How to Change the Color of Your Hydrangeas

With many garden flowers, what you buy is what you get: Red roses are red roses; yellow gerbera daisies are yellow gerbera daisies. But bigleaf hydrangeas are different. If you purchase a pink one, you can change it into a blue one—and if you have a blue hydrangea, you can turn it pink.

According to Ryan McEnaney from Bailey Nurseries, bigleaf hydrangeas' changing colors are attributed to the pH of the soil they are grown in—and luckily, there are easy things you can do to manipulate your soil's acidity if you prefer one color over another.

Check the Variety

You can only change the color of a bigleaf hydrangea. "Other types of hydrangea cannot do this," McEnaney warns. So, if you're purchasing a hydrangea for the first time and want to change its natural hue, make sure you buy a bigleaf variety, he says.

Check the PH

You need to know what the pH of your soil is. You can find your soil's pH with a kit purchased at your local gardening home center or nursery or from an online retailer. You'll get a number from 0 to 14.

Now, here's how it works: "Acidic soil, with a pH below 6.0 will promote blue blooms, and alkaline soil, with a pH above 6.0, will promote pink blooms," says McEnaney. "If your soil pH is on the extreme ends of the spectrum, you can get even deeper colors," McEnaney explains.

How to Change Your Hydrangea's Color

In either direction you take your plant, the amount of additive needed depends on how far from basic soil—a pH of 6.0—you are, McEnaney says. You may have further to go on the spectrum from acidic to alkaline or vice versa—and you may need more additives to move the scale.

From Blue to Pink

If you have acidic soil—meaning your soil's pH is under 6.0—and you would like to change your hydrangeas from blue to pink, add garden lime, which is found at most local nurseries, or wood ashes to your soil, McEnaney says. This will make your soil more alkaline.

From Pink to Blue

With alkaline soil—meaning you have soil with a pH of 6.0 or more—you can change your plant from pink to blue by adding a soil acidifier or aluminum sulfate, both of which can be purchased at your area garden center.

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How Long Does It Take?

Don't expect instant results when changing your hydrangea's color. It can take several weeks or even an entire growing season for color changes to show. For best results, apply soil additives in early spring, before buds begin to form. That gives your plant time to absorb the acidity as the blooms develop.

Don't Forget to Fertilize

No matter what you do, don't forget to fertilize your hydrangea. Additives such as garden lime and soil acidifier do not replace fertilizer, McEnaney says. "They are separate additives with different purposes, so be sure to follow fertilizing instructions in addition to the color-changing treatment," he says, to ensure you have both the brightest and healthiest blooms.