some varieties are always blue despite the compost. So do you know which variety you have? Neutral or slightly acidic soils are best and you can get specialist 'food' for them at the gc if that helps.

If its Hydrangea macrophylla/mophead or lacecap type, use a mix of 50/50 ericaceous potting compost and John Innes No. 2 or 3. This type of hydrangea will remain blue in more acidic soil conditions.

Aluminum Sulfate will keep hydrangeas blue. It's a soil acidifyer and should be available at the local garden center.

Hydrangeas have the potential to get 8'x8' and they suck up an immense amount of water. Use the biggest pot/tub you can find.

The plant is a lace cap, called Zorro. Thankyou for all the info.