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Home arrow The Daily Dirt arrow Thursday Tips & Techniques: The Color of Hydrangeas
Thursday Tips & Techniques: The Color of Hydrangeas Print E-mail
Written by Heleigh Bostwick    Thursday, 21 July 2016
Hydrangea flowers

Hydrangeas are the classic old-fashioned flowering shrub for the perennial garden or foundation plantings. While most of our cultivated hydrangeas aren’t native, they aren’t invasive either (many cultivars have sterile flowers), so I thought I’d take a detour today and talk about big leaf or French hydrangeas (Hydrangea macrophylla)--the ones that have bluish or pinkish flowers, or sometimes a combination of both colors.

The color of the hydrangea flowers is dictated by the presence of aluminum in the soil and only the flowers of the French hydrangea can be made to change color from blue to pink or vice versa. When aluminum is present in the soil, as is normally the case, flowers are bluish in color; however, if the soils are too alkaline the plant is unable to take up the aluminum and the result is pink flowers.

If aluminum is not present in the soil at all, aluminum sulfate can be added to the soil. Once again however, the acidity of the soil must be in the optimal range in order for the aluminum to be taken up by the plants. The optimal range for soil acidity in this case is a pH of 6.0 to pH 7.0. I f soils are too acidic it’s possible to add lime to make them more alkaline and within the optimal pH range.