Sheep’s Sorrel (Rumex acetosella)
Sheep’s sorrel is a low-growing perennial weed that thrives in dry, acidic soils and poorly nourished turf. Common throughout New Zealand, it spreads by a creeping root system that can form large reddish patches in lawns and pastures, especially in spring.
It prefers conditions where desirable grasses struggle to grow, such as compacted or sandy soils with low pH. Although not highly competitive, it’s persistent once established and can quickly reappear after mowing or light herbicide use.
Identification
Sheep’s sorrel forms small rosettes of distinctive arrow-shaped leaves, each with backward-pointing lobes near the base. These rosettes are connected underground by slender, reddish-brown creeping roots that allow the weed to spread laterally and form colonies.
In spring, reddish flower stems rise from each rosette, producing small clusters of rust-red seed heads that can tint entire patches of turf with a reddish hue. The seed heads resemble miniature dock seed spikes, which makes sense given that sheep’s sorrel and dock belong to the same plant family (Polygonaceae).
Why It’s a Problem
Sheep’s sorrel competes with turfgrasses by spreading through its creeping roots and surviving mowing, drought, and acidic soil where most grasses struggle. It often appears in lawns that are compacted, nutrient-poor, or low in lime, signalling soil imbalance.
While not particularly aggressive in fertile, healthy turf, its ability to thrive under stress conditions means it can persist and spread unless the soil environment is corrected.
Management and Prevention
The key to managing sheep’s sorrel is improving soil conditions and encouraging vigorous turf growth.
Cultural control methods:
- Correct soil pH: Apply lime to raise pH levels. Sheep’s sorrel thrives in acidic soil, so neutralising acidity reduces its advantage.
- Improve soil fertility: Regular fertilisation promotes dense turf cover that shades out new sorrel growth.
- Aerate and topdress: Break up compacted soil and improve structure to enhance drainage and grass root development.
- Overseed thin areas: Maintain thick, healthy grass cover to reduce light reaching the soil surface.
- Irrigate sensibly: Avoid over-drying sandy soils where this weed often flourishes.
Manual control:
Small patches can be hand-pulled or dug out, though care must be taken to remove all root fragments, as any remaining pieces can regrow.
Chemical Control:
Sheep’s sorrel is resistant to many common selective herbicides, making chemical control more challenging.
Effective herbicides include:
- Triclopyr/picloram mixtures (NZLA Gold) is strong control in lawns and turf.
- 2,4-D/dicamba combinations – suitable for home lawns and general turf maintenance.
- Glyphosate – can be used for spot-spraying or renovation, though adding tribenuron or dicamba improves effectiveness.
Because this species spreads via creeping roots, translocated herbicides are more effective than contact types. A follow-up application may be required to eliminate regrowth from remaining root fragments.
Maintaining good lawn nutrition, neutral soil pH, and healthy turf density will help prevent re-establishment.