Will blue hydrangeas stay blue?
Then, how do you keep blue hydrangeas blue?
To encourage blue hydrangea flowers, grow the plant in soil that has a pH of 5.2-5.5. If your soil is more alkaline, you can lower the pH by applying Soil Acidifier at the rate specified on the package. Soil pH can also be lowered (more gradually) by applying an acidic organic mulch, such as pine needles or pine bark.
Likewise, do coffee grounds make hydrangeas blue?
If you're growing hydrangeas, use coffee grounds to affect their color. Coffee grounds add extra acidity to the soil around hydrangeas. On a chemical level, this increased acidity makes it easier for the plant to absorb naturally occurring aluminum in the dirt. The effect is pretty blue clusters of flowers.
Ericaceous Compost is ideal. So, to make sure your hydrangea stays really blue add Vitax Hydrangea Colourant, a powder containing aluminium that you can mix with the growing medium when you plant. You can also mix a little into the soil surface each spring and add it to the can when you water your plant.