How to Change Hydrangea Color

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.

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.