Hydrangea Hues

The Hydrangea is a favorite to many gardeners and has become quite popular in the south, since they are hardy, easy to grow, and require little maintenance. Hydrangeas bloom in whites, blues and pinks, and the color depends on the soil conditions. Unlike most other plants, the color of their flowers can change dramatically. To change the color of your hydrangea, you will need to alter the pH of the soil.

To change CHANGE TO PINK

Hydrangeas turn pink because they are deprived of aluminum. This can be accomplished by doing the following:

Add dolomitic lime to raise the soil pH to about 6.0 to 6.5.

Grow your hydrangeas in pots - soil-less potting mixes don’t usually contain aluminum, so there’s no chance of your hydrangea reverting to blue. In a pot, it will be much easier to control the requirements for growing pink hydrangeas.

Fertilizer - choose a high phosphorus fertilizer, since phosphorus seems to prevent hydrangeas from accessing aluminum Choose a fertilizer close to the ratio of 25/10/10 (Phosphorus is the middle number).

To change CHANGE TO BLUE

Hydrangeas turn blue as a reaction to aluminum in the soil. This can be accomplished by doing the following:

Soil pH should be slightly acidic (5.2 - 5.5).

Do a soil test to determine your starting pH. If the soil naturally contains aluminum and is acid (low pH) the color of the hydrangea will turn shades of blue and/or purple.

Add aluminum sulfate to the soil to help lower the pH. A solution of 1/2 oz (1 Tbsp) aluminum sulfate per gallon of water be applied to plants (which are at least 2-3 years old) throughout the growing season. If aluminum is naturally in your soil and the pH is low, your hydrangeas are probably already blue. But even if you have naturally acidic soil, you may need to add some aluminum sulfate.

Important:
Water plants well in advance of application and put solution on cautiously, as too much can burn the roots.

Not all plants can tolerate acidic soil and neighboring plants may be affected. Always follow label recommendations when adding amendments to your soil.

Fertilizer with a high potassium, low phosphorus fertilizer to help maintain your blue color. Choose a fertilizer with an approximate ratio of 25/5/30 is good (potassium is the last number). Superphosphates and bone meal should be avoided when trying to produce blue.
 It is important to have your water tested so that it will not "contaminate" the soil that you have worked so hard to balance. The pH of the water should not be higher than 5.6.

Even if you have hydrangeas that turn pink or blue, adding more amendment to the soil will not intensify the depth of color. Color may vary from season to season due to weather, plant stress and changes in the environment. Plants near a concrete foundation or walkway may never turn blue because of the lime that leaches out of the concrete. And remember, altering your soil to change your hydrangea’s color is not a one time thing. You will have to maintain the altered soil conditions.


{ Happy Gardening! Posted by McDonald Garden Center, June 16, 2010 }