Did you know?
— Massimo (@Rainmaker1973) April 7, 2026
The color of hydrangea isn't just genetics — it's the soil they grow in.
Specifically, soil pH affects the availability of aluminum, which in turn influences flower color. pic.twitter.com/OgYRPrshLL
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How it works
The flower color depends on soil pH and aluminum availability:
-
Acidic soil (low pH, below ~6)
→ Aluminum becomes available to the plant
→ Flowers turn blue -
Neutral soil (around pH 6–7)
→ Mixed availability
→ Flowers may be purple or bluish-pink -
Alkaline soil (high pH, above ~7)
→ Aluminum is “locked away” and unavailable
→ Flowers turn pink
Why aluminum matters
It’s not just the pH alone — the key is a soil chemistry interaction:
- In acidic conditions, aluminum dissolves and is absorbed by the plant
- Inside the petals, aluminum reacts with pigments, producing blue tones
- Without aluminum, the natural pigment appears pink
Important note
- This effect mainly happens in bigleaf hydrangeas (Hydrangea macrophylla)
- White hydrangeas do not change color
- Some varieties are bred to stay pink or blue regardless of soil
A fun gardening trick
Gardeners sometimes:
- Add coffee grounds or sulfur → to make soil more acidic (bluer flowers)
- Add lime → to make soil more alkaline (pinker flowers)
