Why do hydrangeas change colour? The trick to use if you want to change bloom colours

If you have more alkaline soil and therefore are destined to have pink hydrangeas, but would like blue flowers you should make the soil more acidic.

You can do this by increasing the presence of aluminium.

Add elements such as pine needles, compost, coffee grounds or aluminium sulfate to help make soil more acidic over time.

Bear in mind, you must undertake to change your soil’s pH gradually – it can take up to a year for it to work.