Planting hydrangeas? Here's how you can change the hues of these beautiful blooms

Hydrangeas are a charming addition to any garden, and what makes them even more fascinating is their ability to change colour based on the soil they’re planted in.

This unique trait allows you to influence the hue of your blooms, creating a customised palette that suits your garden’s aesthetic, or if you’re a fan of only pink or blue hydrangeas, to only plant one colour.

The science behind hydrangea colours

The colour of hydrangea flowers, particularly those of lace cap and mophead varieties (Hydrangea macrophylla), is largely determined by the pH level of the soil.

Simply put, acidic soil (with a pH lower than 6.0) results in blue or lavender-blue flowers, while alkaline soil (with a pH above 7.0) leads to pink or red blooms. If your soil falls in the neutral range (between 6.0 and 7.0), you might see purple or bluish-pink flowers.

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How to change the colour of your hydrangeas

Follow this step-by-step guide:

1. Test your soil

Start by determining the pH of your soil. You can purchase a soil test kit or send a sample to your local agricultural extension service for analysis.

2. Adjust the pH

To encourage blue blooms: If your soil is too alkaline, you can lower the pH by adding garden sulfur or aluminum sulfate. Follow the instructions on the packaging for the best results.

To encourage pink blooms: If your soil is too acidic, raise the pH by incorporating ground lime into the soil.

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3. Be patient

Changing the colour of your hydrangeas is not an overnight process. It may take several applications and a few months to see a difference in the bloom colour. Remember that not all hydrangeas will change colour, and white varieties typically remain white regardless of soil pH.

4. Re-test and reapply

After making adjustments, re-test your soil to ensure it’s within the desired pH range. You may need to reapply the garden sulfur or lime periodically to maintain the correct pH level.