How to Change Hydrangea Flower Colors

I’ve always loved the vibrant colors of hydrangea flowers and when I learnt that the flower colors can be adjusted by manipulating the soil conditions, I was keen to try it myself.

The transformation of hydrangea flowers from pink to blue, or vice versa, is not an instant process, but with a little patience, it’s possible to alter their colors over time. 

In this article I’ll share my tips for changing the colors of your hydrangea flowers.

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Soil pH and Flower Color

Adjusting the pH of the soil affects the availability of aluminum ions, which in turn influences the color of hydrangea flowers. 

To encourage blue colored hydrangea flowers, the soil must be acidic, while a more alkaline environment encourages pink blooms. 

Adding certain substances to the soil can gradually shift its pH in the desired direction. 

I find it rewarding to tweak the soil composition, watch the gradual change of the flower colors, and know that I’ve had a direct hand in their transformation. 

While some people might prefer to let nature take its course, for me, experimenting with the color of hydrangea flowers is a nice way to engage with my garden and create a personalized landscape. 

small blue hydrangea

Understanding Hydrangea Colors

The Science Behind Color Changes

The color variation occurs due to the presence of aluminum ions in the soil, which hydrangeas can only absorb in acidic conditions. 

If they’re accessible, these ions bond with pigment molecules in the sepals, which are often mistaken for petals, and result in the blue coloration.

Lime can be added to increase pH and encourage pink blooms, while applying garden sulfur lowers the pH to favor blue flowers. 

It’s important to adjust the pH gradually and test the soil periodically, as drastic changes can harm the plant.

purple hydrangea flowers

Hydrangea Species and Their Colors

The most well-known hydrangea species for color variation is H. macrophylla, commonly called bigleaf hydrangea

This species includes the mophead variety, with large, round flower heads, and the lacecap variety, featuring flat flower heads with a center core of subdued, fertile flowers surrounded by outer rings of showy flowers.

H. serrata, or mountain hydrangeas, are similar to bigleaf but are typically smaller and have more delicate flowers. 

It’s interesting to note that not all hydrangea species change color. 

For example, white hydrangeas don’t change color with soil pH and are typically grown for their pristine, white blooms.

pink and blue hydrangea blooms

Modifying Soil to Change Hydrangea Color

Altering pH for Blue and Pink Blooms

To achieve blue hydrangea blooms, I make the soil more acidic by lowering its pH. 

For blue flowers, a pH of about 5.2 to 5.5 is ideal. 

To acidify my garden soil, I incorporate garden sulfur or peat moss, which can lower pH over time. 

For a quicker change, you can use aluminum sulfate, which supplies aluminum – necessary for blue coloration. 

Creating pink hydrangea blooms requires a higher pH. 

You can apply ground lime to increase alkalinity, aiming for a pH around 6.5 to 6.8. 

pink hydrangea flowers

Use a soil test kit to help you monitor the pH level of your soil and make necessary adjustments.

  • Acidic soil (lower pH) for blue hydrangeas, add:
    • Garden sulfur or aluminum sulfate
    • Peat moss
    • Coffee grounds or citrus peels
  • Alkaline soil (raise pH) for pink hydrangeas, add:
    • Garden lime or dolomitic lime
    • Crushed eggshells
    • Higher pH water, like rainwater with a touch of baking soda


So there are my tips for changing the color of your hydrangea flowers.

Whether you’re aiming for vibrant pinks, blues, or even purples, understanding the factors that influence hydrangea colors is key to achieving the desired results. 

With the right knowledge and techniques, you can enjoy a captivating display of multi-colored hydrangea flowers, adding a delightful pop of color to your garden landscape.

Are you on Pinterest? Check out my Flower Gardening board for more ideas. You can also find me on Facebook.

Kelly Martin

Hi, I'm Kelly Martin, a landscape gardener and designer with over 10 years experience. I have a passion for small space gardening and I love designing and creating beautiful outdoor spaces that maximize the potential of small urban gardens. Read more