Onion weed: why it keeps coming back, and how to beat it

If onion weed keeps coming back no matter how many times you pull it, that's not bad luck — it's how the plant is built. Every clump grows from a bulb studded with small bulblets, and tugging on the leaves snaps those bulblets loose in the soil rather than removing them, so a single pull can leave behind more plants than it started with. The fix is to dig out the whole clump and its bulblets, starve the bulb with repeated cutting, or spot-spray it carefully — never hand-pull a lawn full of it and expect that to be the end of it.

What most Victorian gardeners call onion weed is usually Nothoscordum, a perennial bulb plant with thin, flat, strappy leaves that give off a strong onion smell when crushed, and small white star-shaped flowers held on a bare stalk in spring. It dies back over summer, resprouts from autumn onward, and sets seed in summer that spreads on the wind — which is why it can turn up in a new corner of the garden even after you've cleared the original patch.

Onion weed, onion grass or three-cornered garlic?

Before you treat anything, it's worth checking which weed you've actually got, because three different lawn and garden weeds get called "onion weed" in everyday conversation and they don't all respond to the same treatment.

Plant	Grows from	Stem & leaves	Flowers	Smell
Onion weed (Nothoscordum)	True bulb with bulblets	Round stem, flat strappy leaves	White, star-shaped, upright, spring	Strong onion when crushed
Onion grass (Romulea rosea)	Corm	Wiry, grass-like leaves	Pink to mauve, low, spring	Little to none
Three-cornered garlic (Allium triquetrum)	True bulb	Triangular stem (feel it between your fingers)	White, drooping, bell-shaped	Strong garlic

Onion grass is a completely different plant — it's the one most likely to be in your actual lawn among fine grass leaves, and despite the name it barely smells of onion at all. Three-cornered garlic is a declared restricted weed in Victoria, meaning it can't knowingly be sold, traded or planted, and it tends to favour garden beds and shaded fence lines more than open lawn. True onion weed sits in between: not currently on Victoria's declared weeds list, but every bit as persistent as its relatives once it's established. The removal principles below work for all three, since all three spread from underground storage organs that punish pulling.

Why onion weed is so hard to kill

Three things work against you. First, the leaves have a thin, waxy coating that sheds spray rather than absorbing it, so herbicide often beads up and runs off instead of being taken up by the plant. Second, the bulb doesn't sprout all its bulblets at once — it releases them gradually over more than one season, so a patch that looks gone can still have bulblets waiting underground to come up the following autumn. Third, the plant disappears completely over summer dormancy, which means there's nothing to treat for months and it's easy to forget about until it reappears.

How to get rid of onion weed for good

Dig out the whole clump

For a handful of patches, this is the most reliable non-chemical option. Loosen the soil around the base of the clump with a trowel or hand fork and lift the whole thing — bulb, bulblets and surrounding soil — rather than gripping the leaves and pulling straight up. Bag the lot and put it in the general waste bin; don't add it to a home compost, since compost heaps rarely get hot enough to kill the bulblets and you'll just be spreading the problem with your next load of compost.

Starve the bulb with repeated cutting

Where onion weed is scattered through a lawn rather than in isolated clumps, mowing or whipper-snippering the leaves back to ground level every time they appear will gradually exhaust the bulb's stored energy, since the plant can't photosynthesise without leaves. It's slow — expect to keep at it through a full growing season or two — but it needs no chemicals and works alongside your normal mowing routine.

Spot-spray with a weed wand or paintbrush

For lawn infestations too big to dig out, a non-selective glyphosate herbicide applied carefully to the leaves of the onion weed only, using a weed wand, sponge applicator or even a paintbrush dipped in the mixed solution, kills the plant without taking out the surrounding grass. Adding a few drops of a wetting agent or a small amount of dishwashing detergent to the mix helps it stick to those waxy leaves instead of beading off. Spray while the plant is actively growing, before it flowers, and expect to repeat the treatment on new growth over the following seasons — one pass rarely gets every bulblet. Broadcast-spraying glyphosate over the whole lawn isn't an option, since it will kill the grass along with the weed.

Professional and selective options

Some selective herbicides used commercially on onion weed and its relatives, such as those containing iodosulfuron-methyl-sodium, are restricted to licensed pest control operators rather than sold for home use. If a lawn has heavy, spreading infestation across most of the yard rather than a few patches, this is the point where getting a professional in for targeted treatment is usually faster and more reliable than DIY spot-spraying square metre by square metre. It's the kind of job we handle as part of a routine weeding visit alongside your regular mow.

Is onion weed dangerous to pets or people?

Treat it as a risk rather than a serious hazard. Onion weed's bulbs contain sulfur compounds similar to those in true onions and garlic, which are well documented to cause gastrointestinal upset and, in enough quantity, damage to red blood cells in dogs and cats. A dog digging up and chewing on a single bulb occasionally is unlikely to eat enough to cause serious harm, but if you notice vomiting, lethargy, pale gums or dark urine after your pet has been rooting around in a patch of it, contact your vet or the Animal Poisons Centre on 1300 869 738. There's no reliable evidence it's a significant hazard to people beyond mild skin irritation from the sap in sensitive individuals, but wearing gloves while digging it out is sensible regardless.

Stopping it coming back

Onion weed, like most bulb weeds, establishes fastest in thin or bare turf where there's little competition, so the same lawn-health basics that keep other weeds down help here too. A few things make a real difference over a season or two:

• Mow at the correct height for your grass type instead of scalping it — a denser canopy shades out germinating weed seedlings and gives onion weed less bare ground to colonise. See our mowing height guide for exact settings by grass type.
• Keep up a regular mowing schedule through the growing season so any new onion weed leaves get cut back before they can properly refuel the bulb underground — see how often to mow by season and grass type.
• Fix bare and compacted patches with topdressing, light aeration and overseeding or runners, since bare soil is exactly where onion weed and onion grass get their foothold.
• Follow a proper autumn and spring feeding schedule — a dense, actively growing lawn out-competes emerging weeds far better than a stressed one. Our Victorian lawn care calendar sets out the full month-by-month timing.

None of this replaces digging, cutting or spot-spraying an existing infestation, but a thicker, healthier lawn means fewer bare patches for the next season's bulblets to establish in, and most yards see noticeably less onion weed each year once mowing and feeding are on track.

Frequently asked questions

What's the difference between onion weed and onion grass?

They're different plants that get lumped under the same nickname. Onion weed (Nothoscordum) is a true bulb with flat, strappy leaves and a strong onion smell when crushed, flowering white in spring. Onion grass (Romulea rosea) grows from a corm, has wiry grass-like leaves, small pink to mauve flowers, and doesn't smell like onion at all. Both are common in Victorian lawns and both are fiddly to control, but it's worth checking which one you actually have before you spray.

Is onion weed the same as three-cornered garlic?

No, though the names get used interchangeably. Three-cornered garlic (Allium triquetrum) has a distinctly triangular stem, drooping bell-shaped flowers, and a stronger garlic smell, and it's a declared restricted weed in Victoria. Onion weed (Nothoscordum) has a round stem and star-shaped upright flowers, and doesn't carry the same formal declared status here.

Can you just pull onion weed out by hand?

Pulling is the one thing that reliably makes it worse. The bulb carries small bulblets loosely attached to it, and the tug of pulling snaps them off in the soil, where each one can grow into a new plant. Dig around the whole clump with a trowel instead of gripping the leaves and pulling straight up.

Is onion weed toxic to dogs or cats?

Treat it as a risk. Its bulbs contain sulfur compounds similar to true onions, which can cause gastrointestinal upset and, in quantity, red blood cell damage in dogs and cats. Contact your vet or the Animal Poisons Centre on 1300 869 738 if your pet shows vomiting, lethargy, pale gums or dark urine after being in a patch of it.

When's the best time to treat onion weed in Victoria?

Late winter into early spring, while the leaves are up and the plant is actively growing but hasn't flowered and seeded yet. Once the leaves die back over summer there's nothing left above ground to treat, so digging or spraying has to happen while you can actually see the plant.