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How to change hydrangea color

To change a hydrangea’s flower color, start by testing and then adjusting the soil pH. For blue flowers, use sulfur to reduce the pH down to 5.5 or lower. For pink flowers, use limestone to bring the pH up to 6.5 or higher. Controlling soil aluminum and minor nutrients can also help with changing bloom tones.

Hydrangea macrophylla - pink to blue

How to change hydrangea color

Hydrangeas are one of the most sought-after flowering shrubs in the garden. These beautiful plants are usually a reliable way to add texture and color to the garden. But what if the blooms are not the color you imagined?

The flowers of certain types of hydrangeas – namely Hydrangea macrophylla and Hydrangea serrata, are most commonly changed by adjusting soil pH. In general, making soil more acidic will lead to bluer flowers, while bringing up the alkalinity will lead to pinker flowers. Changing the color of the flowers can take several weeks, months, or years, depending upon your soil conditions and desired color.

Hydrangea macrophylla - different colors - pink, purple, blue

Types of hydrangeas that can change flower color

First, whether or not you can change the color depends upon the species of hydrangea you are growing. You can use soil amendments to change the flower color of bigleaf hydrangeas (like Endless Summer, Bloomstruck, and Summer Crush) and mountain hydrangeas (like Tuff Stuff). But for other species of hydrangea like panicle, oakleaf, or smooth, changing the pH of the soil will not change the color of the flowers.

Soil pH and hydrangea soil

The ideal natural soil pH for many hydrangeas is in the 5.5-6.5 range. This is slightly acidic. Within this ideal pH range, the flowers tend to be purple in color.

While purple is certainly a lovely color, many gardeners want to encourage their hydrangeas to turn either blue or pink. For really blue flowers, the pH should typically be at or below 5.0 (even though this is not strictly ideal for the plant’s overall health and nutrition). For deep pink flowers, the pH should typically be approaching 7.0 (neutral).

Blue hydrangea flowers on low shrubs
Blue flowers require strongly acidic soil and adequate available aluminum

How to turn hydrangea flowers blue

To turn hydrangea flowers blue, gardeners can try adding sulfur to their soil. Sulfur is an excellent soil acidifier and will help reduce your soil’s pH. Some soil acidifier products also contain gypsum.

The lower the pH, the bluer the flowers will be. Typically, a soil pH of about 5.0 is a good target for blue hydrangeas. You may also want to add some aluminum sulfate to increase the blue effect.

Gardeners should add sulfur or soil acidifiers (usually sulfur and gypsum) in small amounts and gradually test how much they need to get the desired color. Most of the time, this means adding a small amount regularly (especially during the active growing season) and then testing how low you can bring the pH level before your plants start to suffer. Bringing soil pH below 5.0 is not recommended, as important nutrients like nitrogen, phosphorus, and potassium become quite limited in strongly acidic soil.

Pink hydrangea macrophylla with blue blossoms behind
Pink hydrangea flowers require neutral to slightly alkaline soil without too much excess aluminum

How to turn hydrangea flowers pink

To turn hydrangea flowers pink, gardeners can use lime (dolomite limestone). Garden lime is a great way to raise soil pH and will help make your hydrangea flowers pink. A neutral soil pH of around 7.0 seems to be a good target for pink blooms.

To get the best results, gardeners should add small amounts of garden lime/limestone regularly (especially during the active growing season) and then test how high you can raise the pH with your soil amendments before your plants start to suffer. Bringing soil pH too high is not recommended, as some essential nutrients like iron and manganese become unavailable to the plant in alkaline soils.

Soil pH adjustment for hydrangea flower color effects

The most common way to change hydrangea flower color is to adjust the soil pH. By adding small amounts of either sulfur or garden lime regularly, you can slowly change the pH of your soil to get your desired bloom color. Just remember not to push too far in either direction, as both acidic and alkaline soils can have adverse effects on your plant’s health.

Start by getting a soil test to determine soil pH. If you already have growing hydrangea plants, note the color of their blooms. It is especially helpful if you have photos of the plant from several previous seasons.

Here is a guide for soil pH levels in relation to estimated hydrangea flower color:

Blue flowers: pH of 4.5 – 5.5 (certain nutrient availability is low below about 5.0 pH)

Purple flowers: pH of 5.5 – 6.5 (ideal for the health of the plant)

Pink flowers: pH of 6.5-7.5 (certain nutrient availability is low above about 7.5 pH)

These numbers are just a guide. Flower color is also affected by other environmental conditions, including major nutrients like phosphorus and minor nutrients like aluminum.

Controlling aluminum for flower color-changing effects

Aluminum in the soil is another important factor in the color of hydrangea flowers. In nurseries, aluminum is either added or withheld to affect the color of the flowers.

Increasing soil aluminum content by adding aluminum sulfate is a common way to change hydrangea color bluer. For a truly blue hydrangea plant, try bringing the pH down to around 5.0 by adding aluminum sulfate. Also, be sure not to add too much phosphorus, as high phosphorus levels can prevent aluminum uptake by the plant since phosphorus can react with aluminum in acidic soils.

Decreasing aluminum availability by adding lime is a great way to make hydrangea flowers pinker. Lime helps reduce how much aluminum the plants can absorb, leading to rosier blooms.

By following this guide, gardeners can learn how to manipulate soil pH and aluminum levels to get the desired hydrangea flower color. With a little bit of experimentation and testing, you should be able to get the color of your hydrangeas just how you want.

Mary Jane Duford
Mary Jane Duford

Mary Jane Duford is a quintessential Canadian gardener. An engineer by trade, she tends to an ever-expanding collection of plants. In her world, laughter blooms as freely as her flowers, and every plant is raised with a dash of Canadian grit.

Mary Jane is a certified Master Gardener and also holds a Permaculture Design Certificate. She's also a proud mom of three, teaching her little sprouts the crucial difference between a garden friend and foe.

When she's not playing in the dirt, Mary Jane revels in her love for Taylor Swift, Gilmore Girls, ice hockey, and the surprisingly soothing sounds of bluegrass covers of classic hip-hop songs. She invites you to join her garden party, a place where you can share in the joy of growing and where every day is a new opportunity to find the perfect spot for yet another plant.

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