Why do Hydrangeas Change Colour? Unlock the Mystery & How to Adapt them to your Garden

melaniekerr
Oct 15
3 min read

Hydrangeas are famous for their drama. One year they are a brilliant blue, the next they are blushing pink, and sometimes they even surprise you with shades of purple, cream, or green.

But here is the secret: hydrangea colour change is not random. With the right knowledge, you can change hydrangea colours yourself by adjusting your soil pH.

Read on to unlock the mystery and learn exactly how to shift your blooms from pink to blue (or the other way around) and design your garden like a living colour palette.

Why Do Hydrangeas Change Colour?

Not all hydrangeas change colour, but the most popular ones that do are:

Bigleaf hydrangeas (Hydrangea macrophylla)
Mountain hydrangeas (Hydrangea serrata)

The secret lies in your soil acidity (pH) and its relationship to aluminium availability:

Acidic soil (pH below 6): aluminium is absorbed → blooms turn blue or purple
Neutral to alkaline soil (pH above 6.5): aluminium is blocked → blooms shift pink or red

Other types such as Panicle hydrangeas (Hydrangea paniculata), Smooth hydrangeas (Hydrangea arborescens), and Oakleaf hydrangeas (Hydrangea quercifolia) do not typically change colour. They will stay white, cream, or soft green regardless of pH.

How to Change Hydrangea Colour

If you would like to influence whether your hydrangeas bloom pink, blue, or purple, here is how:

Start with a soil test. This tells you whether your garden is acidic, neutral, or alkaline.
For blue hydrangeas: Lower soil pH by adding sulphur or aluminium sulphate. This increases aluminium uptake.
For pink hydrangeas: Raise soil pH with garden lime. This blocks aluminium uptake and encourages warmer tones.
Be patient. Hydrangea colour change can take a full season or longer. It is not instant.
Consider containers. If you want more control, grow hydrangeas in pots so you can fine-tune the soil mix.

Pro tip: Do not over-amend your soil all at once. Gentle, seasonal adjustments are safer for your plants.

Hydrangea Garden Design Tips

Now that you know how to change hydrangea colours, here are some fun ways to use them in your garden design:

Create contrast: Pair a blue or pink hydrangea with a white panicle variety to make colours pop.
Enjoy the fade: Leave blooms on the plant, as they age they shift into antique shades of green, burgundy, or dusty pink.
Mix with texture: Combine hydrangeas with lush foliage plants such as hostas or ferns for extra drama.

Things to Keep in Mind

Before you start adjusting your soil, remember:

Not every hydrangea variety responds strongly to pH changes. Genetics matter.
Extreme changes in soil pH can harm your plants. Go slow.
Weather and growing conditions also affect bloom colour intensity.

Final Thoughts

Hydrangeas are playful, surprising, and endlessly fascinating. They do not just add flowers to your borders, they tell a story in colour. By understanding the link between soil pH and hydrangea colour, you can shape that story and bring new vibrancy into your garden.

So next time your hydrangeas switch shades, do not be puzzled. Know that it is your soil talking back to you.

Ready to Design Your Dream Garden?

If you would love expert guidance on choosing the right hydrangeas (and other plants) for your garden, plus personalised tips for getting the look you love, why not book a Garden Design Consultation with me?