There's a little science (and a lot of soil) behind why some hydrangea flowers change color from blue to pink. We break down the basics.
Here’s How to Change Your Hydrangea Flower Color
Published on Jun. 26, 2025
Hydrangeas have a way of keeping gardeners on their toes. One season the flowers are soft pink, the next a vivid blue — or sometimes both, on the same bush. There’s something quietly thrilling about a plant that changes its look without ever leaving the ground. No surprise, then, that gardeners have spent decades trying to decode their color shifts.
If you’ve ever passed a hydrangea in a show-stopping hue and thought, Why doesn’t mine look like that? — you’re in good company. With a little science, a little patience and the right soil know-how, you can guide those colors your way.
Hydrangea not blooming? Here’s what to do.
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Which Hydrangeas Can Change Colors?
“Everybody wants that perfect blue flower,” says Connecticut-based gardening expert Lorraine Ballato. “But changing hydrangea color isn’t a quick trick. It’s more like a process — and one you have to stay on top of.”
Not all hydrangeas are color-changers. The ones you’re looking for are bigleaf (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata). These varieties can shift between blue, purple and pink depending on the pH and aluminum content in the soil.
Other hydrangeas — like panicle, oakleaf and smooth — don’t respond to soil in the same way. “Panicle hydrangeas, for example, naturally age from white to pink or red as the season progresses,” Lorraine says. You can now find pink smooth hydrangea cultivars like Invincibelle Spirit II, Invincibelle Mini Mauvette and Incrediball Blush with flowers that are always pink no matter the soil pH.
How to Test (and Hack) Your Soil
Soil holds the key to hydrangea color because it controls what the plant can actually absorb. It’s less about the flower and more about what’s happening underground. As a general rule:
- Acidic soil (pH below 5.5) plus aluminum = blue blooms
- Alkaline soil (pH above 6.0) = pink blooms
Before you start amending anything, get a baseline. There are easy DIY soil tests available at most garden centers (usually near the register), or you can send a sample to your local extension office or university lab with calibrated equipment that provides a more reliable pH reading. But Lorraine offers a reality check: “Soil test results aren’t always consistent. They’re a guide, not gospel.” The soil can vary throughout your landscape and the soil test results are only as good as the sample taken.
Many garden centers sell pH-only versions, or you can go for a more advanced kit that tests for nutrients like calcium and magnesium. Most involve mixing a bit of soil with water and a powder, shaking it up and comparing the resulting color to a chart. That reading gives you your baseline and helps determine what amendments, if any, you’ll need to shift your hydrangea’s hue.
Manage your expectations. “In places with very alkaline or lime-heavy soil, like much of the Midwest, it can be especially tough to make any real change,” Lorraine says.
How to Turn Your Hydrangeas Blue
To nudge your blooms toward blue, your soil needs to be acidic. If your test shows your soil is too alkaline, start by applying soil acidifiers — products like sulfur, peat moss or acidifying fertilizers labeled for acid-loving plants.
Once you’ve brought the pH down to the right range, apply aluminum sulfate, which not only helps further acidify the soil but also supplies the aluminum your plant needs to produce those rich blue tones. Look for a product labeled specifically for hydrangeas, and follow directions carefully; too much can stress or damage the plant.
“Blue is one of the rarest colors in the flower world, so achieving it takes effort,” says Lorraine. “You can make the soil acidic, but if there’s no aluminum in it, your plant won’t turn blue.” Aluminum is used in small amounts and adding too much aluminum over time can be toxic to the plant. Once again, a soil test is an important place to start.
How to Turn Your Hydrangeas Pink
To raise the pH, apply garden lime (calcium carbonate), also labeled as dolomitic lime. This neutralizes acidity and moves your soil toward the pink-friendly zone. Look for products that specifically mention use with hydrangeas, and follow the package instructions closely.
It is important to follow soil test results as over liming or over acidifying the soil can interfere with the uptake of other nutrients plants need to grow and thrive. It can take many years to undo this change.
DIY and Mulch Myths
Online gardening hacks promise color change with everything from vinegar to coffee grounds, but Lorraine doesn’t recommend it. “These homemade solutions aren’t scientifically supported and can actually harm your plant,” she warns.
Mulch misconceptions are common, too. Pine needles may slightly affect pH over time, but not enough to change bloom color. That hydrangea thriving under a pine tree? It’s likely the soil, not the mulch.
What to Expect — and What Not to Expect
Hydrangea color change doesn’t happen overnight. It can take a full season (or more) to see results, and the process needs ongoing attention. Some gardeners try container growing to speed things up, but Lorraine notes that while containers offer control, they also leach nutrients faster and require more frequent care.
“Apply in the fall, not spring, to give the plant time to absorb the amendments before the next blooming cycle,” says Lorraine. “Then retest the soil in three to four weeks to see if you’re getting closer to your target pH. This isn’t a one-and-done project,” Lorraine says.
And yes, you might see different bloom colors on the same plant. “It all depends on where the roots are. If one side is sitting in more acidic soil, that half might turn blue while the rest stays pink. You’re basically running a live soil experiment.”
Embrace the Hydrangea Color Change Mystery
Hydrangea color change isn’t an exact science, and even the best efforts can yield unexpected results. Lorraine encourages gardeners to enjoy the unpredictability. “At some point, you might just have to learn to love the color you’re getting. Hydrangeas have a mind of their own, and that’s part of the fun.”
About the Expert
Lorraine Ballato is an award-winning writer, speaker and horticulturist. She is the author of the book Success With Hydrangeas and the blog of the same name.
