I'm surprised if its got mildew - for one thing, you can't usually see it because the plants hairy and grey... mildew is a passing thing, easily treated by spraying with a fungicide or a mixture of 1 part milk to 9 parts water in a sprayer.

Hello! I agree with bamboo, and have a thought about drainage ... stachys (lambs' ears) seem to do better in well drained gritty soil. I have planted these in places where rosemary or lavender were not wanted, as they are already in other parts of the garden. Could be an answer to the surprising mildew?

Thanks Bamboo and Avkg47. I guess I could try the milk/water combo - I'd forgotten that. It's got to be whole milk hasn't it?

Yes, the soil isn't all that well drained, it's a bit clayey though it's been very dry over summer and that's when it started to show up. I've had powdery mildew on borage and calendula in more or less the same position in the past, so I guess the conditions favour it although everything else in the bed is fine right now.

I can't remember whether it has to be full fat milk - certainly that's the belief held generally, but whether that's what the tests used I really can't recall. I shall try it with skimmed milk next year to see if that works - pretty sure semi skimmed would be fine.