Pasture Weed Watch

The creeping problem of penny royal

PENNY ROYAL ( Mentha pulegium) is native to Europe, North Africa and Asia and is commonly found throughout turf, lawns and pastures in New Zealand.

‘Mentha' is Latin for mint and ‘pulegium' is Latin for fleabane. Crush this weed with your fingers and it imparts a strong mint smell. This is associated with an age-old belief that it could suppress fleas.

Perennial penny royal is very hardy. It can establish under high rainfall conditions and seeds have been known to sprout following long periods of anaerobic soil conditions and floods.

As the seedling develops, it establishes long, low-growing stems (stolons) and roots at the nodes. This produces a mat-like structure in pasture and lawn, keeping it below the cutting line of your mower.

As the flowering stem is produced, the plant severs all interconnecting stolons. The flowering plant can stand up to 50cm high, showcasing a deep purple flower. It is quite pretty when in flower from November through until April.

How to control it

Penny royal can infest pasture, reducing production. It's best to try eradicating it in autumn or spring when it is actively growing.

The problem for organic gardeners and farmers is that penny royal is too low to be mown off for most of the year, and it's hard to spot until it flowers in summer. A herbicide such as 2,4D (Baton) applied in spring or autumn will help give control of penny royal in your pasture. Always read the label of the product you have purchased for spraying instructions. Use on actively growing plants to ensure successful control.