Hedge Mustard (Sisymbrium officinale)
Hedge mustard is a common annual weed found throughout New Zealand, often popping up in lawns, garden beds, roadside verges and waste areas. It germinates in spring or autumn, quickly forming a flat rosette before sending up tall, wiry flowering stems that can reach up to a metre high.
Although more common in disturbed soil and neglected areas, it can also establish along the edges of thin or compacted lawns. Once it flowers, it spreads thousands of seeds that can lie dormant in the soil for years, making it a persistent nuisance if left unchecked.
Historically, hedge mustard has even been used as a herb in Europe and for traditional remedies — but in lawns, it’s simply an unwanted intruder that thrives where the grass cover is poor.
Identification
In its early stage, hedge mustard forms a rosette of lobed green leaves that sit close to the ground, similar to sow thistle or Cape weed. As it matures, it produces multiple upright, branching stems covered in small yellow flowers clustered at the top.
Each flower measures only a few millimetres across and is followed by slender seed pods that run parallel to the stem, unlike wild turnip or wild radish whose pods stick out.
The stems are coarse and slightly hairy, giving the plant a wiry appearance — which may explain why some people mistakenly call it “wireweed” (a completely different species).
Why It’s a Problem in Lawns
Hedge mustard competes with grass for space and nutrients, especially in thin, open, or compacted lawns. Because it grows upright and fast, it quickly becomes noticeable above the mown surface. It can also spread from neighbouring gardens or roadside areas via wind-blown seed.
Its deep taproot helps it survive in poor, dry soil, and regular mowing alone often isn’t enough to stop it from re-emerging once established.
Control in Home Lawns
Hedge mustard is generally easy to control in lawns when caught early, especially before flowering.
Best control methods:
- Physical removal: Hand-pull or dig out plants before they flower. The rosette stage is easiest to remove.
- Chemical control: Use selective turf herbicides containing MCPA, dicamba, or picloram/triclopyr (NZLA Gold). These products will kill hedge mustard without damaging most lawn grasses.
- Timing: Treat in late autumn or early spring when plants are small and actively growing. Once flowering stems appear, the plant becomes tougher and harder to kill.
- Cultural control: Maintain a dense lawn through fertilising, aeration and regular mowing. A strong turf canopy will outcompete new seedlings and prevent re-infestation.
Prevention Tips
- Reseed bare or open patches where hedge mustard may germinate.
- Avoid over-watering or compacting the soil.
- Keep mowing heights moderate to shade out young weeds.
- Clean mower decks if cutting areas with heavy infestation to avoid spreading seed.