How to Change Hydrangea Color

Find the secret to changing the hue of these popular blooms.

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L.A. Dreamin' Hydrangea

L.A. Dreamin' Hydrangea

The lush blooms of 'L.A. Dreamin'' allow myriad shades of pink and blue to coexist on the same plant, whether you adjust the alkalinity of the soil or not.

The lush blooms of 'L.A. Dreamin'' allow myriad shades of pink and blue to coexist on the same plant, whether you adjust the alkalinity of the soil or not.

Hydrangeas are wonderful performers in the garden. Even better, they are the mood ring of plants, apt to change color depending upon soil conditions. Here we’ll tell you how to change the color of the flowers, if you want a different palette in your garden.

How to Change Hydrangea Color:

Unlike most flowers, lacecap and mophead hydrangeas (H. macrophyllas) can change colors. Eighteenth-century gardeners were the first to notice this, and experimented by burying rusty nails, pouring tea or even chanting spells around their plants.

Hydrangea Endless Summer 'The Original'

Hydrangea Endless Summer 'The Original'

Many gardeners think hydrangeas need deep shade, but many prefer morning sun and afternoon shade, especially in hot climates. Endless Summer hydrangeas are re-blooming shrubs that like at least 6 hours of sun in zones 4 to 5a, with dappled afternoon shade. In general, hydrangeas can take more sun, the further north you live.

Photo by: Photo by Lynn Coulter

Photo by Lynn Coulter

But it’s the pH of the soil that determines flower color—specifically, whether or not the hydrangeas are taking up aluminum from the soil. If the flowers are pink, the plant is getting aluminum. If they’re blue, it isn’t. You can control the color by altering the pH.

Start by using a purchased soil test kit to find your pH. You can also send a soil sample to many county extension services for testing; Check with your local office to see if they offer this service.

Generally speaking, acidic soil, with a pH lower than 6.0, yields blue or lavender-blue hydrangea blooms. Alkaline soil, with a pH above 7.0, promotes pinks and reds. With a pH between 6 and 7, the blooms turn purple or bluish-pink.

To lower your pH, add garden sulfur or aluminum sulfate to your soil. To raise the pH, use ground lime. Follow the directions on the product you use, and retest your soil to make sure the pH is in the range you want.

You may have to reapply the garden sulfur or lime several times, and it may take several months for a change to occur. Don’t be disappointed if the color stays the same. Some selections resist changing, and white hydrangeas tend to remain white.

And don’t be surprised if the hydrangea you bought in a foil-wrapped pot changes color when you plant it outside. Remember: the pH of the soil determines the bloom color.

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