Published on 02/28/12

Aluminum is the key to changing hydrangea bloom color

By William G. Tyson

Often purchased as a gift plant, bigleaf hydrangea can be transplanted in landscapes and enjoyed year after year.

Bigleaf hydrangea prefers morning sun, afternoon shade and moist, well-drained soil. It will grow in locations with afternoon sun, but will probably wilt and need more supplemental watering.

They don't like full sun

Do not expect the plant to take full sun. The large leaves of hydrangea result in more water loss in the heat of summer. So, hydrangeas perform best when given a break from the sun.

Bigleaf hydrangea can be easily grown in containers and make an excellent patio plant. An advantage of growing the plant in a container is that it can be moved indoors on a cold night.

Also called French, Japanese or snowball hydrangea, the plant is known for its flower colors that can be changed from pink to blue or from blue to pink by adjusting the soil pH. The color variation is due to the presence or absence of aluminum compounds in the flowers. If aluminum is present within the plant, the flower color will be blue. If it is present in small quantities, the color will be in between, or violet, and if it is absent, the flowers will be pink.

Aluminum affects bloom color

Soil pH indirectly affects flower color by affecting the availability of aluminum in the soil. When the soil is acidic, pH 5.5 or lower, aluminum is generally more available to the roots. When the soil is neutral or alkaline, pH 7.0 or higher, aluminum levels are decreased.

To gradually change flower color from pink to blue, broadcast one-half cup of wettable sulfur per 10 square feet and water it into the soil. To make the flowers pink, broadcast 1 cup of dolomitic lime per 10 square feet and water it into the soil. Granular products can be applied anytime throughout the year. However, it takes patience to change hydrangea flower colors, as it can take a year to see a noticeable change.

A quicker way to change flower color is through liquid soil drenches applied in March, April and May. To make the flowers turn blue, dissolve 1 tablespoon of aluminum sulfate in 1 gallon of water. To make the flowers turn pink, dissolve 1 tablespoon of hydrated lime in 1 gallon of water. Drench the soil around the plant with the solution. Avoid getting the solution on the leaves.

It is not hard to change hydrangea flower color; simply decide which method best suits you. With the right care and materials, you can have hydrangeas of your color choice.

William Tyson is the UGA Extension coordinator for Bulloch County.

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