Groundsel (Senecio vulgaris)
Groundsel is a small, upright annual weed that thrives in disturbed soil and garden edges, and it can occasionally appear in thin or patchy lawns. It germinates and flowers at almost any time of year, but is most common from spring through autumn when temperatures are warm and soil moisture is high.
Although short-lived, groundsel can complete its life cycle in as little as five to six weeks, producing thousands of tiny wind-blown seeds. This quick turnover allows it to reappear soon after mowing, weeding, or garden clean-ups. It’s often one of the first weeds to colonise freshly turned soil, bare patches in turf, and even the surface of mulches in flower beds.
Identification
Groundsel grows 10–40 cm tall with soft, fleshy stems and lobed green leaves that sometimes look slightly shiny. The stems branch freely, forming clusters of small cylindrical flower heads rather than showy petals.
Each flower head is green with a yellow centre, around 5 mm wide, and remains mostly closed until the seed matures. Once ripe, the heads release hundreds of fine white seeds, each with a small “fluffy” pappus that helps them blow long distances on the wind.
It’s sometimes mistaken for gravel groundsel, which grows more prostrate and has open, yellow daisy-like flowers rather than the tight, tubular heads of true groundsel.
Why It’s a Problem in Lawns
Groundsel isn’t aggressive in thick, healthy turf, but it can quickly invade thin or patchy areas where grass coverage is poor. Its rapid life cycle means it can produce several generations over one season, creating a persistent seed bank that keeps reappearing after each mowing or renovation.
It also germinates easily on top of mulches and compost, so nearby garden beds can act as a constant source of new seed drifting into the lawn.
Control in Home Lawns
Groundsel is one of the easier weeds to control if caught early. Because it grows from seed and has shallow roots, both manual and chemical methods are effective.
Best control methods:
- Physical removal: Hand-pull or hoe out young plants before flowering. Even uprooted plants can mature seed as they wilt, so remove them completely from the lawn or garden.
- Chemical control: Use selective turf herbicides containing MCPA, dicamba, or triclopyr/picloram (NZLA Gold) for effective control. These actives target small broadleaf weeds like groundsel without damaging most turf species.
- Cultural management: Maintain a dense, well-fed lawn to reduce bare soil. Reseed thin areas promptly to prevent new germination.
- Mulch management: In garden beds, apply a thick layer (at least 5 cm) of quality mulch to block sunlight and stop seeds germinating in the soil.
Prevention Tips
- Mow regularly to prevent flowering.
- Remove the first flush of seedlings after soil disturbance or renovation.
- Keep mulched areas tidy, removing any plants that sprout on top before they seed.
- Avoid bringing in contaminated compost or soil that may contain groundsel seed.