How to Change Hydrangea Color

Did you know you can change the color of your blue or pink big leaf hydrangea? The color of the H. macrophylla species won't change overnight and won't be absolutely predictable, but you can have a certain amount of control over the bloom color with a bit of chemistry. Learn how.

Controlling Hydrangea Color in Container Pots

Container pot gardening gives you a lot more control over your hydrangea color, because you can better control soil pH levels in pots than in open soil. But should you decide to transplant a hydrangea--even from one side of your yard to the other--you might see a color change. Your hydrangea may take on a new color depending upon its location. In fact, that one large hydrangea plant may even produce a variety of bloom colors on a single plant the following year.

Changing Hydrangea Color from Pink to Blue

The way you change hydrangea color from pink to blue is with the addition of aluminum sulfate (or even aluminum nails) to the soil in which your plant grows. Since it's easier to add a chemical to soil than to subtract it, it's far easier to change hydrangea color from pink to blue, than the other way around.

Color intensity depends upon a number of conditions: hydrangea variety, fertilizer used--as it relates to plant health, and growing zone or climate.

When aluminum is in the soil or is added to the soil at the base of the hydrangea plant, soil pH lowers and hydrangea blooms tend to be blue or purple shades. Also, if fertilizer used is high in potassium but low in phosphorus, you'll get a blue color. For blue color, shoot for a soil pH level of 5.2-5.5.

In a container pot using compost, you can lower the pH easily, but check the pH of your water before you water the hydrangea. If your water has a high pH, you'll not see the nice blues you are hoping for.

Also, did you know that planting your hydrangea too near concrete may raise the pH of the soil and keep your hydrangea colors in the pinks?

Changing Hydrangea Color from Blue to Pink

To change hydrangea color from blue to pink, you need to add lime to your soil. Raise the pH level to about 6.0-6.5 to keep aluminum from being taken up into the plant. For creams, keep soil pH neutral.

Hydrangeas are a spectacular plant with gorgeous blooms. You can control the bloom color of big leaf hydrangeas by controlling the soil pH. Adding aluminum turns blooms blue. Adding lime turns blooms pink. Just remember, to maintain the color change, you'll need to maintain the soil conditions.

Reference:
Marie Iannotti, "Changing the Color of Your Hydrangeas", About.com: Gardening
Changing the Color of Your Hydrangeas