Go from pink to blue or vice versa, with a little bit of know-how
Imagine a row of hydrangea bushes with technicolor blue or pink blossoms. Along with adding vibrant color to your property, these flowering shrubs will provide the makings of dramatic, homegrown flower arrangements.
Fortunately, it’s relatively simple to perform a gardening magic trick and transform these flowers from blue to pink or purple. The secret is changing the pH level of the soil, which, over time, affects how much aluminum the plants absorb. Read on for a how-to.
Project difficulty score: 1/5—Simple project; big impact.
Time needed to complete: Several weeks to several months
Materials You’ll Need:
Soil pH Test Kits
Ground Lime or Garden Sulfate or Aluminum Sulfate
If you want to learn how to change hydrangea colors, you need to buy the right cultivars. First, decide on a color, whether blue, purple, pink, red, or white.
Then, keep these facts in mind when selecting plants to buy:
Not all types of hydrangeas change color. Look for lacecap and big leaf varieties and avoid plants with white flowers since their blooms will remain white. Red (very pink) varieties also tend to keep their color.
If your goal is blue, seek out plants with "blue" in their names, like “Let's Dance Blue Jangles.”
Don’t assume plant blossoms will remain the same shade once planted—their hue depends on the state of the soil.
Consider growing hydrangeas in pots since it will be easier for you to control the soil and blossom color. If you plant in the ground and your goal is blue blooms, situate plants away from concrete paths or patios. Concrete often contains lime, which can make flowers turn pink.
Since adjusting soil pH can make it difficult for certain plants to absorb nutrients, situate hydrangeas in their own bed. Or surround them with varieties that aren’t sensitive to soil pH level.
"Amending the soil right after replanting can stress these plants, compromising their health,” says Tara Dudley, owner of Plant Life Designs. “Wait a season to adjust the pH if you have recently transplanted hydrangeas to the ground."
To get a sense of the soil you’re dealing with, perform a pH test in the late fall or early spring. Either purchase a test kit or send a soil sample to your county extension services.
Now it’s time to amend the soil accordingly. Here are the key principles:
More acidic soil allows hydrangea plants to absorb more aluminum, which helps them turn blue or bluish.
More basic soil prevents hydrangea plants from absorbing aluminum, which helps them turn pink.
If you want your hydrangeas to turn blue, you need to lower the soil’s Ph level, or make it more acidic. Do this by adding a soil acidifier, such as garden sulfur or aluminum sulfate. Following the product’s instructions, spreading it evenly in the soil around the plants. Water well. Repeat every two months.
Alternatively, you can use a 25-5-30 lawn fertilizer or spread coffee grounds, citrus peels, grass clippings, leaves, peat moss, or pine needles in the soil. Either way, irrigate with water that’s not hard since hard water can raise the pH level.
If your goal is pink flowers, raise the soil’s pH level, or make it more basic (less acidic). You can do this by adding ground lime, 25-10-10 fertilizer, or crushed eggshells to the soil around the plants.
If you use ground lime, take care to follow the package instructions and treat with the right amount. Too much can cause hydrangea leaves to yellow. Water well. Then reapply repeatedly.
To determine the right amount of product to use for blue, pink, or purple, follow package instructions and consider these pH target levels for various hues:
Bright blue: 4.5
Muted blue: 5
Violet blue: 5.5
Purple or both blue and pink: 6-6.5
Pink: 7.0 or higher
Generally, it takes several weeks to several months for hydrangeas to change color. Often, the blooms will look cream or green initially and gradually transition to another hue as they age.
Even after they do, they won’t remain their new color unless you continue to test and then amend the soil accordingly during the growing season.
This task is an ideal DIY because it’s so simple. However, if you’ll be out of town during the growing season, ask a landscaper in your area to handle this process for you.
No, the level of phosphorus in the soil also impacts the hue of these blooms. A higher phosphorus level will help make blossoms pink. A low phosphorus level will help make blossoms blue.
Hydrangeas are the only plant whose blossoms change color while growing thanks to soil conditions.
Zones six through nine are ideal for hydrangeas, according to the U.S. Department of Agriculture. However, it does depend on the variety of hydrangea.
Fall is ideal, followed by early spring.
