On 10/9/2011 5:29 PM, Bob Hobden wrote:
"KEPPY" wrote
My lovely blue hydrangea has gradually over 5 years changed its colour
to a mauvy dirty pink with purple tinge.

I understand i can bring the blue colour back by using acidic
fertilizers..... What best choice products do you recommend from a uk
garden centre or maybe from B&Q Also what product would give the
quickest result.

I know pure peat is acidic but i dont wish to use peat even if it was
available in the stores.

The problem is that in alkaline soil they cannot take up the aluminium
salts they need to remain blue as they are locked up with other salts.
Try watering with Sequestered Iron and/or spreading coffee grounds
around the plant, these should help to acidify the soil.
Think I've seen an article on such in The Garden magazine recently.

Aluminium sulfate works well.