Slowly but surely, what’s left of my untended lawn is being overtaken by a small weed with fan-shaped leaves. It reminds me of a tiny Lady’s Mantle. What is it, and is there any hope of getting rid of it without herbicide?
Your description sounds like Aphanes australis, whose common name is slender parsley-piert. The common name derives from the plant’s leaves which resemble parsley, and the French ‘perce-pierre,’ meaning ‘break (or pierce) stone.’ It thrives in dry, exposed, or barren soils. North Carolina State University’s Turf Center describes cultural control methods:
“Winter annual broadleaf weeds germinate in the fall or winter and grow during any warm weather, which may occur in the winter, but otherwise remain somewhat dormant during the winter. They resume growth and produce seed in the spring and die as temperatures increase in late spring and early summer. They quickly invade thin turf areas especially where there is good soil moisture. Shade may also encourage growth. Many have a prostrate growth habit and are not affected by mowing. A dense, vigorous turf is the best way to reduce the encroachment of winter annual weeds. First, select adapted turfgrass cultivars for your area and then properly fertilize, mow, and water to encourage dense growth.”
It sounds like lawn renovation might be a good idea. If the parsley-piert has intense competition from a happily growing lawn, it will not thrive. Seattle Public Utilities has good resources on lawn care.