What Is Onion Grass and How to Identify It

Onion grass along Tranquility Lane in the Franklin Farm section of Oak Hill, Fairfax County, Virginia

If you’ve just mowed your grass and notice a tear coming to your eye, it may not just be tears of joy from your beautiful lawn. You might have a perennial weed called onion grass. But what is onion grass, and how do you identify it?

In short, onion grass, also called wild garlic, is a weed. An aggressive and invasive weed, at that. This plant is one that you most certainly don’t want in your yard if you’re trying to keep a lush carpet of grass. Thankfully, there are ways you can both keep it out and remove it when it creeps its way in.

Read below to learn more about onion grass and how to protect your lawn from it.

How to Identify Onion Grass

Onion grass in fall
Photo Credit: Famartin / Wikimedia Commons / CC BY-SA 4.0

Identifying onion grass can be a bit tricky if you’re not sure what to look for. Thankfully, once you do, you should be able to spot this weed no problem.

Firstly, onion grass is thicker and sometimes grows taller than most lawn grasses, so look for especially thick or tall patches of grass. Second, you may be able to notice the top of the bulb peeking out from the soil, which is a great help when you’re looking for onion grass.

Another good way to identify onion grass is by its smell. Just as you would think, onion grass has a distinct smell of onions. This smell should be especially noticeable after the plant is cut. After cutting your grass, take a lap around your yard and see if you can smell onions. If you can, there’s likely some onion grass nearby.

Onion grass grows from late fall to early spring, so you’re most likely to see it sprout up then. However, remember that onion grass is a perennial, which means that it grows back every year. In addition, the main part of the plant grows underground, so it’s easy to miss. Both of these combined can make onion grass a very stubborn plant.

For more information on identifying weeds, read this article: Read Your Weeds: Identify Them to Learn About Your Lawn’s Health.

Why Onion Grass is a Problem

Like most weeds, onion grass is an unsightly intruder in your lawn. 

Onion Grass is not native to the United States. It originally came from Europe, Africa, and the Middle East and has become an invasive species in the U.S. An ‘invasive species’ is any non-native animal or plant that harms the environment it’s introduced into, usually by outcompeting the local species or killing them outright. In this case, that ‘local species’ is your lawn.

Onion grass will take over patches of grass and can even overtake your entire lawn if left unchecked. This species spreads rapidly once it’s established and can require multiple seasons to get rid of. For the sake of your lawn, remove onion grass as soon as you identify it.

How to Remove Onion Grass

Getting rid of onion grass for good isn’t easy, but it is possible. There are two main methods for removing this weed: removing the plant by hand or killing it with herbicides. Here are some details on both methods.

Removing Onion Grass By Hand

The first, and best, way to get rid of onion grass is to pull it right out of the ground. Dig it up, bulb and all, in one big clump, and throw it straight in the garbage. If you’ve done it right, there should be no part of the plant left in the ground. Afterward, you can fill in the empty space with new soil and grass seed.

This method ensures that there’s nothing left behind for the onion grass to grow back from. It also ensures that there are no seeds left behind to take root and start the process over again. It’s quite effective at removing small patches of onion grass, but unfortunately, it’s not much use when you have a large area of it in your lawn.

Removing Onion Grass With Chemicals

Your other option is an herbicide. This should be your last resort should all other methods fail. The reason for this is that most herbicides will be ineffective against onion grass. You need one with glyphosate, which is a non-targeting herbicide. Non-targeting means that the weed killer will also kill your grass.

If you do choose a glyphosate herbicide, use flattened cardboard to cover the border of the area the onion grass is in so that you can minimize the damage to your lawn. Apply the herbicide and ensure you follow the instructions in order to do it properly.

Once the onion grass is dead, mow that entire area of the lawn as short as you can. Next, reseed the grass or lay down new sod to fill in the area and regrow the turf.

To learn more about herbicides, read this article on Types of Post-Emergent Herbicides. For general weed control tips, read this one about How to Get Rid of Stubborn Weeds In Your Grass.

How to Prevent Onion Grass

Onion grass (Allium vineale) early spring
Photo Credit: User:SB_Johnny / Wikimedia Commons / CC BY-SA 3.0

Thankfully, you can prevent onion grass from cropping up in your yard as long as you stay vigilant. Monitor your lawn closely and identify and remove onion grass whenever it appears.

You should also prevent onion grass by making your yard inhospitable to it. Here’s a short list of things you can do to discourage onion grass in your yard:

  • Maintain Your Lawn: A healthy lawn makes for a bad growing environment for weeds like onion grass. Keep your lawn in good shape so that it’s strong enough to outcompete onion grass.
  • Keep Thick Grass: Onion grass doesn’t grow well in thick grass. If you have a thick lawn, it will have an easier time repelling onion grass.
  • Raise Your Soil pH: Onion grass prefers acidic soil. Keep the pH at a neutral or basic level to create an inhospitable environment for onion grass.
  • Aerate Your Soil: Onion grass grows well in heavy, compacted soil. Aerating your soil on a regular basis will help prevent onion grass from growing. Read this guide to learn about What to Do After Aerating Your Lawn.
  • Add Compost: Lastly, adding compost and topsoil to your lawn will help prevent onion grass. Onion grass prefers soil with a low nutrient count, so adding nutrients will help prevent it from growing.

Where Does Onion Grass Come From?

Onion grass in lawn
Photo Credit: Famartin / Wikimedia Commons / CC BY-SA 4.0

If you have onion grass cropping up in your yard, you may be wondering where it came from. Weeds can come from almost anywhere. Onion grass in particular can lie in wait for quite some time. Their underground bulbs can go dormant for up to six years, so it could have been there for ages and you just never knew. 

Of course, every plant needs to spread somehow, and onion grass is no different. Here’s a couple of ways onion grass can spread to your lawn:

Spreading Through Birds

A common way that weeds like onion grass spread is through birds. Birds eat plants’ seeds, then leave droppings with those seeds just about everywhere, including your lawn. Feathered friends like sparrows and robins may be a welcome sight in a suburban landscape, but they unfortunately can also spread weeds.

Spreading From Other Lawns

Alternatively, if your neighbor has onion grass in their lawn, it can spread to yours if it goes unaddressed.

This usually requires the onion grass to be present for a long time and, depending on where in the other lawn it started, to overtake quite a bit of the initial lawn, so it’s rather unlikely that it will go unnoticed for such a long period of time. However, it’s not impossible.

FAQ About Onion Grass

Sort of. Onions and onion grass are both members of the genus Allium. Common onions that we eat and buy in a grocery store are Allium cepa, while onion grass is Allium vineale. Think of them as distant cousins.

Is onion grass edible?

Yes. The leaves, flowers, and bulbs of the onion grass plant are all edible. If you’d like, you can try to grow it in a food garden.

If you pull onion grass out of your yard, though, and want to try chowing down on it, you should reconsider if you treat your lawn with pesticides. Even if onion grass is resistant to them or if you haven’t targeted it with poisons, you still don’t want to roll those dice.

Why does onion grass keep coming back?

If you have a recurring onion grass problem, it’s likely because you’re only removing the surface part of the plant. Just like the veggie they’re named after, onion grass grows bulbs below the ground. That’s what you need to remove in order to get rid of onion grass for good. If it’s still present, the plant will keep coming back every year.

Find Your Lawn Expert

Onion grass might be annoying, but you can keep it out of your lawn if you stay vigilant. When it arrives, get rid of it immediately to protect your grass.

If you need expert help with your grass, contact lawn care professionals near you. They can take care of your yard, mow the turf, and protect your lawn from invasive weeds.

Main Photo Credit: Famartin / Wikimedia Commons / CC BY-SA 4.0

Austin Geiger

Austin Geiger

Austin Geiger is a lover of all things nature. He enjoys writing comprehensive, easy-to-swallow articles about pest management solutions, landscaping tips, and ways for people to help their local pollinators.