How to Turn Hydrangeas Blue or Pink

Hydrangeas come in beautiful shades of white, blue, pink, and green. Unlike other flowering shrubs, hydrangeas have the unusual ability to change their flower color. The determining factor of hydrangea color is the level of soil acidity: in alkaline soil, hydrangea flowers turn pink, while in acidic soil, they turn blue.

If the soil is not naturally alkaline or acidic, you can gradually amend it to change the flower color of your hydrangea. However, not all hydrangea varieties can change their flower color from pink to blue and vice versa. Learn how to make your hydrangeas blue or pink below.

What Determines Hydrangea Color

Two interdependent factors determine whether the hydrangea blooms pink or blue: the availability of the micronutrient aluminum to the plant and the soil pH.

The more aluminum the plant can absorb from the soil, the closer the pigment molecules in the bracts move together, thus turning the color blue. When less aluminum is absorbed, the molecules in the flower move apart, causing it to turn pink.

The amount of aluminum available to plants is determined by the soil's pH level. This is because aluminum is more soluble in soils with a lower pH level (acidic) as opposed to those with a higher pH (alkaline). Although most soils contain enough aluminum, it may not be available to the plant if the soil pH is above a certain level.

Here's how soil pH affects the hydrangea flower color: 

• Acidic soil (pH 5.0-5.5): Blue flowers
• Neutral to alkaline soil (pH 5.5– 6.5): Mauve, purple, or a mixture of blue and pink flowers
• Alkaline soil (pH 6.5-7.0): Pink flowers 

Which Types of Hydrangeas Change Colors

Before you take any steps to change your hydrangea colors, you need to identify what kind of hydrangea you have.

Of the many different varieties, only bigleaf hydrangeas (Hydrangea macrophylla), also known as French, mophead, or lacecap hydrangeas, and mountain hydrangeas (Hydrangea serrata) can change the color of their flowers.

The color of oakleaf hydrangeas (Hydrangea quercifolia) and peegee hydrangeas (Hydrangea paniculata) with white or cream-colored flowers cannot be changed.

How to Change Hydrangea Color 

1. Test the Soil

   Obtain a soil pH testing kit from a garden center or your local Cooperative Extension Office. Perform the test according to the directions to determine the pH of the soil. Analyze the results and decide if you need to increase or decrease the pH to achieve your desired flower color.

2. Select Your Soil Amendment

   Choose your soil amendment based on the current pH level and your desired color.
   

   • To turn the flowers blue, lower the soil pH (make it more acidic) by adding aluminum sulfate or wettable sulfur to the soil.
   • To turn the flowers pink, raise the soil pH (make it more alkaline) by adding limestone to the soil.

3. Add Amendment to the Soil

   Granular Method (any time of year): Apply the product around the base of the plant and work it into the soil with a rake or a cultivator.

   Liquid Drench Method (March, April, May): Dissolve 1 tablespoon of aluminum sulfate for blue flowers or 1 tablespoon of hydrated lime for pink flowers in 1 gallon of water. Drench the soil around the hydrangea with this solution, taking care not to spill any on the leaves.
   

   Warning

   Do not measure amendments to the soil based on guessing or estimating. Adding too much or too little may harm your hydrangea and surrounding plants. Please follow the directions carefully so you know exactly how much product to use based on soil type and current pH level as tested.

Additional Methods

There are some organic methods you can try to get your hydrangeas to turn blue or pink.

Coffee Grounds for Blue Hydrangeas

Some gardeners claim success in changing the color of their hydrangeas with coffee grounds. Leftover grounds will increase the acidity of your soil therefore turning the blooms blue. Sprinkle them in late fall and work them into the soil. Repeat the process whenever you fertilize.

Egg Shells for Pink Hydrangeas

Crushed eggshells may be one way to get your hydrangeas to turn pink. Add them to your soil and mix in well. As the eggshells slowly break down, they will reduce the acidity of your soil. Aluminum will be harder to absorb and your blooms are likely to turn pink over time.

Maintaining the Soil pH

Have patience after amending your soil. The soil pH change can take several weeks, months or even up to a year to take effect and show in the flower color of your hydrangeas. The bigger the change you need to make in the soil pH to get the desired flower color, the more difficult and lengthier the process will be.

Continue to test the soil during this time and further amend if necessary. Changing the pH is a gradual process that does not happen all at once. Even if you can get the soil to the desired pH, it will naturally revert to its original pH as time goes on. This can make changing your hydrangea color feel like an uphill battle. If your soil is naturally alkaline or naturally acidic, you may want to learn to love the color you have.