Last year, I noticed a Penstemon in a pot outside was limp every day, and when I found the ants' nest, I repotted it (the Penstemon, not the nest). This year, I was too late to save a Magnolia stellata outside, and in the conservatory, I've had to repot a palm, some Meconopsis horridula seedlings, I've lost a Passion Flower, and I'm currently trying to rescue a Pomegranate but the leaves keep falling off.

When I tip the plants out of the pots, they have good root systems. They don't seem able to absorb the water. Do ants produce some sort of chemical which can do this?

I have a sacrificial pot of earth in the conservatory now, ready to empty every so often to try and keep the ants away from my precious plants.

Can anyone tell me what's happening - and how to stop it?

I'm not sure what the ants are doing in my conservatory, though. The nests are in pots, not on a particular type of tree, so they aren't killing species which aren't useful to them. Perhaps it's some sort of instinct, and given the chance, they'd nest in all the pots and kill all the plants. I'm not keen on that idea.

The plants seem to like the soil (apart from the ants) as it is, so I'd rather not make it more alkaline. Perhaps I should put a bit of chalk in all the pots in future. I don't know what would deter the ants but not affect the plants.

You should go into the composting business by getting all the organic waste available locally and spreadng it out over the area affected. Outside will do. Water the area with your grey waste water it will be worth arranging that anyway in a dry sandy soil.

If you dig the soil out annually you will have the richest topsoil imaginable. You will have to treat it to remove the ants. I don't suppose there is a market in it though.

I mentioned the sandy soil as I know ants prefer an easy life. It isn't very sandy, just more sandy than chalky. None of my plants are potted in the soil, they are all in a mixture of JI and multi-purpose compost. I do have ants outside under paving slabs, but they don't cause any problems there. The conservatory isn't indoors, it's more a greenhouse attached to the house. The soil in the conservatory border also has the compost mixture in with the soil. Oh, and I don't have greenfly in the conservatory, either, just outside, where there are black ants. It's red ones in the conservatory.

If it was just too much drainage and lack of water, the plants would have recovered when I repotted them, wouldn't they? I'm still hoping the pomegranate will recover. I repotted it, and put chalk in the pot as well. The Passiflora had beautiful roots, but hasn't recovered.

I was looking for an explanation for something that isn't normal, and the acid thing seemed plausible.