To start, you’ll need a pH reader to measure your soil. If you want to increase the soil’s acidity and turn your hydrangeas blue, you need to add garden sulphur near the base of the plant.
Some say applying coffee grounds to the soil also works. In that case, it needs to be fresh coffee grounds or brewed coffee – because those are the most acidic – and it needs to be applied regularly throughout the entire growing season.
To achieve pink hydrangeas, on the other hand, use garden lime at the base of the plant. That stops the aluminium from being available to the plant, keeping it from turning too blue.
In either case, remember to be patient. It can take months for the colour to change.
