Dear Doctor, I have a chronic case of lemna minor in my water garden and wonder if you have a remedy for me. It completely covers the surface of one of the two 12-foot square ponds; the other, under the constant splash of a fountain, is also affected, but less seriously. Why it has infected us now I don’t know. In forty years it has made occasional appearances and I have netted it off, but this time the problem is serious: it has spread through the clumps of Iris kaempferi that occupy three of the corners.
How am I to clean it out? I could try blasting the clumps with a pressure hose – but thatwould send the tiny plants flying everywhere. I could dig the irises out of the water and try to clean them elsewhere before putting them back. No chemical treatment for duckweed, of course, is available or legal for mere gardeners. And why wouldn’t the pest come straight back next year? I’ve noticed, by the way, that ducks rarely touch the stuff. Nor do moorhens – of which we have an oversupply. Grass carp, I’m told, devour it along with everything else.
An apparent lawn is no substitute for the gleam of water. And I love my floppy irises, some purple, some white, sometimes flowering right up to the first frost. Can you help me, please?