Appearance

White or Dutch clover (Trifolium repens) is comparatively large-leaved and has an open habit of growth. The flowers are white or pink.

Lesser yellow trefoil (Trifolium dubium), a member of the clover family, is a small-leaved, procumbent annual weed.  It forms a flattened, roughly circular mat of interlaced thin wiry stems, with tiny trifoliate leaves. Many small multiple heads of pale yellow flowers are produced throughout the summer months. 

Other related species include hare's foot (T. arvense) with its woolly haired leaves and flowers, slender trefoil (T. micranthum) bearing tiny yellow flowers, birds foot trefoil (Lotus corniculatus) with robust stems and bright orange-yellow flowers and black medick (Medicago lupulina) with yellow flowers and clusters of black seeds.

The problem

White or Dutch clover (Trifolium repens) may be encountered on all types of soil but is more commonly found on medium to heavy alkaline soils. Its roots form readily along the creeping, spreading stems.

Lesser yellow trefoil (Trifolium dubium) is usually most troublesome on lighter, sandy soils, particularly where the grass is weak through lack of regular feeding. It forms a deeply penetrating tap root, seeds freely and if scattered plants are ignored, large colonies quickly form. It survives close mowing – a practice which can further weaken turf on poor soils.

Lotus corniculatus (birds foot trefoil), Medicago lupulina (black medick), Trifolium arvense (hare's foot) and Trifolium micranthum (slender trefoil) spread mostly by seed.

Control

Plants that out-compete other more desirable plants or simply invade half the garden are classed as weeds and require control. First, consider whether this can be done using non-chemical means such as digging out or suppressing with a mulch. 

Where these methods are not feasible, chemical controls may need to be used. Choose a weedkiller that is most appropriate for that purpose by reading the label carefully before buying or using. 

Non-weedkiller control

Try non-chemical control options in the first instance;

• Where practical, carefully lift out isolated specimens using a hand fork
• If the weed is widespread, rake the turf to lift stems before mowing and always use a grass-box on the mower to minimise seed dispersal
• Apply lawn fertilisers regularly to strengthen the grass, both in summer and in autumn. Begin feeding in April when growth starts again with the arrival of settled, milder weather
• Apply a single application of a proprietary spring lawn fertiliser followed at six to eight-week intervals by an application of sulphate of ammonia at 15g per sq m (½oz per sq yd); its nitrogen content encourages grass growth and acts as a deterrent to the clover
• Even distribution of  sulphate of ammonia is essential, or it may scorch or burn the grass. To minimise scorch risk, bulk it out with three or four times its weight of dry sterilised soil or sharp sand. Apply only when the soil is moist and preferably in showery weather. Alternatively, apply lawn fertiliser at 30g per sq m (1oz per sq yd) in April and repeat the dressing at about six-week intervals
• Do not apply spring or summer fertilisers or sulphate of ammonia after early August. If the grass is still in poor condition in late summer and the lawn has been neglected in the past, apply a proprietary autumn lawn fertiliser in September. If, however, the grass has been regularly fed, defer further feeding until the following spring, as the use of an autumn fertiliser with its higher level of phosphorus may do the clover more good than the grass

Weedkiller control

Lawn weedkillers

White or Dutch clover (Trifolium repens) is relatively susceptible to dicamba, and mecoprop-P (e.g Doff Lawn Weedkiller, Crowne Green Lawn Weedkiller, Westland Resolva Lawn Weedkiller Extra or SBM Job Done Lawn Weedkiller and may be eliminated after one or two applications. Lesser yellow trefoil (Trifolium dubium), however, shows strong resistance to the majority of lawn herbicides. Products containing fluroxypyr (Weedol Lawn Weedkiller, Weedol Lawn Weedkiller Ready to Use or Roundup Lawn Weedkiller) are particularly effective at controlling clovers, including the more persistent species such as Trifolium dubium. 

The other clover-like species occasionally encountered as lawn weeds, including Lotus corniculatus (birds foot trefoil), Medicago lupulina (black medick), Trifolium arvense (hare's foot) and Trifolium micranthum (slender trefoil) are similar to Trifolium dubium in their resistance to lawn weedkillers and the same control measures apply. One weedkiller (Weedol Lawn Weedkiller, Weedol Lawn Weedkiller Ready to Use or Roundup Lawn Weedkiller), containing fluroxypyr, MCPA and clopyralid, is also listed as controlling Medicago lupulina.

Applications after August are increasingly less effective and as the majority of clovers found in lawns self-seed freely, further applications the following spring will inevitably be required.

Treated clippings

Do not add the first lawn clippings after application of a lawn weedkiller to the compost heap. To avoid possible contamination of compost, do not collect the clippings at all but mow frequently and allow the short clippings to remain on the surface of the lawn. These will quickly disperse to leave an acceptable finish.

New lawns

Weedkillers often cause severe damage if applied to lawns within six months of sowing or turf-laying. However, materials containing fluroxypyr as one of their ingredients are claimed to be safe to use after only two months.

Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 1b and c)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers