So last year I bought a blue hydrangea and planted it in a pot. I’ve done everything I was told to in order to keep it blue … this year it has flowered pink!!! Can anyone suggest what I should be checking/doing???
The point of a low ph is in order to make Aluminium available to the hydrangea – Aluminium is the key to making a hydrangea turn blue. So if your soil is the correct ph (5.2-5.5) then you can add aluminium as follows:
Make a solution of 1 tbsp aluminum sulfate per 4 litres of water and feed to hydrangeas (which are at least 2-3 years old) during the growing season. Beware Water plants a lot before application and pour solution on cautiously, as too much can burn the roots!