Changing Hydrangea Color
Learn how to change the color of your hydrangea flowers to blue, pink or purple
The color of a hydrangea can change dramatically, and sometimes they even exhibit multiple colors on the same shrub. Photo by: Ulrich Doering / Alamy Stock Photo.
Flower color can be changed only on specific species of hydrangea, mainly those related to H. macrophylla or H. serrata. The common thought is that flower color is related to the pH of the soil. However, as Michael Dirr explains in his book Hydrangeas for American Gardens, the color is not determined by the pH, per se, but the amount of aluminum a plant can access in the soil — which is determined by pH and phosphorus levels.
A lower pH allows aluminum to be soluble and absorbed by plants (unless phosphorus is high), and the flowers tend to be blue. A higher pH locks up the aluminum and the flowers tend to be pink. Shades of cream to green can also be seen when blooms first open, and tones can change as flowers age.
Tip: Find out your soil's pH by using a 3-in-1 soil tester.
Here’s how you can adjust your soil to affect the bloom color:
- Soil pH below 6.5 = Blue
- Soil pH above 7.5 = Pink/purple
- Soil pH 6.5 to 7.5 (neutral) = Purple, or both blue & pink
- To make sepals bluer, add aluminum sulfate to soil and maintain low levels of phosphorous, moderate levels of nitrogen, and high levels of potassium.
- To make sepals pinker, add garden lime to soil plus maintain high levels of nitrogen and low levels of phosphorous.
- This should be done well in advance of flowering, in autumn and again in early spring. It may take a couple of years to see the full effect. Soil amendments take effect on the developing buds, not flowers that have already formed and bloomed.
Can coffee grounds be used to change the color of hydrangeas?
Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. However, it's best to use aluminum sulfate, a proven method for changing flower color.
Can eggshells be used to change the color of hydrangeas?
Similar to coffee grounds, some gardeners say crushed eggshells may work. However, it's best to a proven method of raising the pH, such as applying garden lime.
Can I make blue hydrangeas with vinegar?
Some gardeners may add vinegar to their watering can to change the acidity of their soil and turn their hydrangeas blue. However, vinegar can be harmful to local wildlife and is not a long-term solution for blue hydrangeas, so we don't readily recommend this technique.
