Hydrangeas change colour with the soil. Yours is different from the soil it was last grown in. To make them blue you need to add aluminium to the soil. Good luck.

Thanks

Hi I agree with Linda, but don't be fooled into buying the "special" Hydrangea colourant they try to sell you in garden centres, all you need is sequestrene, or aluminium sulphate once a year, and you will have blue flowers, Derek.