Changing The Color of Hydrangeas

Changing The Color of Hydrangeas

You say you want your hydrangeas to be in the pink or feeling blue? Success depends on what type of hydrangea you have and the pH of your soil.

Some hydrangeas will never change color. A white ‘Annabelle’ will always have white fading to green flowers. Limelight will always be green that turns white and then pink, and varieties of Hydrangea paniculata, such as the old fashioned Pee Gee, ‘Tardiva’ and ‘Little Lamb’ will produce white flowers that age to pink. There is no way to make these varieties turn blue.

Most mop heads (H. macrophylla) and lace caps (H. serrata or H. macrophylla normalis) hydrangeas can be made blue or pink. Depending on how acidic or alkaline your soil is, this color change can be easy or require a bit of time and effort.

It’s the aluminum in the soil that turns hydrangeas blue, but the plant only absorbs this element in acidic soils. So if you want blue hydrangeas you need to have acidic soil. In some parts of the country the ground is either naturally acidic or is constantly kept that way due to acid rain. This is why hydrangeas are blue on Cape Cod if the gardener does absolutely nothing.

On Cape Cod we don't have to work hard to keep hydrangeas blue... unless the pH of the soil is being raised by the irrigation (town water), lime from the lawn, or nearby concrete.

If the native conditions favor alkaline soil, and you want your hydrangeas to be blue, you’ll need to apply an amendment around your plants that will turn that soil acidic. The most common product sold for this purpose is aluminum sulfate, but sulfur can be used as well. No matter which you choose, be sure to apply the product according to directions. Too much can harm your plants.

When your soil is acidic and you want your hydrangeas to be pink, you’ll need to spread lime and/or wood ashes around your plants. In some areas it might be necessary to apply a good amount of lime twice a year in order to keep the soil alkaline.

In either case, the change in flower color won’t be instant. If your flowers are already blue you might have to wait until the next summer to see pink petals appear.

Many mop-head hydrangeas start out white or green before turning pink or blue. This is natural and doesn't mean that you need to add anything to the soil...just sit back and enjoy the show!

Can you have a Hydrangea with some blue and some pink flowers? Absolutely. Just divide the area around your shrubs into quarters, and amend the soil on two opposite sections to create alkaline conditions and on the other two areas to make the dirt acidic. Be sure to note which area is which so you don’t end up switching and canceling out the blue or pink effects.

Finally, some amount of the color you see on a hydrangea is due to genetics. A ‘Nikko Blue’ Hydrangea will always be light blue or light pink, never dark purple. In most cases you can change the color but not the intensity of that hue.

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