This has confused me a little, it,s usually the pink ones that turn purple if they,re grown in an acid soil, but if you wanted to keep it blue I would plant it in ericaceous compost, or give it a dose of aluminium sulphate, or sequestrene every year, Derek.

Well it was a beautiful pale blue and I assume it was the compost I used which I didn't even think about and it turned a ghastly purple colour within weeks. I have cut all the flowers off (I know they are supposed to stay on to protect the plant during the winter) and its doing very well health wise. I have something in the garden shed to water in so I might try repotting it and using that. Thanks for your input.

I,ve a big one in the garden with pinks and mauves, its the soil.....we were at a nt garden recently and different parts of the gardens had varying hydrangea colours.....some gorgeous blue in the acid areas and one amazing white, I think ( but am not sure) that whites the only one not affected by the type of soil

You should have planted in ericasious compost but you must have used a compost containing lime which locks up the magnesium and iron, hence the shrub is turning mauve and eventually red or pink. John Innes ericasious compost and watering with rain water if you are in a hard water area. As advised, if grown in a pot it will eventually wash away nutrients so you will have to add some regularly.

Thank you. I always use rainwater from my water butt and haven't used tap water since long before the hose pipe ban. I will have to get some John Innes. I don't particularly like hydrangeas - I've given one away and uprooted another. I still have 3 - white, pink and this mauve one. I only want to keep this as my daughter bought it for me.