Controlling the color of hydrangea blooms in your garden this summer

Published on Wed, Jun 27, 2012 by Kathy Anderson

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Many people grow hydrangeas to enjoy the long-lasting flowers in their landscape. As an added bonus, the blooms of these lovely plants can be easily dried for year-round enjoyment, and unlike most other plants, the color of some hydrangea blossoms can be controlled or changed by gardeners. This is accomplished by regulating the acidity of the soil in which the hydrangeas are planted.

Not all hydrangea varieties can change color. Those that are naturally white will remain white no matter what the soil type they’re grown in. Most hydrangea blooms tend to subtly change color as they mature, but gardeners can only manipulate the colors of those that are naturally blue or pink. This would include the colored Big Leaf and Pee Gee varieties. Big Leaf hydrangeas are also known as mopheads or lacecaps.

If your hydrangea has blue blooms, amending the soil to make it more alkaline will change the blooms to pink. Likewise, a pink hydrangea may be changed to blue by increasing the acidity of the soil. It is much easier to change a pink hydrangea to blue than it is to change one from its natural blue color to pink. And it’s much easier to control the color of hydrangeas that are grown in pots than if they’re grown in the ground.

The presence of aluminum in the soil will make a hydrangea bloom blue. Garden centers carry aluminum sulfate that can be added to the soil around hydrangeas to make the soil more acidic and help them develop a blue color. Be careful when using aluminum sulfate, as too much can burn the roots and harm the plant. Apply it around plants that are at least two years old, and water the plants well before applying this soil amendment. One tablespoon of aluminum sulfate per gallon of water is recommended and may be applied throughout the growing season to retain the blue blooms.

If the soil is naturally acidic with a low pH, the color of the hydrangeas will naturally tend to be shades of blue or purple, and sometimes both colors simultaneously. If you have acidic soil but would rather have pink hydrangea blossoms, the plants must not be given the opportunity to use the aluminum in the soil. The pH needs to be raised to between 6.0 and 6.2, but be careful to not raise it above 6.4. If the pH is that high, the plant will not be able to take up iron and will suffer. A fertilizer high in phosphorus will also prevent the plant from taking up aluminum from the soil.

Hydrangeas planted near concrete sidewalks or a concrete foundation are more likely to produce pink blossoms. Lime can leach out of the concrete and keep the soil pH too high to produce blue blooms. If you absolutely must have blue hydrangeas near a concreted area, it’s best to grow them in pots.

Hydrangeas make excellent cut flowers and the dried blooms make beautiful arrangements. The key to successfully drying hydrangeas is to cut them at the right time.

Unfortunately, it’s difficult to dry hydrangea blooms that have been cut at their peak of color. For best results, allow the blossoms to dry somewhat on the plant before cutting them.

Even the white hydrangeas will turn colors as they age, and most commonly they will turn slightly green, but may also turn light pink or even burgundy. The best time to harvest the blooms for drying is after they begin to change color and dry a bit in late summer to early fall.

After collecting the blooms, they can be placed in a dry, airy room out of direct sunlight until fully dried.

They may be left standing in a dry vase or hung upside down. Either method works well. The method used to dry them isn’t nearly as important as the timing for gathering the blooms.

 



Kathy Anderson has been an avid gardener for many years and has grown tomatoes by the acre, along with many other vegetables, flowers and landscape plants. Anderson recommends freeplants.com as a great place to learn more about gardening.