In Defense of Stiltgrass

Japanese Stiltgrass (Microstegium vimineum) is a much-maligned “invasive plant,” but I don’t believe it deserves this reputation. Call me crazy, but personally, I love stiltgrass. And why not? She is beautiful, like a tiny bamboo forest. She clothes herself in a luxurious green and beams with lushness every morning dew. And she is also helpful… but I’ll get to that later.

Japanese Stiltgrass (Microstegium vimineum)

Originally from east Asia, stiltgrass was introduced accidentally to Tennessee around 1919, after having stowed away from China in some packaging materials. Stiltgrass is an annual, seeding profusely, and able to remain in the seed bank for several years. Unusual for most grasses, stiltgrass grows in low-light conditions.

It has been claimed that stiltgrass invades healthy, biologically diverse, native plant communities. My own observations do not bear this out. What I see is that stiltgrass is especially abundant in recovering first-growth forests – places bearing a history of anthropogenic degradations and exploitations. Young woodlands with stiltgrass understories, like the ones I see around the southeastern USA and mid-Atlantic states, may be characterized by pioneering species like tulip poplar (Liriodendron tulipifera), black cherry (Prunus serotina), black locust (Robinia pseudoacacia), red maple (Acer rubrum), and box elder (Acer negundo).

Tulip poplar, red maple, and box elder all have something in common: wind-born seeds. And black cherry is planted through bird droppings. Black locust can be dispersed by wind as well as by birds. Other species I commonly see among the stiltgrass community are shrubs such as bush honeysuckle (Lonicera maackii), vine honeysuckle (Lonicera japonica), autumn olive (Elaeagnus umbellata), barberry (Berberis thunbergii), and multiflora rose (Rosa multiflora), all of which are also planted by birds. These dispersal vectors are important considerations, and they suggest a meaning.

Important questions to ponder are how and why such a particular assemblage of species comes to be in a place. One thing to consider: in such areas, there is no longer a native seed bank! If the native seed bank is gone, it is almost always for one reason, and one reason alone – agriculture. Looking back in time, perhaps the place was once an agricultural field where many years of plowing and tilling destroyed the seed bank. Or maybe it was once pasture land, and many years of over-grazing and trampling destroyed the seed bank.

In either case, the forest that we now see growing up before us is the community that it is because that’s what is able to be there now. Whatever blows in on the wind. Whatever falls out of the sky from a passing bird. That’s what grows!

As for how stiltgrass enters an area, there are a few possibilities. It is possible, I imagine, that the seeds could be dispersed through the belly of some small creature, a rodent perhaps, and germinate after coming out the other end. Stiltgrass seeds also have “awns” – little bristles, making them something like velcro – and this allows them to stick to the fur of mammals. They could be hitch-hikers on the tawny hides of the white-tailed deer, or on the scrappy pelts of raccoon or possum. Stiltgrass can also grow clonally from her many nodes, and so if they wash downstream, they can sprout wherever they settle. Flooding can move the seeds around, too.

The invasiveness of stiltgrass is overblown and taken out of context. This is my opinion, but it is more than that, too. Flory et. al. 2017 found that “The invasive grass was initially abundant and suppressed native species, but invader decline over time corresponded with succession to native herbaceous species dominance when fire was applied, and to native tree dominance without fire such that after 8 years, the initial effects of invasion were no longer apparent. Thus, our data provide some of the first experimental evidence that while the initial effects of plant invasions can be dramatic, invaders and their impacts may decline over time.” That stiltgrass declines over time has been echoed elsewhere in Cunard & Lankau 2017, too.

Contrary to what is commonly claimed, stiltgrass does not invade older-growth forest ecosystems. It can be ruled out here because the grass does not seem able to thrive where leaf litter accumulates thickly. I see stiltgrass cropping up only where the leaf litter is thin, or bare. Oak leaves, for example, are thicker and tougher than red maple leaves, which are thin and brittle. This is why you’ll see find red maple in the canopy above stiltgrass, but seldom oak. I have also observed where sudden changes in grade or hydrology results in tiny patches where leaves have been swept or scoured away, allowing for a small bit of stiltgrass to grow in the interval. I conclude from from this that leaves smother stiltgrass, forming too great a barrier to allow for seed germination, and only where leaf litter is thin or nonexistent can stiltgrass get a foothold. If my assumption is correct, stiltgrass could be discouraged or eliminated through annual applications of leaf mulch.

Japanese stiltgrass seedling success is restricted by mulch — leaves, wood chips, or in this case, even its own mulch from last year!

Stiltgrass does provide some beneficial ecological services. By holding onto moisture throughout the summer months, stiltgrass orients soil pH towards neutral. Moisture levels and pH are closely correlated (Soil pH Changes Where Wet and Dry Climates Meet), and stiltgrass does a good job of making sure the soil remains somewhere right in the middle, not too wet, and not too dry. Circumneutral soils tend to be more fertile, and soils beneath stiltgrass are high in phosphorous (McGrath & Binkley 2009) and nitrates (Kourtev et. al. 1998), which the stiltgrass seems to consume in large quantity (Kourtev et. al. 1999).

A stiltgrass woodland and a young, pioneering forest.

Some of the beneficial aspects of stiltgrass are synergies – happy accidents, if you will. It is known that earthworms are especially abundant in degraded ecosystems such as young woodlots, where soils are more bacterially-dominated. If it weren’t for the living mulch soil cover that stiltgrass provides, it is conceivable that earthworms would leave the soil exposed, denuded — in other words, oxidizing and damaged. Stiltgrass is thus playing an important role as a vanguard or pioneering species, entering degraded woodlots, and building or maintaining soil fertility until succession steers the species community towards increased diversity and perennial herbaceous plants.

I have a friend who is a bonafide turtle whisperer. On a hike together, my friend told me he could find a turtle anywhere. “Really?” I said, dubiously. “Prove it!” So he looked around, and within a few seconds pointed. “See! There’s one right over there!” I looked, and sure enough, he was right. Standing there, camouflaged by leaves, and hidden beneath a bush, was a box turtle. My friend continued pointing out turtles throughout the duration of our hike. Snapping turtles, box turtles, painted turtles, map turtles. You name it, he will find it. Some people possess seemingly mystical connections with the living beings around them.

One time this friend told me he finds the highest density of box turtles among the stiltgrass. Maybe they eat the stiltgrass, I wonder to myself. Or maybe they like the moisture. Whatever the reasons may be, I trust in his observations!

Stiltgrass can act as a protector of native plants in otherwise inhospitable conditions. Driving down a rural road in the springtime, I find dense blooms of bloodroot (Sanguinaria canadensis) growing right up along the edge of the road in full sun, enshrouded in the brown mulch of last year’s stiltgrass stems. As the summer unfolds, and the stiltgrass grows up green and fresh again, the grass will shade the soil and hold onto moisture, replicating bloodroot’s sensitive woodland habitat requirements.

I also see stiltgrass act as protector where I see bluebells (Mertensia virginica) growing in full sun in the middle of a powerline cut. Again, the dead stiltgrass in the springtime forms a mulch around the plants, shading the soil and keeping temperatures lower, as if the bluebells were growing natively in the mesic woodland soil which they need. And again, as the stiltgrass arises green in the summer, she keeps the soil temperatures cool and moist, allowing the bluebells a safe dormancy period, free from the fear of drying out.

Understanding does not come through isolation, but through an exploration of connections. We must look beyond the reductionist lens of western science. There is a bigger picture unfolding. My gripe with invasion biology is that I don’t want to label, defame, and explain away a plant, I want to understand it! Ecology isn’t about right and wrong, it is about interactions within a system. Invasion biology begins with a naturalistic fallacy, and it cannot survive Hume’s guillotine.

Besides – invasion biology is an abnegation of our own responsibilities.

It is important to point out, that “invasive species” exist first and foremost where land has been degraded by humans, or is being kept in a constant state of disturbance by human activities. The exception — where species introductions do have dramatic and exaggerated effects — are ecosystems like those of islands, where vast expanses of surrounding water act as natural barriers to what would otherwise be the ongoing flow of an open system.

Despite anthropogenic factors being the number one cause of invasions, a look at the Global Invasive Species Database reveals something interesting. Homo sapiens isn’t listed among the top invasive species on this planet. We don’t even make the Top 100 Worst list. In fact, we aren’t listed at all! What’s up with that? The whole thing reeks of politics!

On an animist level, every living thing is being and breathing and beating and the web of life is constantly spinning and unspinning. Each and every present moment is a mere flicker in the universal fires of change. If we could speed up time, it would flow with the turbidity of a waterfall. Who are we to say that a species does or does not belong to the place where it is found? The notion of a native species is conceptually useful, I admit, and I use it too. But under scrutiny – on a genetic level perhaps – the old nativist ideals fall apart. Rapid evolution, for example, has resulted in American stiltgrass populations which are different from their east Asian progenitors in flowering-times, fecundity, size, and vigor (Flory et. al. 2012). In other words, stiltgrass has naturalized and is developing its own genetic distinctions. We are always adapting to the novel conditions we find ourselves in. Take a species out of its native country, wait a few generations, and it isn’t the same anymore.

The whole question of native vs. exotic reminds me of my own heritage. How do I fit into this North American continent when my ancestors came from Europe? I come from a lineage stuck between worlds, no longer European, but not fully American either. The story of stiltgrass is the same kind of story. We cannot step backwards in time, nor can we erase the past. We must make do with the situation we’ve inherited, learning to cooperate, and learning to live in peace. That is why I cannot get on board with invasion biology. It is a philosophy which urges us to wage a war on nature. It condones the use of poisons. It condones the use of chainsaws which lay to waste without use. It compels the wanton slaughter of animals deemed harmful. It condones the deceitful use of Judas goats, and hunting by helicopter. It condones what is an analogue for dehumanization – a dreadful devaluing that cuts into the core of our own hearts. It calls for literal genocide. That is unconscionable.

But I am being too laissez-faire, I hear my critics say. “We must take responsibility for nature,” they say, and find ways to “control the invasives.” Well, I’ll go ahead and answer that charge, providing here my own solution to the “stiltgrass problem.” One which doesn’t use poisons. One which doesn’t devalue the plant. One which doesn’t call for genocide.

Something that is great about stiltgrass is that as an annual which grows only during the warm season, when it dies back in the autumn and winter it creates a wonderful, straw-like mulch. This mulch is ideally suited for burning. Fire introduced to stiltgrass mulch moves in cool-burning, quick fire. Paradoxically, the presence of abundant stiltgrass in rich, shady, degraded habitats provides for its own solution – fire management!

Through the burning of stiltgrass, we can:

  • Clear away weeds and other pesky brambles such as multiflora rose, vine honeysuckle, and other “offenders.”
  • Conduct burns in areas that would be otherwise too moist to burn without the presence of stiltgrass. This is an advantage because the moist areas are often the most overgrown, inaccessible, and fertile.
  • Move forward ecological succession through the opening up of habitat, making room for native perennials, for example.
  • Add biochar to the soil, creating substrate for soil nutrients and micro-organisms, facilitating a higher cation exchange capacity, and tending towards a soil chemistry which is more circumneutral in pH.
  • Through neutralization of soil, increase the bioavailability of calcium thus stimulating root, tuber, and fruit growth of nearby plants, as well as phosphorous.
  • Use fire to further ecological succession, favoring fire-tolerant thick-barked native trees such as oaks and hickories, perennial grasses, as well as perennial herbaceous plants which overwinter below ground in corms, bulbs, or tubers.
  • Use of fire over consecutive years will diminish stiltgrass and promote the growth of others.

The important thing to understand about stiltgrass in order to control it is its timing or phenology. As essentially an annual warm-season grass, stiltgrass will not germinate until early summer. This is after the spring ephemeral bloom. It is also after the time that many perennial seeds will germinate. True, burning stiltgrass clears away last year’s stiltgrass thatch and allows stiltgrass to grow back even thicker and lusher. But that heavy stiltgrass thatch is not just a barrier to its own germination — it is also a barrier to native seed germination. Therefore, with the thatch cleared through burning, over time the stiltgrass populations will lessen as other perennial species, able to re-seed themselves now, begin to outcompete the annual stiltgrass.

Now, here’s a video of some stiltgrass burning I did last year. I burned stiltgrass along a floodplain edge beneath black walnut trees, and also in a larger open area where stiltgrass was growing among porcelain vine (Ampelopsis brevipedunculata), mile-a-minute weed (Persicaria perfoliata), and multiflora rose. Last year’s burn was successful in clearing out a lot of this brush, and there was more grassy growth this year, so I was able to repeat the burn even cleaner than last time, plus I expanded the burn patch further down into the floodplain.

11 thoughts on “In Defense of Stiltgrass”

  1. It is of NO USE to FARMERS!!!!! Cows will NOT EAT IT!!!! It’s going to put me out of farming!!!!!

  2. The stiltgrass that’s growing in the woods of my NC piedmont neighborhood is germinating under leaf litter from various oaks, as well as tulip poplar and sweetgum, hickory and pine. Looking out my window, I’d say it’s probably 50% oaks. But the leaf litter is pretty thin, regardless… maybe the earthworms make short work of it? There are very few understory plants at all in these woods (except for at the edges); a few hardwood seedlings and stems of strawberry bush get nibbled away quickly by the many deers that live here. (To digress: my neighbor feeds the deers corn, and I suspect he’s not the only one doing it.) My property in particular is overrun with sweetgum saplings in my “gardens”; I think the deers are sick of it! Sometimes I lop off a tulip poplar branch from some young trees that I shouldn’t have let germinate near my house foundations — and I chop the branch into sections, spread them out on the ground, and the next little herd that comes by noms off all of the leaves. I was very much worried that the stiltgrass is smothering the seedlings/saplings of other plants that are more valuable to our local wildlife, but it’s true that the bare spots without stiltgrass are mostly… bare. And you can look down the road and see that all of the mature trees are bare as high as a deer can reach. I wish there were some other plant that would fill in under these mature trees instead of stiltgrass — something that would help feed deers, bunnies, rodents, birds, bees, butterflies, box turtles, and all the rest!
    This is the first I’ve heard of stiltgrass dying out over time, leaving the soil better suited to a new growth of natives. I will read the papers you linked above. I hate the idea of burning, though… so much suffering!!!

    1. Thanks you Tara for the response and for your observations. The deer are definitely a big factor in all of this. There has been a correlation noted between earthworms and deer. As soon I can remember who made the correlation I’ll share the name. Anyhow, it has been observed that as soon as deer leave an ecosystem, the earthworms do too. It is a fascinating connection, and very relevant here to our stiltgrass discussion. My theory is that the constant deer browse stimulates root dieback in the woody plants which get their leaves eaten. This is turn encourages bacterially-rich soils, ideally suited for earthworms. When the earthworms move in, they eat up the leaf litter, which allows stiltgrass to flourish. Seen in this way, controlling deer populations by way of apex predators could have an effect of reducing stiltgrass populations!
      – Zach

  3. Thanks for replying, Zach! This article seriously turned my head and made me question my preconceptions about what makes a plant (or animal) “good” or “bad.” Are there other people out there who share your opinion about stiltgrass? (botanists/science-y people, not just random people with opinions, that is!) If so, could you share links to anything they’ve written about it?

    The reason I care so much is that, for the past 4 or 5 years, I’ve written a “Japanese stiltgrass awareness” PSA every summer and posted it on nextdoor.com, which is like Facebook for local neighborhoods. I see stiltgrass spreading through my neighbors’ natural areas, gaining more ground every year, and I worry so much about how it’s preventing native plants from growing, and how that, in turn, is limiting the amount of food available to our herbivores (and pollinators).

    Now the end of summer is nearing, and since I read your article, I’m conflicted about whether to post another PSA — and whether to change the advice I give in it.

    I used to say that stiltgrass smothers native seedlings or prevents germination of native plants by shading or crowding them out. After reading your article, I realized that the stiltgrass in our neighborhood is mostly occupying wooded natural areas that have virtually no other plants growing under the mature trees… so there goes that argument! (Except when it invades lawns or grassy/wildflowery natural areas.)

    I used to advise that people should hand-pull stiltgrass at the end of summer, just before seed heads begin to appear. I emphasize how easy — even kind of satisfying! — it is to pull out, due to its shallow roots. When people reply to my post, some ask about using RoundUp or Acclaim instead of hand-pulling. I personally do not like pesticides, and I say as much, but most people on Nextdoor are conventional gardeners who prefer to spend money on any power tool or chemical spray you can find in the aisles of Home Depot to save time and labor.

    I advise that, for areas of stiltgrass that are too large to completely remove by hand, people should prioritize weeding along the edges of the stiltgrass patch (a few feet in) to prevent it from advancing another few feet next year, as well as scanning all stiltgrass-free areas for stragglers that, if left to reseed, will generate a whole new patch.

    That’s what I’m doing on my own acre as well — every year I weed along the perimeter of my stiltgrass, keeping it in bounds and slowly reducing its coverage over time (in part by leaving the pulled stiltgrass on the ground to smother next year’s germination). I also walk through my woods and pull out any stragglers who threaten to invade my neighbors’ properties.

    Now I’m considering writing my annual nextdoor post (a little late this year), but changing my advice: I may include a link to this article and suggest that stiltgrass in otherwise-barren natural areas isn’t doing as much harm as we think… that its presence is a sign of imbalance, not necessarily the cause of imbalance! I may also suggest prioritizing the removal of any stiltgrass that is growing where other plants are already growing — thus actually competing with native or naturalized species that provide more benefits to birds, bees, and bunnies. In my yard, that’s the “edges” — the places where hardwoods stop and groundcovers (e.g., lawns or “weeds”) begin.

    I very much welcome your thoughts about my plans for my next “PSA.” I do want to point out, though, that when you wrote “Seen in this way, controlling deer populations by way of apex predators could have an effect of reducing stiltgrass populations,” I believe you may have an inverted conception of the [zigzagging] circle of life: usually when we’re talking about playing God with ecosystems, we start by manipulating the plants, earthworms, and herbivores… for the benefit of the apex predators. Whereas you think about manipulating the apex predators for the benefit of the plants! (Which I realize then comes full [zigzagging] circle… still, it was a very thinking-outside-the-box way to look at it!)

    1. I just came back from old growth forest in southern Ohio. Stiltgrass was everywhere.

      Also especially strong in 100+ old second growth forests in Daniel Boone National forest. It’s EVERYWHERE.

  4. Excellent post and will forward on to educate others. I have a small farm (12) acres – very diverse environments from wetlands to high dry forests, two streams, and a vernal pond. And, we have stilt grass. After managing the property without any chemicals at all for 13 years, yep hard human labor, burning, weeding by hand, planting green mulches etc, we still have stilt grass and I too see many benefits of having it, particularly moisture management which has promoted bloodroot spread (YAY!) and also a friend to trillium and jack in the pulpits, ferns too. I also read that it was used as a natural packaging material and I am looking into that as an alternative to recycle some for my own packaging purposes. So my question is do you know if the stilt grass was used in it’s green phase for packaging or was it dried first. I am unable to find any information or data or even stories that tell which way it was used, it just says that it was used as packaging. Thank you again for such a well thought out post…..I wouldn’t even think of taking out the “so called natives” as I have watched our honeybee population and all other native species use them all for habitat and survival.

    1. Because of the high silica content (foliage too course for the palate). When silicaceous plants decompose however they make great soil, which feeds more nutritious plants in subsequent stages of succession.

  5. I am not a farmer but I have 2.4 acres of lawn to mow on my 3 acre rural property. Our land was very overgrown with trees when we bought it in 2012, but we had to clear many trees (approx 60 at the time) to install new septic and just “open up” the driveway and house. We needed a special permit from PA forestry (?) to clear so many trees at once.

    I spent the first two years trying every grass seed mix I could find to grow beautiful lawn on the newly opened and graded areas. From commercial bagged brands to the paper-bag mixes my local soil & stone yards had (these worked much better than the bagged Scott’s or similar mixes).

    But all around the Forrest edges something new started growing. And it did very well. And it filled in the bald areas very nicely. And it grew slower than the tall stringy grasses I was planting, with beautiful coverage.

    Obviously it was stilt grass, and when I learned it was “invasive” I did everything I could to fight it. I had small controlled burns. I bought lots of round-up. I spread weed-and-feed products. And Nothing worked! It just kept spreading. I spent so much time and money trying to be a “good” American and fight this invasive beast. And then I gave up.

    And it is now my FAVORITE grass in my lawn. It is hearty and beautiful. It grows anywhere. It grows slow, so that I only need to cut those areas every other week, compared to the tall stringy blue grass mix that needs to be cut every week. Im telling you, the best looking parts of my (good looking) lawn are stilt grass. And when people comment that I have a nice lawn and have really done wonders with it since clearing the trees, and then ask me what king of grass it is….. they are horrified that I let it live.

    Whatever. The Irish were seen as a foreign invasive species in the 1800’s. Heck, ALL white and black people are non-native species to America. Should we start burning and poisoning ourselves?

    I love JSG. It’s a hearty and beautiful grass.

  6. I really enjoyed reading this article. I have theories on a few “invasive” species and the ecological functions they are providing. But regardless of whether they are “good” or “bad”, they are here to stay unless we begin to manage our wild landscapes on a large scale. Perhaps controlled burns are one way to do so. The sheer volume of participators in nature that are interacting and in relationship to each other is unfathomable and makes it very difficult to really know the effect of one plant or another on the totality of an ecosystem and its evolution. Though I find those who spend the most time observing and interacting with nature come closest to the mark!

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