How to Change Hydrangea Flowers From Pink to Blue (or Vice Versa)

Not all hydrangea flowers can change color, but, if you start with the right variety and expose it to the right conditions, it is possible to change some flower colors from pink to blue or blue to pink. I have provided step-by-step instructions below.

Not sure what type you are growing? See How to Identify Your Hydrangea to figure it out.

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How to Change Hydrangea Bloom Colors

Can you change the color of hydrangea flowers from pink to blue or blue to pink?

Yes. But, it will depend on a few things.

• Start with the right variety.
• Not all hydrangeas flowers can change color but some Bigleaf (Hydrangea macrophylla) and Mountain (Hydrangea serrata) can.
• With those varieties, start with plants with medium or light pink or blue flower color values.
• Deep red and blue colors will not change. White and green flowers will not change.
• To work, you will adjust the soil pH level and control the availability of aluminum in the soil.
• For long-term results, this mean growing the hydrangea in a container, not in the ground. I’ve listed instructions (below).

Following these tips, your hydrangea flowers (known as sepals) will gradually change color.

It may take a year or more depending on the original soil pH level.

Also, it’s easier to shift pink flowers to blue than blue to pink.

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Contents

• Hydrangeas That Can Change Color
• Color Changing Folklore
• How to Turn Pink Hydrangeas Blue
• How to Turn Blue Hydrangeas Pink
• Resources

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Hydrangeas That Can Change Color

Big Leaf Hydrangea

Mountain Hydrangea

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How to Turn Pink Hydrangeas Blue

To do this, grow the plant in a container and lower the soil pH level to 5.6 by adding aluminum sulfate.

1Choose the Right Type of Hydrangea

Start with Bigleaf (H. macrophylla) or Mountain (H. serrata) hydrangeas with medium or light pink or purple flowers.

2Grow in a Container

Grow the hydrangea in a container. This makes it much easier to control the growing conditions long-term. Trying to change the pH of garden soil is a lifelong battle and not worth the effort.

3Monitor Your Soil pH Level

Measure your soil pH level to gauge where you’re at and how long it may take. It’s a gradual process and you can’t push it without harming the plant. At 5.6 or lower, the shift to blue becomes visible.

Options: use test strips like these ones: Garden Tutor Soil pH Test Strips. Another brand is Fisherbrand Plastic pH Indicator Strips.

If growing in the ground (not recommended because results are not sustainable), another option is to contact your  local university extension office or lab that does soil tests to find out the known range for your areas or lookup aerial pH maps.

You could also use physical clues: if hydrangeas stay blue in your garden, that’s a good indication the soil pH is right where you want it.

4Use a Good Potting Mix

Use a good commercial potting mix suitable for shrubs and a low phosphorus-high potassium fertilizer (25-5-30), otherwise the phosphorus will lock up the aluminum.

5Add Aluminum Sulfate If Needed

Water the plant deeply (to avoid burning roots with next step) and then apply an application of aluminum sulfate Al₂(SO₄)₃, also called powdered alum.

You can find this online or at a plant nursery. There are also similar products for this purpose at plant nurseries: Color Me Blue or Color Me Pink.

The sulphur (sulfate) will bring the pH level down, making the aluminum available to the plant but it is a slow process taking months or longer.

Your product should have instructions. Otherwise, do this:

• For longest lasting-results, use a half-application (e.g. 1.5 teaspoons aluminium sulfate in one gallon of water) in fall and again at bud break in spring.
• Repeat annually as needed.
• Always check the package for precautions and instructions.

Alternately you can do just one application per year.

Either way, more is not better: too much aluminum will kill the plant. And each plant has a limit to how blue it will get.

6Take Photographs

Photograph your plant at the start or match the color to paint chip and check progress over the next year.

Once the pH level is lower than 5.6, the color change becomes visible.

How to Turn Blue Hydrangeas Pink

To do this we will grow the plant in a container and make the soil pH more alkaline by adding lime.

Use garden lime (calcium hydroxide, Ca(OH)₂) to make the soil more alkaline. Your product should have instructions for correct application amounts.

This will stop the plant’s ability to absorb any aluminum present. Without aluminum, the color shifts to pink.

• Pink= Aluminium not available / alkaline pH level (6.5 or higher).
• Purple = Some aluminum available + pH between 5.5 and 6.5.
• Blue Flowers = Aluminium present + acidic pH level (5.5 or lower).

Resources

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Read More

• Role of aluminum in red-to-blue color changes in Hydrangea macrophylla sepals
• Proven Winners – Blue Hydrangeas
• Proven Winners – Hydrangeas Demystified
• Soil Acidification: How to Lower Soil pH

It’s an interesting plant! Let me know how your color change goes.

~Melissa the Empress of Dirt ♛