How to take care of pesky Japanese stiltgrass, without fire and fury

“May I set my lawn on fire?”

Josh in Annapolis, Maryland, writes: “I would like to start my lawn from scratch this coming fall. It’s been taken over by invasive Japanese stiltgrass. I was hoping I could burn the whole lawn in August and replant in September but I hesitate because it’s dry that time of year and fire can have a tendency to get out of control.”

Almost certainly illegal, this plan is also foolish, Josh. We’re not talking sagebrush here; grasses are 90 percent water — you’ll never keep them lit!

Drown those weeds instead!

But you might be able to succeed by taking the opposite tack. Stiltgrass is very shallow rooted; if you gather up some help, saturate the area with water and host a “pulling party” the slitgrass plants should come out of the lawn easily, roots and all.

“Some say these weeds will end in fire …”

Josh in Annapolis’ plan to set his lawn on fire to fight Japanese stiltgrass sounds dangerous, ineffective and downright illegal. Luckily, he also writes: “Or is there another natural way to do this?”

Well, first, you’re correct to start in the fall, Josh; that’s the perfect planting time for new cool-season lawns in our area. And you can still use fire to prepare.

Japanese stiltgrass is an annual plant, not a perennial. It depends on seeds dropped in the fall to survive year to year (just like crab grass). So let the plants grow taller than normal and torch the tops of the stiltgrass with a flame weeder in August to destroy those seeds. Then you can just pull out the dead stiltgrass clumps and overseed the lawn instead of starting over.

Solar-powered smothering

Josh in Annapolis has another idea. He writes: “I’m also thinking about laying down cardboard or newspaper covered with compost early in the season to kill everything and then reseed in the fall. How I should go about doing this?”

The correct way, Josh. Instead of hoping to smother, insure the death of the old turf with proper soil solarization.

  • Scalp the lawn down as low as possible this spring; you want to see dirt blow out the back of the mower.
  • Saturate the flattened area with water; more than you think you can possibly need.
  • Then stretch clear plastic (2 mil is ideal) overtop and anchor the edges down well.
  • Leave the plastic in place all summer and no weeds or their seeds will survive.

(You’ll find lots more details and links about soil solarization in this article Mike penned for his Public Radio show some years back.)

Stiltgrass? Start with unsoaking the soil

Invasive Japanese stiltgrass is a scourge of so many local lawns because it thrives in the kind of moist, shady conditions that prevent success with turfgrass. That’s why longterm control involves improving the soil more than mounting a direct attack.

If the lawn drains poorly, plan to have a core aeration performed at the end of August. By pulling plugs of soil and sod out of the lawn with a giant machine, you reduce the compaction that causes wanted grasses to struggle and weeds to thrive.

Then pulling out the existing stiltgrass from soaked soil followed by some fresh seed may be all you need to do.

Shady lawns need seed!

Like many of you, Josh in Annapolis is battling invasive Japanese stiltgrass — a weed that looks tough but actually pulls easily out of soaking wet soil. How has this relatively weak weed become the scourge of local lawns? Because it thrives in the kind of moist, shady conditions that make turfgrass struggle.

Core aeration in the fall can improve your lawn’s drainage, but shade is a tougher issue. There are grasses — specifically fine fescues — that can survive with the least amount of sun, but they can’t handle foot traffic. And no type of fescue can spread, so you need to overseed every season or so.

But do that — improve the drainage and spread fresh seed in the fall — and you just might stiff the stiltgrass. (Just make sure the new seed matches the old lawn or it’ll look like a patchwork of weeds!)

Meet Mike in Fredericksburg in March

Mike will appear Saturday, March 17 at noon and 3 p.m. and Sunday, March 18 at noon and 2 p.m. at the Fredericksburg Home & Flower Show at the Expo Center in Fredericksburg.

Mike McGrath was Editor-in-Chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated Public Radio show “You Bet Your Garden” since 1998 and Garden Editor for WTOP since 1999. Send him your garden or pest control questions at

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