what is onion grass

What Is Onion Grass (Allium vineale) & How To Get Rid Of It

In Lawn & Garden by Jamie

Have you ever mowed your lawn and caught the unmistakable scent of onions? Or seen chive-like leaves poking out of your lawn? You’ve got Allium vineale, also known as onion grass.

Onion grass refers to Allium vineale, a wild chives-like edible perennial that can pop up in lawns. As it grows from a bulb, it’s mainly spotted in spring and fall before the leaves die off to survive hot and cold temperatures. Onion grass also refers to Romulea rosea, an herbaceous perennial with purple flowers that’s an environmental weed in Australia.

What Causes Onion Grass?

Allium vineale establishes itself through seeds. Once the seeds sprout, they grow bulbs which store up energy through the cool-season to allow the plant to withstand hot temperatures in the summer and freezing temperatures during the winter. The visible leaves die off in the fall and sprout again come spring. This process can make it look as if the onion grass sprouted up in the fall or spring, but it’s been there the whole time.

Encouraging thick, healthy grass is your best defense against onion grass, as, like other unwanted plants, their seeds take advantage of open soil with access to light. Core aerating a lawn and overseeding each year will help thicken up your grass, as will letting it grow longer (shading out soil) and applying compost and compost tea to encourage vigorous growth.

Onion grass may indicate low calcium, low organic matter content, high potassium, and/or poor drainage in the soil. As always, get a soil test done before adding any amendments.

How Do You Get Rid of Onion Grass?

Outside of displacing grass and sticking out unsightly, onion grass doesn’t harm a lawn. However, if not properly controlled, they can spread quickly. Once spread, effectively removing onion grass may take a few years.

Mow regularly to prevent onion grass from going to seed. While onion grass returns each year by storing its energy in a bulb, it spreads through seeds. By keeping onion grass leaves’ short, the plant will put all its energy into developing leaves instead of seeds. Mowing also helps prevent the roots from lengthening and growing more established.

Remove the entire bulb. So long as any part of the bulb remains, onion grass can regrow. Removing the leaves won’t get rid of it either. So if you’re going to try removing it physically, dig carefully and give it a wide berth so you can remove the whole bulb. Reseed the bare earth. Do not rototill as this will just worsen your onion grass problem.

Pour boiling water. Scalding hot water will kill just about any plant, from onion grass to turfgrass. This can be an effective natural weedkiller, although it’ll also kill everything around it. Use only when dealing with big clumps.

Target with specific herbicide after mowing. Herbicide use should be used as a last resort, as even lawn-safe herbicides can stress your grass out to the point of harm, as well as harm the environment and people and pets who come into contact with it. Herbicide use is also not very effective because the leaf shape makes it difficult to apply. If you do resort to herbicides, Paraquat and Imazaquin are the two most effective herbicides. Apply after mowing when the stalks are cut and exposed. And don’t harvest it after!

Can I Mow Onion Grass?

Yes, you can mow onion grass. In fact, regular mowing will help keep it from flowering and spreading throughout your lawn. Mowed onion grass will smell like onions.

Can You Eat Onion Grass?

Yes, like its Allium cousins onions and chives, you can safely eat onion grass either cooked or raw. They taste stronger than their domesticated cousins. However, some lookalikes are poisonous (like the aptly named Crow Poison and Death Camas), so make sure you positively identify it as onion grass before eating.

To identify edible onion grass, check that it:

  • Smells like onions.
  • Leaves look like blades of grass with a slightly curved U shape. (Don’t rely solely on leaf shape, as Death Camas can look pretty similar, just less succulent.)
  • Grows from a bulb. (The bulb is round and small, or long and stem-like.)
  • Blossoms with white, six-petal flowers.

Also, avoid harvesting onion grass that’s been chemically fertilized or sprayed with pesticides or herbicides.

Is Onion Grass Toxic To Animals?

The Allium genus, including onion grass, is toxic to dogs, cats, and horses when ingested. Most common cases of onion poisoning are caused by domestic onions, though, and animals need to eat a large quantity to cause severe anemia or eat it in small quantities over time. Keep pets away from it, as they may try to nibble it like it’s grass.

If you know your dog, cat, or horse ate onions, contact a vet right away. If you’re not certain, but they exhibit symptoms like weakness, onion-smelling breath, bloody urine, and more (complete symptoms for dogs, cats, and horses), take your pet to the vet.

Final Thoughts

Allium vineale is a common lawn weed that’s perennial and can spread quickly. While it’s safe for humans to eat, it’s toxic to animals. Control it by keeping a thick lawn that makes it difficult for seeds to take root and by keeping it cut short to prevent it from seeding. If it’s taking over your lawn, then you may need to resort to digging them up (keeping the bulb in one piece), or pouring boiling water over them. A few herbicides can be effective, but their leaf shape makes them naturally resistant.