Subterranean Clover (Trifolium subterraneum)
Subterranean clover is a low-growing annual clover that often appears in New Zealand lawns over autumn and winter. It germinates as soils cool in early autumn, grows through winter, flowers in spring, and then dies off as summer heat dries the soil.
While it’s valued in pastures for its nitrogen-fixing ability and feed value, it’s considered a nuisance in lawns. Subterranean clover forms flat mats of foliage that break up the smooth, uniform appearance of turf. It thrives in areas where lawns are thin, compacted, or under-fertilised, especially those that dry out over summer or are cut too short.
Because it can fix its own nitrogen, it often takes advantage of nutrient-poor conditions, becoming more dominant in lawns that receive infrequent fertiliser.
Identification
Like all clovers, subterranean clover has trifoliate leaves (three leaflets per leaf). Its leaves are noticeably hairy, unlike those of suckling or white clover, and may show faint white markings. The leaflets are larger than suckling clover but typically smaller and duller than white clover.
The plant sits very flat to the ground, forming spreading mats with stems that root along the soil surface. These stems help it persist through mowing and mild treading. The flowers are white to pale pink, small, and tucked down close to the base of the plant rather than standing upright. After flowering, the seed heads are drawn into the soil—hence the name subterranean—allowing the seeds to survive dry summers and germinate again the following autumn.
Why It’s a Problem in Lawns
Subterranean clover competes with grass for light, water, and nutrients, particularly in lawns that are dry or nutrient-deficient. It can tolerate close mowing and drought better than most lawn grasses, so it often takes over during late spring when grass growth slows.
Once established, it can be difficult to remove without damaging surrounding grass, and because it reseeds so effectively, it tends to return each year unless conditions are corrected. Its presence is often a sign of low soil fertility, dry conditions, or scalped mowing.
Control in Home Lawns
Subterranean clover can be controlled successfully with herbicides, though maintaining good lawn health is equally important to prevent it from re-establishing.
Best control methods:
- Physical removal: Hand-pull small patches before flowering, ensuring the plant is lifted completely. Dispose of clippings to prevent reseeding.
- Chemical control: Apply a selective broadleaf herbicide containing clopyralid (NZLA BWC), dicamba, or triclopyr/picloram (NZLA Gold) for strong control. Avoid composting treated clippings, as residues can remain active for several months.
- Early intervention: Products containing ioxynil + bromoxynil + mecoprop (such as Image) may suppress seedlings if applied early in autumn before the plants mature.
- Cultural management: Fertilise with a nitrogen-rich lawn fertiliser in autumn and spring to give grass a competitive edge. Maintain an appropriate mowing height and water deeply but less often to encourage deeper root growth.
Prevention Tips
- Feed the lawn regularly with a balanced fertiliser containing nitrogen to discourage nitrogen-fixing weeds.
- Aerate compacted areas annually to promote healthy grass roots.
- Reseed thin or bare spots in autumn to maintain a dense lawn canopy.
- Avoid mowing too low; short mowing exposes soil and encourages clover germination.