Pink, or Blue?
We aren’t talking about babies although wouldn’t it be interesting to be able to control whether or not you had a boy or a girl simply by changing one thing that you eat? Hydrangea plants have the ability to change their color to vary between shades of pink and blue depending on the pH of the soil they reside in. Specifically, it’s the Hydrangea macrophylla or serrata species that have this unique ability.
Change your soil pH
How can you help a hydrangea change its color? The pH and the presence of aluminum in the soil the plant lives in has everything to do with what color the flowers will blossom. Hydrangeas that bloom in shades of pink are plants that are not subject to aluminum and who’s soil has a pH of 6.0 to 6.2. To bloom blue, a hydrangea needs aluminum to lower the pH of the soil to about 5.2 to 5.5. Sounds simple, doesn’t it? Unless your business depends on it, it’s not worth getting upset about the color of your hydrangea bush because, on some level, it can be a difficult thing to control.
Before you can adjust the pH of your soil, you’ll need to know your starting pH point. An inexpensive soil test kit can help you determine the pH or you can take soil to a local garden center and have it tested professionally.
A hint of lime!
For a pink hydrangea, there are a few things you can try. It’s imperative that the plant not be exposed to aluminum. The best way to keep aluminum at bay is:
1) Raise the pH of the soil by adding dolomitic lime several times a year. Espoma has an excellent product that is safer than hydrated lime called Garden Lime. It’s pelletized for easy application and comes in 6.75lb bags.
2) When buying fertilizer, look for one with a ratio of 25-10-10. The middle number is the amount of phosphorus and to help the plant to bloom pink, you’ll want to increase the amount of phosphorus present in the soil. Phosphorus helps to prevent aluminum from invading the plant.
3) If you notice mostly blue hydrangeas in your area and you really want yours to be pink, consider keeping your hydrangea in a container. This allows you to have more control over the pH level of the plant.
A blue hydrangea can be an easier result to achieve as instead of trying to prevent aluminum from reaching the plant, you want to encourage the presence of aluminum.
2) Adding organic matter like coffee grounds or grass clippings also helps to lower the pH of the soil.
3) As with turning a hydrangea pink, it increases your chances of achieving your desired bloom color by keeping the plant in a container.
Once White, Always White
Under no circumstance whatsoever will you be able to change a white hydrangea to pink or blue. White hydrangeas will always be white no matter what you add or subtract to its soil. Another factor to consider is that many plants will change their color on their own when first planted or transplanted. Perhaps you received a beautiful, pink hydrangea as a gift but when you planted it, it changed to a blue hue. Even under the best of circumstances and valiant efforts, the plant needs to adjust to its new environment and that may mean a couple of years of color uncertainty.
Hydrangeas are a beautiful addition to any landscape and regardless of color, have stunning and plentiful blooms. They are easy to grow and with proper care and pruning, your hydrangea will provide you with a long lasting color display throughout the summer months.
For more information about the proper care and fertilizing of your hydrangea plant, we have two downloadable fact sheets available: Hydrangeas: Color and Fertilizing and Hydrangeas: Pruning for Blooms.