Twin Cress (Lepidium didymum)
Twin cress is a low-growing annual weed that often appears in bare or recently disturbed soil, especially in lawns, gardens, and young pastures. It can germinate almost any time of year, though it’s most common in spring and autumn when conditions are mild.
In lawns, it forms flat, spreading mats that hug the ground, competing with grass and leaving patchy, uneven areas. In pastures, it’s more than just a visual nuisance — if eaten by lactating cows, it can taint milk, causing processors to reject the supply until the issue is resolved. That’s why dairy farmers keep a close eye on it.
Although it’s sometimes mistaken for land cress, twin cress is a very different species — smaller, faster growing, and much more aggressive in bare soil.
Identification
Twin cress starts life as a flat rosette with leaves radiating from a central growing point. The leaves are made up of small lobed leaflets, which are irregular — there are usually more lobes on one side than the other, giving the leaf a lopsided look.
As the plant matures, it sends out sprawling stems that creep across the soil surface, forming mats similar in shape to wireweed. The flowers are tiny and white, barely noticeable, but the weed is easily confirmed once its twin seed pods appear — small paired capsules that give it its name.
When crushed, the foliage has a distinct, sharp odour, which can help with identification. A close relative, wart cress (Lepidium squamatum), looks similar but has single, warty pods rather than pairs.
Why It’s a Problem in Lawns
Twin cress thrives in bare patches, compacted soil, or areas damaged by drought or foot traffic. Once it spreads, its rosettes crowd out new grass seedlings and can survive low mowing heights.
It can tolerate some selective turf herbicides, so light infestations that are ignored often return. In lawns, it gives a weedy, uneven look — particularly over winter and early spring when cool-season grasses slow down.
Control in Home Lawns
Twin cress is easiest to control while small and actively growing.
Best control methods:
- Physical removal: Hand-pull or lightly hoe out rosettes before they spread. They have shallow roots and are easiest to remove when the soil is moist.
- Chemical control: Use selective turf herbicides containing MCPA, dicamba, or picloram/triclopyr (NZLA Gold). Apply early — ideally before the plant flowers or sets seed.
- Timing: Treat in spring or early autumn when new seedlings are emerging. Older plants become more tolerant and harder to kill.
- Cultural control: Keep the lawn dense and healthy through regular feeding, aeration, and overseeding bare patches. Twin cress can’t compete in thick turf.
Prevention Tips
- Reseed thin or bare soil quickly after renovation or winter damage.
- Avoid over-watering or compacting the lawn.
- Maintain regular mowing at a moderate height to encourage dense grass growth.