Scarlet Pimpernel (Anagallis arvensis)
Scarlet pimpernel is a small, low-growing annual weed that creeps across bare or open areas in lawns and gardens. It can germinate year-round in most parts of New Zealand, especially in moist, sunny conditions.
Although it’s not highly competitive, it spreads easily and can form dense mats in lawns where grass coverage is thin. It’s also common in flowerbeds, vegetable gardens, and disturbed soil, where it weaves through other plants.
The species has been nicknamed poor man’s barometer or shepherd’s weather glass because its flowers close in cloudy or humid weather — an old-fashioned sign of rain on the way.
Identification
Scarlet pimpernel has smooth, square stems that sprawl outward, often branching at right angles. The leaves grow in opposite pairs and are hairless, oval-shaped, and stalkless. Tiny black dots (glands) are often visible on the undersides of the leaves.
Its flowers are small, with five rounded petals that are typically orange-red, though some varieties can appear pink or blue. They open only in bright sunlight and close when the weather turns dull or humid. After flowering, round seed capsules form, each containing numerous fine seeds that allow it to spread quickly.
It’s often confused with chickweed, which has white flowers, round stems, and a single line of hairs along the stem. Staggerweed and red dead-nettle also look similar but can be distinguished by their hairy stems and differing flower colours.
Why It’s a Problem
In lawns, scarlet pimpernel grows flat against the ground, allowing it to avoid mower blades. It can quickly fill bare patches, reducing turf quality and creating uneven colour and texture.
Because it produces many seeds that survive in the soil, it can reappear every year if not controlled early. In flowerbeds, its scrambling habit allows it to tangle through ornamental plants and seedlings, competing for space and light.
Management and Prevention
Scarlet pimpernel is relatively easy to control through good lawn maintenance and early intervention.
Cultural control methods:
- Maintain dense turf cover: Overseed thin or bare patches to prevent seed germination.
- Improve drainage and fertility: Weeds like pimpernel thrive where lawns are weak. Fertilise and aerate compacted soils to strengthen grass growth.
- Hand weeding: The weed is shallow-rooted and easy to pull, especially after rain. Remove before flowering to prevent seeding.
- Mulching: In garden beds, a good mulch layer prevents seeds from germinating.
Chemical Control:
Scarlet pimpernel is susceptible to most turf herbicides, but some products give better results than others.
Effective options include:
- Mecoprop/ioxynil/bromoxynil mixtures (Image): Works well on young plants in lawns.
- Triclopyr/picloram mixtures (NZLA Gold): Provide strong control in established turf.
- Dicamba/2,4-D mixtures (Banvine, Bandit): Suitable for general lawn and garden turf use.
Avoid relying on clopyralid (NZLA BWC), as scarlet pimpernel shows tolerance to this herbicide. Apply treatments while the weed is actively growing, and follow up with overseeding once the weed dies off to restore turf density.