G’day, Nikolai here from The Lawn Firm. If you’ve noticed fine, hollow leaves that smell like onion when crushed, you’re dealing with onion weed. It spreads fast via bulbs and tiny bulblets. I see it across Canberra lawns every season, especially in thinner turf. Here’s my clear plan to stop it.

What onion weed looks like

Leaves: Fine, round, hollow leaves that rise upright from the base
Smell: Distinct onion/garlic smell when crushed
Growth: Clumps that multiply, with many small bulblets around a main bulb
Flowers: Delicate white flowers on slender stalks (seasonal)

Why onion weed takes hold in Canberra

Bulb spread: Each plant carries multiple bulblets - disturbing the soil spreads them
Thin turf: Gaps allow clumps to establish and expand
Compacted clay: Weak turf can’t compete
Dry patch: Hydrophobic soil creates bare spots onion weed exploits

When onion weed is most active

You’ll notice new shoots from late winter into spring, with growth continuing through summer. I focus on early action before heavy flowering and bulblet drop.

How I confirm onion weed on site

Crush test: Lightly crush a leaf; onion/garlic smell = positive
Leaf shape: Round and hollow, unlike flat grass blades
Clump check: Gently loosen soil; multiple bulblets surround the base

Prevention that works

Thicken the lawn: Overseed and top dress 5–8 mm in autumn or spring to close gaps
Core aeration: Open compacted clay in spring or autumn so turf wins space back
Seasonal feeding: Keep density up so bulbs struggle to re-sprout
Wetting agents in warm months: Improve water movement and reduce dry patch gaps
Mowing discipline: Maintain height; avoid scalping that creates openings

Control once onion weed appears

Hand removal (small clumps): Water or wait until after rain, then use a narrow trowel to lift the entire bulb cluster. Go deep and slow. Do not tear as leftover bulblets regrow. Bag and bin everything.
Targeted control (wider spread): Use a selective approach suitable for onion-type weeds. Correct timing and repeat passes are often needed because of bulblets. Avoid blanket treatments on stressed turf.
Timing tip: Act before flowering and repeat after new shoots appear from remaining bulblets.

Aftercare to stop it returning

Backfill and level: Replace soil and press lightly to prevent hollows
Top dress lightly: 5–8 mm sandy loam to even scars
Overseed thin areas: Restore coverage to block light reaching new bulblets
Light fertilise: Support steady grass growth
Deep watering, less often: Drive roots down and keep the canopy dense

Common mistakes I fix

Pulling by hand without a tool: Bulbs snap, leaving bulblets behind
Aggressive cultivation: Breaks clumps and spreads bulblets
Scalping the area: Weakens turf and speeds reinfestation
One-and-done approach: Onion weed often needs repeat passes as new bulblets emerge

My Canberra timing guide

Late winter / early spring: Identify, start removal, raise mowing height, feed
Spring: Core aerate compacted areas, overseed, top dress, repeat checks
Summer: Maintain deep watering, use wetting agents, keep the canopy closed
Autumn: Strengthen roots, close gaps, and schedule follow-up passes if needed

DIY or call The Lawn Firm?

You can lift a few clumps yourself if you work carefully. For bigger outbreaks, timing and technique decide the result. I identify the spread pattern, apply targeted control, and line up aeration, overseeding, top dressing, wetting agents, and seasonal feeding so onion weed loses its foothold, and your grass wins for good.