How do pennies make hydrangeas blue?

Chasing the Blues. If you yearn for blue flowers, acidic soil — not pennies — can bring the color you seek. Lower your soil's pH to free aluminum and prompt bluing in hydrangea blooms. For gradual results, water in 1/2 cup wettable sulfur powder per 10 square feet once each year.

Then, what do I add to the soil to make my 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.

Do hydrangeas need ericaceous soil?

On soils that have a fairly neutral pH it is possible to bring this change about by applying a blueing agent that contains aluminium sulphate to the soil. These can be found online and in most garden centres. It is possible to achieve the same effect by growing Hydrangeas in pots of ericaceous compost.

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