Gardening Q&A: How do I get rid of my perennial weed?

The experts at the RHS answer your gardening questions...

Question: I have a perennial weed that comes up every year, with a rounded leaf and small yellow flowers. It is growing between a clump of astrantias. Should I dig up the clump and try to separate the weed, or is there a spray I could use? My garden is open for the NGS in June and the astrantias were a talking point last year.

Answer: Your brief description tells me you have a problem with the lesser celandine, Ranunculus ficaria. Its redeeming feature is dying away in summer, but in early spring it can be a really prolific spreader, by seed, bulbils (in leaf axils) and by root tubers that break when you try to dig them up. There is a product called Roundup Gel, which you apply carefully to the leaves when they are in full growth. The chemical moves to the roots to kill them, but will not affect other plants. Apply in early March and again after flowering so the plant takes the chemical down as it dies back for summer. You won't know until next spring whether you have been fully successful and it may need several years of treatment to fully eradicate.

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