Stop Stiltgrass From Taking Over Your Yard

August is the month to try to keep the uber-invasive Japanese stiltgrass from taking over your yard. People familiar with the plant may shake their heads at such a goal, but there are still many yards that are free of its plague-like qualities, whether through luck or a combination of early intervention, vigilance, and persistence.

Have you seen it? There's usually a white line running down the middle of each leaf. It looks harmless, even graceful, but stiltgrass (Microstegium vimineum for long) spreads so aggressively that it can blanket whole forests, or line roadsides for miles. Once you learn to identify it, you may start seeing it everywhere.

Michigan had until recently been spared, but here's my Ann Arbor friend Sam's backyard last year. Another friend, Victorino, who grew up in Guatamala, called it "communista." I had to laugh, if grimly, because replacing diversity and individuality with monocultural conformity and oppression is what stiltgrass does all too well.  It's a warm-season annual grass, meaning that it sprouts from seed late in the spring and matures through the summer. By late August it can grow up and over everything else, then sets zillions of seeds in September.

Because stiltgrass is an annual, the way to fight is to prevent it from successfully producing seed. 

Here's Sam's backyard after he weed-whacked the stiltgrass in July. A lot of work, but maybe effective, because I saw surprisingly little regrowth through all the resultant mulch.

Weedwhacking can also be done in mid to late August, just before the flowers form, to reduce even further the chance of resprouts that could produce seed. Do this year after year, and eventually the soil will run out of seed to sprout.

But by far the best way to keep stiltgrass from taking over is to catch it early. Even though it has blanketed many areas of Princeton, there are still substantial areas that can be saved from its smothering growth by strategic, annual action. This super plant has a big weakness: it has super weak roots, and pulls super easy.

Look closely at this photo. Do you see the stiltgrass mixed in with the other foliage? Pull those few plants, and there will be no stiltgrass to produce seed. Stiltgrass spreads into new areas of nature preserves primarily along trails, so some scouting and strategic pulling in August is an excellent way to protect large portions of preserves from incursion.

Otherwise, the trail can end up looking like in this photo.

It can even grow in a miniature form in mowed lawn.

For homeowners, where there are just too many to pull, another approach is to spot spray with a super dilute formula of systemic herbicide. You can see at the bottom of the photo how tiny the roots are compared to the plant. That's where the herbicide does its work. The Penn State Extension website offers some means of control.

Whatever combination of methods you use, it's best to start early in August. Make one pass through an area, then check back in a week or two to get any that were missed the first time through.

Though many people are intimidated by the thought of distinguishing one grass from another, it's possible to get quite good at it over time. Below are some plants that can be mistaken for stiltgrass.

Carpgrass is another nonnative annual grass, shorter, with wavy leaves, and less common than stiltgrass but similarly invasive. 

Virginia whitegrass (Leersia virginica) is a native with narrower, longer leaves. It flowers earlier and lacks the white stripe down the leaf. As with most native plants, this species "plays well with others," growing here and there without dominating.

I'm calling this one Heller's Rosettegrass, Dichanthelium oligosanthes. It's sometimes recommended for native lawns, but shows up in woods around Princeton.

Various other native Dichantheliums make life interesting. These native grasses tend to be perennials, and so better rooted and more resistant when you accidentally pull at one.

Various smartweeds can also look somewhat like stiltgrass. Smartweeds can be rambunctious, whether native or nonnative. 

Though I've despaired at the sight of stiltgrass rising in late summer like an indomitable sea in some areas, I've also been surprised and gratified to find many areas that remain free of it, and could continue to be if people act strategically year after year. 

Related posts:

Stiltgrass Reaches Michigan

Last Chance to Pull Stiltgrass -- 2023

A Video Tour of the Veblen Circle of Native Wildflowers

Here's a video tour of the circle of wildflowers we planted in honor of Oswald and Elizabeth Veblen, whose generosity and love of nature led to Princeton's first nature preserve, Herrontown Woods.

Most woods are largely silent, flower-wise, in late summer, but in the woodland opening of the Barden, where scattered trees allow sunlight to reach the ground, sun-loving native wildflowers of summer can prosper. The video was shot during a pop-up May's Cafe hosted by the Friends of Herrontown Woods.

The Barden is home to more than 150 species of native trees, shrubs, grasses, and wildflowers 

The PHS Ecolab Wetland Begins its Third Life

They say that cats have nine lives. How many lives can a wetland have? The Princeton High School Ecolab Wetland is now beginning its third. Lush and verdant in June, it was stripped bare of vegetation for the second time in its 17 year history at the beginning of July. The first time this radical change happened, in the fall of 2022, took me and environmental teaching staff completely by surprise. This time, the lines of communication were open, and the reasoning fully understood.

On June 12th, the wetland--a brick-lined detention basin squeezed between the science and performing arts wings of the school on Walnut Street--looked like this. The elderberries were abloomin' along the edges of lush sweeps of sedges, rushes, and wildflowers that thrive in full sun and ground magically kept moist by sump pump water.

There were also cattails, lots of cattails--narrowleaf and broadleaf. Cattails, with their vertical hotdog-shaped stalks raised high, are the iconic wetland plant. But when I see cattails in a wetland that I'm taking care of, my reaction is "oh, oh." You may see cattails being overwhelmed by the tall invasive reed Phragmitis in the ditches along freeways, but in a sunny wetland like the high school Ecolab, cattails themselves can play the bully, spreading aggressively with the thick rhizomes they send out in all directions.

Thus, when I stopped by the Ecolab less than a month later, on July 7, and saw all that lush, beautiful native vegetation stripped bare, I grieved the loss, but I also saw a potential silver lining.

The reason for the transformation was the need to replace two of the basin's walls. The blocks originally used to make the wall had become corroded by salt used to de-ice the adjacent walkways in winter. Replacing the blocks required complete demolition and rebuilding. The large tubes in the photo conveyed the frequent discharges of sump pump water away from the work area. 

During the repair phase, I was in ongoing communication with the contractor, Patrick, and environmental science teacher Jim Smirk. I wanted to make sure that the hydraulic conditions so favorable to diverse wetland plant growth--the combination of some higher ground with a series of three pools to transport the sump pump water slowly towards the drain--would be restored. Though I was out of town on a band tour in Michigan, Patrick was very accommodating and even sent a photo to make sure he had reformed the ground the way we wanted.

It may look like a moonscape, but already some of the old vegetation is beginning to reemerge from whatever roots are still intact. We may need to do some replanting, but after 17 years, the soil should be packed with native seed ready to sprout over the coming year.

Now is a critical time for the Ecolab's future. That first stripping of vegetation in fall 2022 had been prompted by willow trees that had grown too big for the site. As vegetation rebounded, I assiduously removed the sprouts of willows and any other trees with the potential to grow too large. This time, it's the cattails that pose a danger.

What plant species are going to feed off of all that wonderful sun and cool sump pump water from the high school's basement? If we let the cattails reestablish, the Ecolab will eventually become stuffed with cattails and little else. If instead we remove all sprouting cattails and encourage native species that are less aggressive, then it will be much easier to sustain biodiversity over time. As with the growth and development of people, intervention early on in a wetland's rebirth can determine longterm fate. 

Related posts:

A Wet Meadow is Born -- We used a similar strategy of early and ongoing intervention when a detention basin was replanted with native species in Princeton's Smoyer Park 9 years ago. That wet meadow is now thriving, with very few weeds and lots of native diversity.

The Work Behind a Natural-looking Meadow--a more recent post about the Smoyer Park wet meadow.