Selfheal (Prunella vulgaris)
Selfheal is a creeping perennial weed that often appears in moist, shaded lawns throughout New Zealand. While some view it as a medicinal herb, most homeowners recognise it as a stubborn invader that forms thick mats through lawns and garden edges.
It spreads via creeping stems that root at the nodes, helping it quickly colonise damp or compacted soil. Its resilience and tolerance to many selective herbicides make it a particularly persistent turf weed.
Although it can reach up to 30 cm tall when left unmown, in lawns it stays low to the ground, forming dense patches that crowd out desirable grasses.
Identification
Selfheal forms sprawling mats of dark green leaves that grow in opposite pairs along creeping stems. The stems root freely as they spread, creating thick patches across the lawn surface.
The leaves are oval and slightly larger than those of pennyroyal, a similar mat-forming species from the same plant family (Lamiaceae). Crushing selfheal leaves doesn’t release the strong minty smell that pennyroyal gives off.
In spring and early summer, selfheal produces distinctive upright flower spikes topped with clusters of purple-blue flowers arranged in layers. After flowering, the seed heads turn brown but remain attached to the stems for some time.
Why It’s a Problem
Selfheal thrives in damp, shaded, and compacted areas where grass struggles to compete. It’s especially common in poorly drained lawns or beneath trees and hedges.
Its creeping growth habit allows it to choke out turfgrasses, and mowing alone won’t stop it — in fact, the plant adapts easily to close cutting. Because it tolerates many standard lawn herbicides, it often survives where other weeds are easily removed.
Management and Prevention
The best long-term approach to managing selfheal is improving lawn health and removing the conditions that allow it to spread.
Cultural control methods:
- Improve drainage: Aerate regularly to relieve compaction and encourage root growth in grasses.
- Increase sunlight and air movement: Thin nearby trees or shrubs to reduce shade and moisture retention.
- Fertilise and overseed: Strong, actively growing grass will outcompete selfheal. Use quality grass seed to thicken bare patches.
- Mow regularly: Keep mowing heights moderate to favour grass while discouraging low-creeping weeds.
Manual control:
For small infestations, selfheal can be hand-pulled or dug out. Be sure to remove the creeping runners, as any piece left behind can regrow.
Chemical Control:
Selfheal is tolerant of many selective herbicides including MCPA, 2,4-D, clopyralid, and triclopyr when used alone.
Effective options include:
Triclopyr/picloram mixtures (NZLA Gold): Provide good suppression, though regrowth can still occur and follow-up treatments may be needed.
To ensure lasting control, combine chemical treatment with soil improvement and overseeding once weeds die back.