How to Change the Color of Your Hydrangeas
With many 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 a blue bigleaf hydrangea can turn to pink. According to Ryan McEnaney, the public relations and communications specialist for 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
Now, here's how it works: "Acidic soil, with a pH below 6.0, will promote blue blooms," says McEnaney, "and alkaline soil, with a pH above 6.0, will promote pink blooms." (You can find your soil's pH with a kit you can purchase at your local gardening home center or nursery, or from an online retailer. You'll get a number from 0 to 14.) "If your soil pH is on the extreme ends of the spectrum, you can get even deeper colors," McEnaney explains.
How to Change Color
If you find you have acidic soil—meaning your soil's pH is less than 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. With alkaline soil—meaning you have soil with a pH of 6.0 or more—you can change your plant from blue to pink by adding a soil acidifier or aluminum sulfate, both of which can be purchased at your area garden center.
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," he says. You may have farther to go on the spectrum from acidic to alkaline or vice versa—and you may need more addictive to move the scale.
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.