Pearlwort (Sagina procumbens)
Pearlwort is a low-growing, mat-forming perennial weed that often resembles moss. It thrives in damp, shaded, or compacted soils and is common in lawns, garden edges, paths, and between paving stones. It’s most active through the cooler months and can persist year-round where moisture is consistent.
Because it hugs the ground and roots at multiple points along its stems, pearlwort easily evades mowing and can spread quickly across open patches of turf. Once established, it can form thick mats that smother desirable lawn grasses.
Identification
Pearlwort forms dense, creeping mats with fine, smooth stems that root at the nodes. The small, narrow leaves grow in opposite pairs and often appear in clusters along the stems. The leaves are bright green, hairless, and slightly fleshy.
Tiny white flowers appear through spring and summer, each with four small petals. The flowers are often followed by small seed capsules that contain hundreds of fine, dust-like seeds capable of remaining viable in the soil for years.
Why It’s a Problem
Pearlwort competes with lawn grasses for moisture and space, especially in shaded or compacted areas. Its low, sprawling habit makes it difficult to mow effectively, and it quickly spreads in weak turf. It’s also resistant to many commonly used lawn herbicides, which makes it difficult to remove once established.
Management and Prevention
Cultural control methods:
- Improve drainage: Pearlwort thrives in damp, compacted soil. Aerate regularly and topdress with sand to improve water movement.
- Encourage dense turf growth: Maintain good fertiliser and mowing practices to create a thick lawn canopy that blocks light from reaching the soil.
- Reduce watering frequency: Allow the surface to dry between irrigation cycles where possible.
- Hand removal: Small patches can be lifted with a knife or trowel, but ensure the entire mat and roots are removed to prevent regrowth.
Chemical Control
Pearlwort is tolerant of many selective herbicides, so chemical control should be used in combination with cultural improvements.
Effective options include:
- 2,4-D-based herbicides (Cleansweep or Soft Touch) which provide the best selective control in turf when applied during active growth.
- Triclopyr/picloram mixtures (NZLA Gold) may help suppress established infestations.
- Glyphosate can be used for spot-spraying in non-turf areas, though it will kill any grass it contacts.
Repeat treatments are often required, as new seedlings will emerge from the seed bank after rain or soil disturbance.