Elimination of Onion Grass

Onion grass is similar in appearance to cultivated onion plants.

Onion grass is generally not a welcome weed in a lawn. Its dark, green, waxy leaves disrupt the turf, and the strong odor of onion can be smelled after cutting the grass. Like the garden variety, onion grass is edible and looks similar. It tends to be more of a problem in poorly drained lawns and thin turf areas.

Description

Onion grass, or wild onion (Allium canadense), is a winter perennial. It emerges in late fall from underground bulbs and grows throughout the winter and spring. During late spring, bulblets form and the plant dies back. The underground bulbs, however, can persist in the soil for years. Onion grass has thin, green, waxy leaves that are flat and solid.

Pulling

If the amount of onion grass in your lawn is small, hand pulling it is an option. The key to successfully pulling onion grass is to be sure to remove the entire plant. If you don't remove all of the plant, bulbs or bulblets may remain in the ground and new leaves will emerge in the fall. For best results, dig out onion grass with a thin trowel and dig deep beneath the plant to remove it entirely.

Mowing & Fertilizing

While mowing will not kill onion grass, it can weaken the plants and prevent them from setting seed. Control onion grass by maintaining a dense, healthy turf and ensuring proper mowing height and frequency. Fertilize the lawn with emphasis on fall nitrogen. While this may not eliminate the onion grass completely, it will make the weeds less noticeable.

Chemical

There are no pre-emergent herbicides that will control onion grass. The weeds need to be treated with a post-emergent herbicide containing 2,4-D, MCPP, dicamba, clopyralid, or triclopyr. Consult with your county extension office for recommendations. Treat onion grass in the late fall and again in late winter or early spring. Persistence is key; the plants will need to be sprayed more than once. One aspect that makes control difficult is that onion grass has a thin, glossy leaf and herbicides don't readily adhere to it. Mowing the onion immediately before application may improve uptake. After applying the herbicide, do not mow the lawn for at least two weeks.

References

• Clemson University Cooperative Extension; Wild Garlic and Wild Onion; Chuck Burgess; May 2004
• Michigan State University Extension; IPM Wild Onion and Wild Garlic; Fred Salzman, et al.; December 1997
• Purdue Extension; Wild Onions and Wild Garlic -- A Nuisance in Wheat Fields and Lawns; Glenn Nice, et al.; March 2003
• University of Nebraska-Lincoln; Controlling Wild Onion or Wild Garlic; April 2010