass[1]. An annual grass that spreads via seed, it, once it gains a foothold in an area, it has the ability to spread so prolifically in sunny or shady areas that it resembles a monoculture or carpet. While it can look lush and pretty during the growing season, it will be ugly all winter long as it covers every square inch of ground in a yellow carpet of dead grass.
I hate this grass as it does almost nothing for the North American ecosystem. Outside of a few insects, nothing really eats it and thus it just proliferates! And I’ve been battling it for several years in the woods behind my home.
When we moved in, there was no Japanese Stilt Grass – only another invasive, Bush Honeysuckle, which created such a thick canopy that nothing would grow below. After spending a couple years eliminating that, the stilt grass from surrounding areas moved in with a vengeance, and almost instantaneously. Yay, fun, a new invasive to battle!
The way to stop Japanese Stiltgrass
Japanese Stiltgrass is an annual grass, meaning that it grows from seed in spring, lives and will die by winter. But, in late summer, it will set seed. The seeds will be at the top of the stalks/culms, and will happily stick to clothes or fur of passing animals, enabling it’s spread. So, your goal each year, until you have a handle on the infestation, is to prevent Japanese Stiltgrass from setting seed. And that is repeated over and over by many authorities and institutions, that “reducing seed production may be the most cost-effective management strategy of Japanese Stiltgrass” [Hubner 2011].
How long are Japanese Stiltgrass seeds viable?
Japanese Stiltgrass seeds remain viable within the seed bank for 5 years[2]. I’m working to test this theory now, as I’ve been pulling or string-trimming it for three years….
Set your goals based on infestation/surrounding property
So, I’ve been trying different methods, and will outline them below with the various degrees of success or failure! But, one thing you absolutely must understand is that if you are unable to completely eliminate the infestation from surrounding land adjacent to yours (for instance, a neighbor who won’t allow you to go on their property to kill it), then your goal must not be to eliminate it completely, but establish natives that are able to compete with it.
The reason for this is that the seeds will stick to the fur of deer, rabbits, or other animals. And those seeds will just find their way back to you one way or another over time. So, if there is land adjacent to yours that has populations of stilt grass present, you either need to kill those too (for multiple years) or else you will have to fight it all over again. Because the seed from the grass growing on land you don’t control will find it’s way back to your land in time. That is just the unfortunate nature of invasive species – they propagate themselves and spread on their own.
Methods of controlling Japanese Stilt Grass
There are five predominant methods for controlling Japanese Stilt Grass. Two chemical methods and three mechanical methods that have proven successful[4][5].
Chemical
For chemical control there are two strategies, pre-emergence and post-emergence.
Pre-emergence control
If you are attempting to control Japanese Stiltgrass in your lawn or flowerbeds, there are several pre-emergent herbicides that can be effective. Pendimethalin, Imazapic, and sulfometuron all will stop the seeds from germinating. Each of these should be applied 2-3 weeks before the seed germinates. Using pre-emergents can be a good strategy for areas where you can’t easily pull the plant later, such as when it is growing closely among other desirable plants.
Post-emergence control
If there is a large infested area, one where it appears to be total or near monoculture of Japanese Stiltgrass, then post-emergent herbicides can be very effective. Round Up (glyphosate), and Finale (glufosinate) both will work on Japanese Stiltgrass. But, like mechanical control, you need to do it before the grass flowers and begins producing seed. The most effective time to kill the grass before seed is produced is generally late Summer (early to mid-August in zone 6/7).
Mechanical
Small infestations or large infestations in cleared areas can be mechanically controlled. You should do this in late summer, before the seed begins to set. For reference, this occurs in the woods near my in early September, so I always make sure I pull the grass by Labor Day.
Weed eater / string trimmer
Using a string trimmer is probably the easiest method to kill Japanese Stiltgrass, as you just need to be able to wield a trimmer. Simply cut it low to the ground. And again, if you do this before seeds set, the plant will not have time to make more seeds before frost.
Pulling by hand
Japanese Stiltgrass is easy to pull by hand, particularly after a rain when the soil is moist. I like to use bare hands but apply some DEET for ticks to my forearms, knees, and ankles. But stiltgrass has it’s roots built on stilt-like structure that are shallow – so you will have no problem pulling it up.
What I’ve found to work best is to just run your hand through a patch, trying to gather up as many stems as you can and then pull. It should all come out easily with little to no resistance. If you are finding some resistance, then it is likely that there are other plants mixed in the ‘bunch’ you grabbed. When I encounter this, I let go and try to isolate the other plant, as often it is a native that I want to keep. In fact you can often just loosen your grip a small amount, and the natives or non-stiltgrass plants will slip through your fingers, but the Japanese Stilt Grass will pull out.
Suppression through competition
Part of your strategy will likely be keeping the stilt-grass down via competition from other natives. Since Japanese Stiltgrass doesn’t germinate until roughly mid-spring, most other native grasses and flowers will have emerged before it, and can likely out-compete it. So, if you cover the ground in natives you can effectively steal available ground for the JSG seeds to germinate. AKA – it can’t move in if there is no vacancy on the ground!
List of plants that can compete with Japanese Stiltgrass
Since I started my battle with stiltgrass, I’ve been experimenting and testing different plants that can survive an infestation of stiltgrass, and hopefully beat it! So, below I will give a rough list and comments of plants that seem to be holding their own against Japanese Stiltgrass. One theme you will notice in this table, all of the plants have some form of natural deer resistance….
| Species Common Name (Scientific Name) | Growing conditions | Comments |
|---|---|---|
| Bee Balm (Monarda didyma) | Full sun to part-shade, moist to medium-moist soil | As a competitor to JSG, this does best in full sun & moist conditions. It will do ok in part-sun and on slopes. The rhizome spreading is a real bonus! |
| Blue Mist Flower | Full sun to part-sun | Aggressive member of the mint family. Spreads via rhizomes. |
| Blunt Mountain Mint (Pycnanthemum muticum) | Full sun to part-shade, dry to medium-moist soil | This plant is the champion! It grows well enough in part-sun and spreads via rhizomes each year. It is probably the best at out-competing stiltgrass. |
| Black Raspberry (Rubus occidentalis) | Full sun to part-sun, mesic to moist soil | this works well in part-sun areas. It is somewhat aggressive itself, and will do well among stilt grass. |
| Pennsylvania Sedge | Full sun to shade | A low, clump-forming/spreading sedge that only gets 12″ tall. This plant is a great ally in that it will firmly occupy ground that prevents stilt grass from germinating. |
| Purple Giant Hyssop (Agastache scrophulariifolia) | Full sun to part sun, moist to medium-moist | The size of this plant, plus the seed it generates make it a good competitor. I’ve established several populations around my forest, and they are doing great. |
| Violets (viola sp) | Full sun to full shade, mesic to moist | Violets are shade tolerant flowers that spread via seed and rhizome. I have a nice population that has not been beaten, and seems to be spreading. |
| Virginia Bluebells (Mertensia virginica) | Full-sun to full shade, mesic to moist soil | This plant is more of an honorable mention. It can grow and out-compete stilt grass. However, it is an ephemeral. So it will often just delay germination of Japanese Stiltgrass, as it is falling down by mid-June |
| Virginia Wild Rye | Full sun to shade | A native grass that is a short-lived perennial, it can grow in full shade – enough said! |
| White Snakeroot (Ageratina altissima) | Full sun to part sun | Aggressive member of the mint family. It spreads via rhizomes, and does well in both moist and dry conditions. |
| White Wood Aster | Part-sun to shade | I’ve had this plant growing pretty well in shady, dry conditions among Japanese Stiltgrass. It doesn’t seem to be the best competitor, as it is slow to spread, but is doing well. |
So, are there other plants that will compete well? Most certainly. In fact I would think any plant that can tolerate some shade and moist soil, has a natural deer resistance (I’m looking at you, mint family), and can spread readily on it’s own will be a good candidate. Now, many of these qualities make it undesirable for regular gardens. So, know that if you have flowerbeds you probably wouldn’t want to plant all of these within or nearby without a strategy to stop them from spreading.
Mulching to prevent seed germination
On other strategy can be to apply a fresh layer of mulch in Autumn or early Spring to prevent seeds from germinating. Whether you are using leaves after the stilt grass seed has dispersed, or you are using wood chips, a 2″ layer should be sufficient to stop seeds germinating.
Perseverance
Fighting off Japanese Stiltgrass is a job that requires tenacity and persistence. I’ve been battling it for three years, and hopefully I only have a few more before I can exhaust the seed bank and have it suppressed.
Unfortunately this invasive species is not going away. It has firmly established itself in so many corners of the country that it will likely be here forever. So, I’m doing my part, one yard at a time to try to beat it back and create a healthier ecosystem in doing so.
Find more gardening tips here
References:
[1] – Microstegium vimineum (Trin.) A. Camus, USDA NRCS, accessed 19DEC2024.
[2] – Barden, Lawrence S. “Invasion of Microstegium vimineum (Poaceae), an exotic, annual, shade-tolerant, C 4 grass, into a North Carolina floodplain.” American Midland Naturalist (1987): 40-45.
[3] – Huebner, Cynthia D. “Seed mass, viability, and germination of Japanese stiltgrass (Microstegium vimineum) under variable light and moisture conditions.” Invasive Plant Science and Management 4.3 (2011): 274-283.
[4] – Japanese Stiltgrass, National Invasive Species Information Center, US Department of Agriculture. Accessed 20DEC2024.
[5] – Hubbard, Pamela T. Controlling Japanese Stiltgrass in Your Garden, Penn State Extension. Accessed 19DEC2024.
Recent Posts
All homeowners like to keep their yards looking their best, and having a well-defined edge or border between your lawn and flower bed can greatly improve the appearance or curb appeal of your yard....
Common Milkweed is a perennial wildflower native to North America. It is one of the plants that Monarch Butterflies (the Asclepias genus) will lay their eggs on, and as such is critical to their...