Invasive stiltgrass and how to fight it - BlueStone Press
April 19, 2019
Micro-local: State of Nature

Invasive stiltgrass and how to fight it


You might not notice it in the spring or early summer. It’s soft and delicate-looking, but by the end of the summer it is growing as thickly as green hair. Once it appears – on your lawn, in a meadow, a wetland, a forest, an empty lot, a construction site – it is never going to leave without a fight, and will gradually displace every other grass, fern or flower.

That is the nature of Japanese stiltgrass, native to much of Asia. It first arrived in the Tennessee-Kentucky area “probably in the 1920s-1930s as packing material for dishware,” according to Diane Greenberg, co-owner of the Catskill Native Nursery in Kerhonkson. “Unfortunately, the seed came in along with it, and it’s been spreading around ever since.”

An intimate awareness of local plant ecology is part of Greenberg’s job description.

“Plants become invasive if they have not evolved in an ecosystem with checks and balances,” Greenberg explained. In its native environment, “maybe a beetle eats them, or a fungus kills them off if they get too dense. But when a new species just pops in out of the blue, basically it can just run rampant. Invasives actually damage the ecosystem,” she went on. “There’s another term, ‘naturalized,’ for aliens that don't do harm and manage to coexist with other things. Queen Anne’s lace is a classic example. Stiltgrass is a true invasive and a very big problem for our environment. It really doesn’t have any beneficial qualities.”

Stiltgrass gets an unfair advantage over native competition because its seeds are alleopathic – “they're poisonous to other plants. They prevent the germination and growth of other plants. Mustards have this property – it’s why garlic mustard is a problem.” Moreover, “when stiltgrass dies, it falls down on on top of itself and creates a very thick mat – so thick that other plants can't push through it. Eventually you have a monoculture. Where before you might have had 15 or 20 species, suddenly all you have is stiltgrass. It’s really bad down South because it started down there; in fact, in the national parks there are just huge swaths of it. It’s destroyed bogs, it’s destroyed wilderness.”

How did Ulster County become overrun with this stuff?

“A lot of it ended up coming here during the housing boom, because they were so desperate to get soil that they were getting it from areas outside of Ulster County that had stiltgrass. People didn’t know what it was when it showed up here 10 years ago,” Greenberg said. “We even had a case of a woman deliberately putting it on her property because she thought it was some kind of ground cover!” Greenberg warned, “This plant moves around through fill that is not properly solarized. Clean fill is not necessarily seed-free. It just means there are no chemicals in it.”

Stiltgrass gains easy entry on disturbed ground.

“We mostly are finding it on new construction, new homes, and properties where there has been logging,” Greenberg said. “It loves to embed itself in those deep, deep grooves” that you see on truck tires, “especially logging trucks that are always going through wasteland with stilt on it. The truck rolls onto your property, some of it falls off – the next thing you know you’ve got a little patch of stilt, then it becomes a big patch of stilt.

“We did landscape restoration on a really beautiful bog about 10-12 years ago. Then a neighbor did some construction, and four or five years ago all this stiltgrass showed up on the neighbor’s property and marched right into the bog. I have yet to see a new-construction house that does not have stiltgrass. I don’t see it at older homes, unless they have had lumber work.” It’s also often seen along the roadside, “because it’s bouncing off the tires. It doesn’t need good soil, it doesn’t need a lot of light. It can grow in moist conditions, it can grow in dry,” she said.

Greenberg observes the local landscape changing. “I do see it moving around and getting worse. I was just up at Sam’s Point, and we noticed it moving in there … it’s not up into the park yet, it’s by the driveway. Odds are it came in on the fire trucks” sent to put out large blazes in the park in 2016.

“I don't know what's going to happen in the long run, because it really does change ecosystems,” Greenberg said. “If it’s around milkweed long enough, it suffocates the milkweed. We’ve noticed certain populations of bees disappear where it used to be a very diverse meadow that’s become just stiltgrass. We’ve noticed fewer salamanders in woodlands where it takes over. The mushrooms just disappear. I've noticed an area in the woods that always makes chanterelles, and about five years ago stilt showed up, and the area that’s really dense with stilt never has chanterelles any more.”

What can be done?

Getting rid of it is tricky – timing is everything. “If you weed-whack it too early, it’ll just set seed at the bottom,” Greenberg advised. August is the best time to whack it down, “but you want to do it as low as possible, practically on the ground. If you weed-whack it low enough, the plant actually dries out and cannot continue to grow or produce seed.” Or just rip it out. “It’s very easy to pull up when it’s tall enough, so it’s easy to get ahold of, and it hasn't gone to seed yet. You have a three- or four-week window when it’s too late for stiltgrass to germinate and create seed again. It actually looks a little late going to seed this year, but by September most grasses have gone to seed or are at least in flower.”

What can we do now that it’s already September?

“Definitely pulling it up is the best thing,” Greenberg answered. “If you can pull it up before it has any seeds, you can just throw it in the compost pile. If it has seed on it you have to put it in a plastic bag. That is usually the best solution if you don’t have too much of it. But if you miss just one year,” she said with the battle-weary air of long experience, “you’re back to ground zero with tons of it,” because the seeds already in the ground can germinate for two or three years. “There is a native fungus that appears in our soil that does kill it. The problem is, this fungus also kills native grasses.” Greenberg suggested, “Lawn fertilizer will make for a denser lawn, which makes it harder for the stiltgrass to reproduce – just the standard stuff you buy in a hardware store.”

Greenberg rules out weed killers for the obvious reason that they kill the good with the bad, and also will probably fail. “Everyone wants a magic formula, but even Roundup doesn’t work that well on it,” she said.

If your patch of stiltgrass is confined to a particular place, you can try covering it with black plastic, which will kill everything under it if left there long enough (about six weeks, while the weather is warm). Or, “you can mulch it out – the seed cannot germinate in 4 inches of mulch. It’s always something, huh?” Greenberg said. “The world is changing a little faster than we would like it to.”

For more information on stiltgrass, including what native plants to use to replace it, visit:


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