How to Kill Onion Grass

Wild onion (Allium canadense) is a weed with flat leaves. It is also known as onion grass. This weed is a perennial plant and therefore needs multi-season treatments to get rid of it. Its underground bulbs persist for years. The grass emerges from the bulbs in the late fall and grows through the spring. Since they grow in tight patches, it is tempting to just pull it up, but this can leave the underground bulbs quite viable. Fortunately, selective pesticides exist for its treatment.

Things You'll Need

• Herbicide
• Trowel

Instructions

1. Prevent growth of onion grass in the garden with a thick layer of mulch.

2. Dig up small infestations with a trowel, digging under the bulbs. Fortunately, the roots don't extend much below the bulb, which themselves are shallow.

3. Use any of the following as selective herbicides: imazaquin (Image brand), metsulfuron methyl (Manor brand), imazapic (Plateau brand), or 2,4-D. Follow the directions on the container for the amount to apply. "Selective" means that they will kill the wild onion but not your grass.

4. Repeat the application over multiple seasons, since the plant is perennial. Once in the late fall and once in the late winter is best. The fall application gets sucked into the roots, and the late winter application prevents bulb growth just before spring.

5. Fertilize your lawn with nitrogen in the fall to help your lawn out-compete the wild onion.

Tips & Warnings

• See the Purdue website below to see how to control wild onion in wheat crop.

• Don't remove wild onion by hand, since it tends to break off at the stem. Use the trowel method instead.

• Since these herbicides could degrade grass seeds, wait a month after application before seeding a lawn.

References

• U. of Ga. Cooperative Extension Service: Wild Onions and Wild Garlic
• Clemson U. Extension: Wild Garlic and Wild Onion
• Purdue U.: Wild Onions and Wild Garlic -- A Nuisance in Wheat Fields and Lawns