It's still accessing aluminium in the soil, despite your lime application. Some places say to apply dolomite lime several times a year, others say apply lime 6-9 months before the flowers are due to appear. The risk with over application is reducing the plant's ability to access certain nutrients, and none of the research I've done gives a rate of application and a specific timetable, so its all a bit hit and miss. The only way to be absolutely sure what colour it will be is to grow it in a pot, I'm afraid.

RHS recommend "If you wish to enhance red or pink flowers, apply a dressing of ground limestone or chalk at a rate of 75-100g per sq m (2-3oz sq yd) in winter."

It's worth checking the specific pH requirements of the variety. I'd choose a white hydrangea to get over the nonsense of them changing colour (although I did buy a very pale pink one a few weeks ago as it was in the £1.99 bargain bucket at a nursery)

It's also clear from reading on line in various places that these types of hydrangea may even change colour from year to year, and even if they don't do that, they can take up to 3 years to settle to a colour. Even planting near conifers has an effect - blimey, what a fusspot...

No idea why this question appears twice.

The strange thing is its been a lovely deep red for eight years with nothing except a seaweed mulch. It seems to have been adding the lime that's caused the problem so I just don't understand it. I feel more like neutralising the lime than adding more! I'm sure I didn't overdo the lime, it was more or less a tentative excperiment, which i won't be repeating!
Its too big to go in a pot Bamboo.
Urbanite I can't check the requirements of the variety - it was here unlabelled when we moved in. I do have a white one already - Annabel. Hope you enjoy your lovely pink one.

I do appreciate you both answering, and even looking stuff up for me but we don't seem to be any further forward! Just hoping whatever caused it will wear off in time and that this ois one of the ones that can change from year to year!

Well if the lime didn't work go the other way and give it a dose of coffee grinds. After 8 years it could be something environmental - temperature, rain - that just coincided with it setting flower buds. We've had a couple of "wetter-than-normal" years.

We don't usually drink much coffee so I'll have to go begging in a cafe!

Apparently the American coffee shops that don't pay any tax will oblige.

Right - now to find out which ones in our very small town are American...thank you!

In the end I thought a lot and ended doing nothing. This year we appear to be back to red again. |One of life's little mysteries!