The secret to getting that gorgeous sapphire color is in the soil. Here's how to bring out the blues in your flowers.

By Karen Weir-Jimerson
Updated June 23, 2020
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Almost like a mood ring, you can change the flower color of certain hydrangeas from pink to purple and sky blue. But instead of temperature changing the color as in a mood ring, it's the pH, or the acidity, of the soil your hydrangeas are planted in that controls the hue of the blooms. By adjusting the pH, you can turn pink flowers into blue (or blue flowers into pink). To grow the best blue hydrangeas on the block, it all starts with testing your soil; if it's not acidic enough, you may end up with pink or purple flowers instead. Follow these tips to make sure you'll get gorgeous blue flowers every time.

blue 'Brestenberg' hydrangea flowers
'Brestenberg' is a variety of bigleaf hydrangea that produces huge clusters of blue flowers when planted in acidic soil.
| Credit: Kritsada Panichgul

1. Choose the Right Kind of Hydrangea

Only the flowers of bigleaf hydrangea (Hydrangea macrophylla) can change color. Other types such as oakleaf hydrangeas or smooth hydrangeas such as 'Annabelle' only bloom in white or cream. These plants are just as full and beautiful, but if your goal is blue hydrangeas, make sure you're planting varieties that can turn the shade you want.

blue cluster of endless summer hydrangea
Deadhead Endless Summer hydrangeas when the flowers start to wilt; as long as you do, the plant will keep blooming all season.
| Credit: King Au / Studio Au

2. Choose Blue Varieties

Look for hydrangeas that are bred to be blue such as 'Nikko Blue', Endless Summer The Original, 'Penny Mac', 'Blauer Prinz', or Endless Summer Twist-n-Shout. The photo on the plant tag will help you choose blue-blooming varieties if the plants aren't in flower at the nursery.

3. Measure the Soil pH

Although doing this may sound like complicated chemistry, it's not. All soil has a pH value which measures the acidity or alkalinity. The pH scale is from 0 to 14; 7 is neutral. Soil pH values of less than 7 indicate degrees of acidity. Soil pH values greater than 7 indicate degrees of alkalinity. Use a soil test kit to determine the current pH levels of your soil.

Pink Hydrangea
When soil pH gets closer to neutral, bigleaf hydrangea flowers will look purplish.
| Credit: Alise O'Brien Photography

4. Pick the Flower Hue You Want

For true blue flowers, the hydrangeas need to be grown in acidic soil with a pH of 5.5 or lower. For pink flowers, the plants need neutral to alkaline soils (pH 6.5 and higher). For purple blooms (or a mix of blue and pink flowers on the same plant), the pH of the soil must be between pH 5.5 and 6.5. The results of your soil test will help you figure out what to do next.

5. Adjust the Soil pH

Most garden soils tend to be neutral so you'll need to amp up the acidity to go blue. You can do that in a variety of ways. Organic acidifiers include sulfur and sulfate. There are also easy-to-use soil additives made specifically for hydrangeas. Bailey's Color Me Blue (soil sulfur) or Bailey's Color Me Pink (garden lime) change the pH of the soil so you can enjoy the hydrangea bloom color you want. These all-natural products make the soil more acidic (for blue blooms) or alkaline (for pink blooms). Add the pelleted mixture to the soil when you plant your hydrangea.

6. Continue to Acidify the pH for Blue Blooms

Your soil pH likely will need regular adjustment to produce consistently blue blooms. Gently work acidifying soil additives into the top layer of the soil around the root zone whenever you'd normally fertilize your hydrangeas, usually in early spring. Also, if you're starting with alkaline or neutral soil and trying to make it more acidic, remember that your hydrangeas won't suddenly turn blue overnight. It'll probably take multiple applications to make your soil acidic enough, and if your hydrangeas have already bloomed pink, you might not see blue flowers until next year.

Comments (2)

Anonymous
April 1, 2020
Great article. I've always heard you can add coffee grounds to the soil to get blue flowers. Has anyone ever tried this with any success?
Anonymous
April 1, 2020
Great article. I've always heard you can add coffee grounds to the soil to get blue flowers. Has anyone ever tried this with any success?