It’s thin and tall and almost never comes out by the root, instead breaking off just below the soil surface and releasing a pungent oniony odor that lingers on your hand—onion grass. Tufts of onion grass grow taller than the rest of the lawn, and strands of it poke up through the mulch in flower beds and vegetable gardens, seemingly mocking you with their refusal to come cleanly out of the soil. If you have a lot of it, you might begin despairing over how to get rid of onion grass. This pesky weed doesn’t carpet the ground like some, but it can feel impossible to control.
Instead, think about the rare but blissful satisfaction of tugging on one of those leaf blades and having it slip free of the loose soil, the white bulb dangling at the end. Onion grass can be controlled, and the methods to remove it might be simpler than you think. With a bit of patience and persistence, you can minimize and maybe even eradicate the onion grass population in your garden.
What is Onion Grass?
But wait, what is onion grass? Grass has fibrous roots and thin, flat leaf blades, so that word doesn’t seem to apply. Onion is closer, but still not quite right. In fact, the plant we most commonly call “onion grass” is wild garlic (Allium vineale). Wild garlic has tiny white bulbs, each with a single round, hollow leaf that emits a strong onion odor when broken or crushed. This nonnative winter perennial emerges in late fall or early spring and grows through the colder months, producing a globe of aerial bulblets in late spring or early summer and then dying back.
If your onion grass has flat rather than round leaves, it might be wild onion (A. canadense), a similar but native allium. In contrast to wild garlic, wild onion produces multiple flat, solid leaves from a single bulb. It also has terminal clusters of white to pink, star-shaped flowers in late spring to early summer.
Regardless of which species of onion grass causes you grief, the control methods are the same.
How to Get Rid of Onion Grass
The best way to get rid of onion grass will depend on how much you’re dealing with and where it’s growing. For example, a small amount in a flower bed can be easily hand-dug, while numerous patches in the yard might be more easily drowned, sprayed, or simply mowed.
1. Dig it up
Usually, digging onion grass out by hand is the most effective method. This ensures that the entire plant, bulb, and all are removed from the soil, eliminating chances of it coming back. To make the job easier, dig when the soil is moist and looser. When digging out clumps of onion grass, do your best to remove all the tiny bulbs. Some might get missed anyway and need to be dug up later.
Hand pulling usually leaves many more bulbs behind, as the foliage breaks easily, though it can be effective in loose, loamy, moist soil. For large infestations in the vegetable garden, fall tillage helps reduce onion grass germination.
2. Mow it
While mowing does not kill onion grass, regular mowing will weaken the plants and prevent them from forming bulblets and spreading. Onion grass does not truly cause any harm to the lawn, so you may choose to simply live with it and control it with your usual mowing schedule.
If you find it troublesome, though, and have significant amounts of onion grass, try breaking up the work by dividing the yard into sections and treating it one at a time. Dig, drown, or spray the onion grass in one manageable section of the yard, allowing your regular mowing to control the rest until you have time to deal with it. This makes the situation feel less overwhelming, and eventually, you will have an onion-grass-free lawn.
3. Drown it
Try “drowning” the onion grass with vinegar or boiling water for a nontoxic approach that doesn’t require digging. Simply soak the plant with a good dose of vinegar so it penetrates to the bulbs, or pour some boiling water over top of it. Of course, this will kill any immediately surrounding vegetation, but so will pesticides.
Regular white vinegar from your kitchen cabinet will do, or you can purchase vinegar with a higher acidity, often sold for household cleaning purposes. Just use caution when applying vinegar with higher than 10 percent acidity, as it can burn your skin and eyes.
4. Spray it
Herbicides might actually be the least effective method for removing onion grass. The extremely narrow leaves make spraying difficult, and to further complicate matters, they have a thin, waxy coating that prevents herbicides from sticking and penetrating. Plus, the bulbs deep in the soil help the plant recover from any herbicide damage. As with vinegar and boiling water, herbicides will also damage nearby vegetation. Pre-emergent herbicides do not work on onion grass.
For the greatest chance at success, apply herbicide to onion grass in the fall or early spring, after it has sprouted but before it has flowered or produced bulblets. Mow immediately before spraying to expose the inside of the onion grass, then do not mow again for at least two weeks after application. You will likely need to reapply herbicide at least once to eradicate onion grass completely. Always follow the package instructions.
Is Onion Grass Edible?
Both wild garlic and wild onion are edible and may be used like chives or scallions. However, they tend to be tougher, and there are better alliums — both wild and cultivated — to eat. Always make sure to positively identify edible plants before eating them, and do not harvest any that might have been sprayed with herbicide or other toxic chemicals. In western North America, onion grass has an extremely poisonous lookalike called death Camus (Toxicoscordion venenosum).
Pesky, pungent onion grass takes a bit of patience and persistence to eradicate, but the methods for controlling it are actually quite simple and effective. Good luck, and happy gardening!
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Serena Manickam is a freelance editor and writer and sustainable market gardener in rural Virginia. She holds a BA in environmental science and runs Fairydiddle Farm, a small market garden in which she grows no-spray produce and herbs to sell at a local farmer’s market.