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Dec 23, 2023

Help for Gardeners: Japanese Stiltgrass is hard to control

Fran Kittek / Morning Call File Photo Photo from mdinvasivesp.org, Louisa Thompson, Maryland Native Plant Society Japanese Stiltgrass, a terrestrial plant, grows and expands in various habitats. It is

Fran Kittek / Morning Call File Photo

Photo from mdinvasivesp.org, Louisa Thompson, Maryland Native Plant Society

Japanese Stiltgrass, a terrestrial plant, grows and expands in various habitats. It is shade-tolerant and can cover extensive areas. It threatens native plants by displacing them, covering them (with shade) and changing soil chemistry.

FRAN KITTEK / SPECIAL TO THE MORNING CALL

Japanese stiltgrass, while easily pulled out, reseeds so easily that it is quickly becoming a major problem in local gardens.

For a number of years, my husband and I have been trying to control Japanese Stiltgrass in our lawn. I hate it. It tends to grow very densely and I don’t like the way it looks. More importantly, it is extremely invasive, spreading into wild areas and choking out native plants. We try not to use chemicals, though we have applied a pre-emergent in the past. It seems chemicals are the only way to control it because we’ve found it impossible to pull all of the stiltgrass out of our lawn. We’ve been overseeding with lawn grass seed and we fertilize with an organic lawn fertilizer. This year, we thought the lawn looked better, until recently when the stiltgrass quickly grew and spread. So, I referred to the following Penn State article:

https://extension.psu.edu/controlling-japanese-stiltgrass-in-your-garden

While the article mentions pulling the stiltgrass to prevent seed production, it doesn’t suggest any type of tool that might help with this task. I’ve considered purchasing a powered dethatcher, but I’m not convinced that would work. Do you know whether or not it would? We’ve tried a manual detaching rake. Beside the fact that it’s physically difficult to use, the sharp metal tines tend to cut the stems, so it doesn’t remove all of the stiltgrass. Can you suggest a tool that is (hopefully) a little easier to use, but is more effective for pulling up the mats of stiltgrass in our lawn? Thank you.

— Anna Grunwald

The Penn State article is quite thorough. Japanese Stiltgrass (Microstegium vimineum) is a very invasive and difficult to control weed. The grass grows one foot to three-feet tall and produces spreading mat. Although it is an annual, it can produce thick mats of thatch that will smother other competing vegetation. The leaves, arranged alternately on the branched stake, are about one inch to three inches long and bright green. There is a silvery strip on the midrib of each leaf. The flowers appear at the top of the stalks and set seed in late August to September.

There is no hope of eradicating it. Control will take a multipronged approach. Anne has applied several of the control methods, but will need to employ them all in the same season. Japanese stiltgrass seeds quite freely and readily grows in most areas. The seeds, small, shiny and sticky, are spread throughout the landscape on the fur and hooves of animals, flowing or flooding water, and on the clothes and shoes of anyone who comes in contact with them.

Control stiltgrass spread by mulching ornamental beds and maintaining dense, healthy lawn. Avoid cutting grass very low, as it stresses the grass, and any bare spot or sparsely grassed location is a potential site for stiltgrass to grow.

Hand-pulling is a good control for small patches. The grass is shallow-rooted and easily removed. Remember that since this opportunistic weed grows well in disturbed soil, areas recently weeded will have a regrowth, as seeds already in the soil are stimulated to germinate. Large patches should be mown in August after the flowers have appeared, but before the seeds are mature. Ideally, bag and dispose of clippings. Cutting earlier in the season will result in shortened plants that still develop seeds. Note that plants, particularly mature ones, should not be composted.

Pre-emergent herbicides are of some use, but will only kill those seeds that germinate that season. Note that stiltgrass germinates several weeks before crabgrass, so any herbicide should be timed to that event. Seeds are viable in the soil for several years (about five). Post-emergent herbicides are effective, but generally non-discriminative, killing whatever they touch, and are environmentally damaging in many cases.

As far as dethatching, I would not worry if the roots are not removed, as the grass is an annual and will die off at the end of the season. Dethatching will help remove the dense mats that develop in heavy infestations, but if the plants have matured, it will also disperse the 100 to 1,000 seeds that each plant can produce. Dethatching will also disturb the soil and, as previously mentioned, result in a new crop of weeds from previously dormant seeds in the soil.

Control must employ several methods. Cutting before seeds mature, mulching beds, dethatching will combine to decrease the number of plants. However, no method or combination of methods will be effective unless it/they are employed annually.

Another descriptive and informative site is: https://extension.umd.edu/hgic/topics/japanese-stiltgrass, from the University of Maryland Extension website.

Sue Kittek is a freelance garden columnist, writer, and lecturer. Send questions to Garden Keeper at [email protected] or mail: Garden Keeper, The Morning Call, PO Box 1260, Allentown, PA 18105.

Week in the Garden

Planting

Sow seeds for fall flowers and foliage: pansies, snapdragons, mustard, cabbage and kale.

Plant but protect from heat: late-season cabbage, carrots, cauliflower, peas, and broccoli for late summer or early fall harvest.

Also sow seeds that require a cold period for germination; poppies are one example.

Purchase asters and mums for your fall display, either in the garden or as part of a container display.

Hold new plants until the weather cools.

Gather pots together to make watering easier.

Seasonal

Stake tall flowers and provide supports for vining plants.

Allow the final flush of flowers to go to seed. Many provide food for the birds and small mammals during the fall and winter.

Take cuttings of those annuals that you want to winter over, or other favorite plants that have grown too big to move indoors.

Order asparagus, rhubarb, bulbs, flower and fruit plants, and shrubs for fall planting.

Shop nurseries for end-of-season bargains or new fall arrivals.

Weed often and cut off flowers of any weeds you don’t get pulled out.

Deadhead flowers and trim damaged, diseased, and dead foliage to keep beds tidy and encourage reblooming. In particular, keep irises and daylilies from forming seedpods.

Allow peony greens to grow until fall and then cut back.

Prune summer-flowering shrubs about two weeks after flowering.

Apply corn gluten-based weed control in the garden and establish a schedule for reapplication, usually at four- to six-week intervals.

Lawn

Purchase seed for fall lawn projects and broadleaf weed control.

Plan sodding projects and order sod for early fall installation.

Treat for chinch bugs and sod webworms.

Purchase fertilizer and, if desired, apply now until mid-October.

Cut as needed, based on growth, not schedule, to a height of about 2 1/2 to 3 inches tall. Use a sharp blade.

Keep newly seeded or sodded lawns watered; supplement rain in weeks where less than an inch.

Apply pre-emergent crabgrass control.

Fill in holes and low spots in lawn.

Apply corn gluten based-weed control in the garden; reapply at four- to six-week intervals.

Chores

Start planning for fall. Order bulb and plants for early fall shipment.

Start getting plants ready to bring in. Repot those that need it and pot up those you want to winter over indoors

Harvest crops regularly, at least every other day.

Check hoses; replace washers and correct leaky connections.

Dump standing water and remove anything that may collect rainwater to help control mosquito populations.

Check seed inventory for late crops and fall planting.

Water any recent plantings and containers anytime we experience a week with less than an inch of rain.

Fix damaged screens and garden hoses.

Note damaged caulking around doors and windows.

Dump standing water and remove anything that may collect rainwater to help control mosquito populations.

Provide deer, rabbit and groundhog protection for vulnerable plants. Reapply taste or scent deterrents.

Clean and fill bird feeders regularly. Clean up spilled seed and empty hulls.

Dump, scrub and refill birdbaths at least once a week.

Consider setting out nesting materials if you have them.

Clear gutters and direct rainwater runoff away from house foundations.

Tools, equipment, and supplies

Check and store winter/fall equipment, repair or replace as needed.

Safety

Clear lawns of debris before mowing and make sure pets, children and others are well away from the area being mown.

Store garden chemicals indoors away from pets and children. Discard outdated ones at local chemical collection events.

Photograph storm damage before clearing or repairing for insurance claims and file promptly.

Anytime you are outside and the temperatures are about 50 degrees F or warmer, watch for tick bites.

Use an insect repellent containing Deet on the skin.

Apply a permethrin product to clothing.

Wear light-colored clothing, long sleeves, hats and long pants when working in the garden.

Stay hydrated. Drink water or other non-caffeinated, nonalcoholic beverages.

Even in cold weather, apply sunscreen, wear hats and limit exposure to sun.

Wear closed-toe shoes and gloves; use eye protection; and use ear protection when using any loud power tools.

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