Here’s How to Change the Color of Your Hydrangeas
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If your hydrangea blooms are pink instead of blue—or vice versa—there's a way to get the color you want. Here's how to change hydrangea color for the perfect hue.
The plant tags on your ‘Endless Summer’ hydrangeas promised beautiful sky-blue flowers—so why are the blooms completely pink? For how to change hydrangea color, take a closer look at the dirt they’re growing in.
Here’s the Secret…
It’s in the soil! The key to color-changing hydrangeas is whether the soil is acidic (low pH) or alkaline (high pH.) In order for hydrangeas to be a beautiful blue, the soil must be on the acidic side, with a pH lower than six. You can test this with a soil pH meter like this one. You can also look at your hydrangea blooms: If they’re pink, then the soil is alkaline.
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Which Hydrangeas Change Color?
Before you think about changing your soil, know that not all hydrangeas change color. Hydrangeas with white or ivory blooms like oakleaf, ‘PeeGee’ or ‘Annabelle’ types aren’t affected by the pH of the soil. These hydrangea flowers will stay white, though a few cultivars like ‘Vanilla Strawberry’ may blush from white to pink.
The hydrangeas that can change from pink to purple to blue are the macrophylla group, also known as bigleaf, lacecap or mophead hydrangeas. (Lacecaps have flat blooms with frilly edges; mopheads have large, globe-shaped flower heads.) Varieties of this group include ‘Endless Summer,’ ‘Nikko Blue,’ ‘Summer Crush,’ and ‘L.A. Dreamin.’ Though some of these varieties have “blue” or “red” in their names, all bigleaf hydrangeas can change color.
How to Get Blue Hydrangeas
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To turn your hydrangea flowers blue, lower the soil pH to 6.0 or lower. You can do this by purchasing a soil acidifier plant fertilizer to feed your hydrangeas every one to two weeks. Or, lower the pH of the soil organically by spreading pine needle or pine bark mulch around the plants. Coffee grounds can also help make soil more acidic, as well as compost tea, vinegar or peat moss added to the soil.
A lack of aluminum in the soil can also prevent hydrangeas from turning blue. Because excess aluminum can be toxic to plants, confirm aluminum levels with a soil test before buying additives.
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How to Get Pink Hydrangeas
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Pink hydrangea blooms need alkaline soil, with a pH of 7.0 or higher. To make the soil more alkaline, you can work in ground or powdered limestone or wood ash. You will need to do this several times during the growing season. Keep in mind that it is more difficult to make soil more alkaline, so it will likely take longer than the process for blue flowers.
How to Get Purple Hydrangeas
Hydrangea flowers will turn shades of reddish-purple to pale purple when the soil pH is somewhere in between acidic and alkaline. You will often have purple flowers during the process of raising or lowering the soil pH. To achieve purple shades, aim for a pH between 6.0 and 6.9.
Be Patient with Your Garden
Changing the pH of your soil will take some time, so know that these color changes won’t happen overnight. It will take several weeks or even months of amending the soil, as well as taking these steps in subsequent seasons.
If you’re hoping to see hydrangea color change happen more quickly, try planting a small hydrangea in a container. You’ll be able to change and control the pH in potted soil much more easily, and this is a fun way to experiment with hydrangea color. Here are even more ideas for taking your garden from good to great!