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Weed guide
Black medic
Medicago lupulina · Pea family (Fabaceae)
Also called black medick (UK, New Zealand and Canada), yellow trefoil (New Zealand).
Illustration
A small clover look-alike with tiny yellow pom-pom flowers that turn into coiled black seed pods. It moves into thin, dry, under-fed lawns, so a healthier lawn is the long-term fix.
How to spot it
- Three leaflets, with the middle one on its own short stalk (clover's leaflets all join at one point).
- Each leaflet ends in a tiny point and is toothed towards the tip; 4–25 mm long and slightly hairy.
- Small, dense, round yellow flower heads, 6–12 mm across.
- Clusters of tiny coiled, kidney-shaped pods that turn black, each holding one seed.
- Downy stems that sprawl out from a single taproot but don't root along the ground.
Easily confused with
Lesser trefoil (yellow suckling clover)
Its dead flowers stay on as brown papery heads that hide the pods; black medic's coiled black pods are on show.
White clover
White flowers, leaflets that all join at one point, and creeping stems that root.
Creeping oxalis
Heart-shaped leaflets and yellow flowers with five separate petals.
Where it's a problem
- UK and Europe: Native, and a common lawn weed.
- Australia: Naturalised in NSW, Victoria, Tasmania, South Australia and Western Australia.
- New Zealand: Introduced; flowers from about November to May.
- North America: Seen as a minor nuisance rather than a serious threat, and a sign of thin, under-fed turf.
What to do
- Pull plants while they're young and the soil is moist, before the pods turn black.
- Mow off the flower heads before they set seed.
- Raise the mowing height to at least 7.5 cm, and feed, water and aerate the lawn so the grass thickens up.
- In garden beds, a mulch at least 7.5 cm deep stops the seedlings.
If you use a herbicide, choose one labelled for black medic and follow the label and local rules. Medics shrug off many lawn weedkillers, so improving the lawn usually works better. If you do use one, spot-treat rather than spraying the whole lawn.
Follow your local council's guidance for disposing of weeds. Councils usually advise against putting weeds like this in the green waste / vegetation bin or the compost.
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Sources
- University of California IPM: Black medic
- Penn State Extension: Black medic
- Utah State University Extension: Black medic
- Purdue University Turf Science: Black medic
- PlantNET, Royal Botanic Garden Sydney
- Flora of New Zealand: Medicago lupulina
- Michigan State University MISIN: Black medic
Facts checked Sunday 27 September 2026. General guidance only: follow your local council, agency and product label.