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Australian Guide to Getting Rid of Onion Weed

Onion weed is one of the most frustrating backyard weeds in Australia.

Featured Image: Allium triquetrum I Photo by Ewen Cameron (cropped) I Auckland Museum, Wikimedia I CC BY 4.0

One Onion Weed plant can spread across a large area quickly and it is far from simple to completely eradicate it.

Looking to get your onion weed problem under control?

Below, we outline the main methods for getting rid of this pesky weed.

What is onion weed?

Allium triquetrum 2 | Weed control
Allium triquetrum I Photo by Ewen Cameron (cropped) I Auckland Museum, Wikimedia I CC BY 4.0

Onion weed (also known as Allium triquetrum, Asphodelus fistulosus and Nothoscordum inodorum), is a flowering plant with thin green leaves and a white bulb containing bulblets that grow into new plants.

These mini bulbs continue to grow even after the original plant has been killed, which can make it extremely difficult to get rid of completely.

It readily reproduces by seeds that travel through the soil and by wind and water.

Onion weeds are usually found in lawns where they are considered an invasive species because of their ability to spread rapidly.

How to spray onion weed with herbicide

Asphodelus fistulosus | Weed control
Asphodelus fistulosus I Photo by Harry Rose I Flickr I CC BY 2.0

Common lawn weeds in Australia can be grouped into two different categories, broadleaf and grassy weeds.

Broadleaf weeds include Bindii, Clover, and Dandelion. These weeds can be treated with selective herbicides.

However, onion weed is considered a grassy weed.

These are somewhat harder to control because a broadleaf herbicide will not work on them.

Pre-emergent herbicides

One option for killing grassy weeds is to use a pre-emergent herbicide in late winter.

These types of weed killers will prevent the weed seeds from germinating in the first place.

They effectively form a barrier on the surface of the soil so no new weeds can grow. 

Glyphosate

A herbicide containing glyphosate is considered the most effective method for removing onion weed.

Popular glyphosate weed killers include:

There are, however, some important things to keep in mind when using glyphosate-based products.

It is not a selective herbicide so will kill any other plants it comes into contact with, including your lawn. You’ll therefore need to carefully spot-treat the weeds.

You can do this either with a spray bottle with a directional nozzle or a special weed-killer applicator like the Yates Zero Weeding Brush (view at Amazon).

Also, keep in mind that The World Health Organization believes glyphosate to be a probable human carcinogen.

If you choose to use glyphosate, ensure you follow all recommended safety measures including doing it on a windless, dry day and wearing protective gear.

Other effective herbicides may include:

  • Imazaquin
  • 2,4-D, dicamba, mecoprop (MCPP)

How to get rid of onion weed naturally

Allium triquetrum 1 | Weed control
Allium triquetrum I Photo by Ewen Cameron (cropped) I Auckland Museum, Wikimedia I CC BY 4.0

Dig the onion weed out

The most effective natural method for getting rid of onion weed is to dig it out from the ground.

Use a garden spade, weed knife, or trowel and loosen the soil around each plant, then grab hold of its leaves and pull firmly. The plant should come out easily along with its roots, which are shallow and fibrous.

A pair of gardening gloves can protect your hands from irritation caused by the juice from the bulb.

Discard the plants in a bag or burn them, as this will prevent them from spreading further.

It’s important that you remove every bit of root, because if even small pieces are left in the ground they’ll grow into new plants.

Create a barrier that deprives onion weed of light

Because plants need sunlight to survive, they will eventually die if you cut off their light source.

For this method, lay down sheets of black plastic that are large enough to completely cover the area infested with onion weeds.

Peg the plastic in place and leave it in place for a month or more.

Keep in mind that this method will not only kill off the weeds but also dry out your soil and kill any other plants that are under the sheet, including your lawn.

Therefore, this is a fairly extreme method suited only for those with a large onion weed infestation.

Killing onion weed with vinegar

To add some extra potency to the digging up method, try spraying white vinegar in the hole once you have dug up each onion weed before refilling the hole with soil.

However, while this may help ensure the onion weed won’t re-grow, the vinegar will also damage the soil and any other plants it comes into contact with.

How to prevent onion weed from growing

Asphodelus fistulosus 1 | Weed control
Asphodelus fistulosus I Photo by Harry Rose I Flickr I CC BY 2.0

A healthy lawn is the best defence against Onion Weed.

If your soil lacks nutrients or if your grass is stressed for another reason, weed seeds will be more likely to germinate and take hold.

Ensure your lawn gets enough water and sunlight and is fed with a balanced lawn fertiliser.

Onion weed vs nutgrass

Cyperus rotundus | Weed control
Cyperus rotundus (nutgrass) I Photo by KevinTony I Wikimedia (cropped) I CC BY-SA 4.0

Before you can get rid of onion weed, it’s important to make sure that what you have is actually onion weed.

Onion weed has a resemblance to nutgrass, and the two types of weed often grow side by side. However, they’re not the same thing.

Nut grass spreads through the soil and creates hundreds of tiny round brown nuts, all of which will grow into new plants (that’s why it’s so hard to destroy nut grass).

Onion weed readily reproduces by seeds that travel on wind and water.

If you pull an onion weed plant out of the ground and see many small bulbs attached at the base that looks like cloves of garlic, then you are likely dealing with onion weed (these are where new plants will eventually sprout).

Onion weed FAQ

How to get rid of onion weed in buffalo grass?

To get rid of onion weed in buffalo grass your options are a glyphosate weed killer, digging them up manually, or creating a barrier that deprives them of sunlight (which will also kill your grass).

Does boiling water kill onion weed?

Boiling water will not kill onion weed. While hot water can be effective against weeds in general, it works best on broad-leafed weeds, as opposed to established perennials like onion weed.

Does roundup kill onion weed?

Glyphosate is the active ingredient in roundup, and it is the ingredient that kills onion weed. Roundup is a non-selective herbicide, which means that it will kill everything that it touches – including your lawn. If you are going to use roundup for getting rid of onion weed, be aware that Roundup can also be toxic for dogs, so keep them away while you are spraying.

Is onion weed toxic to dogs?

The smell is the only thing onion weed has in common with the vegetable of the same name. Onion weed is not a member of the onion family, so it is not harmful to dogs who ingest it.

Photo of author

Steve Kropp

Based in Melbourne, Steve's passion is vegetable gardening, and he’s been writing about it for almost 5 years. He also loves all things DIY and is always looking for a new project. When not working on his own garden projects or blogging, Steve enjoys spending time with his family, cooking meals with produce harvested from his garden, and coaching his son’s footy team.

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3 thoughts on “Australian Guide to Getting Rid of Onion Weed”

  1. I joined an organic community garden and was allocated a garden bed heavily populated by onion weeds. I did not know what they were so dug them out without digging very deep, which meant all the bulbs were left in the ground. Result was hundreds of new onion weeds popped up soon after. It is very difficult to eradicate them by hand as the bulbs can be deep down and the delicate connecting stem breaks very easily so the hard to find bulb remains in place at depth in the soil.

    Reply
  2. Hi Steve
    12/11/23
    help with onion weed
    If 1 seed sprouts and green stalk is pulled and that bulb remains in ground can it regrow?
    sincerely
    pat

    Reply
    • Yes, of the bulbs are left in the ground, they’ll continually resprout. You need to dig them out completely to get rid of the weed. Or, use a herbicide to kill them.

      Reply

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