It may be the heat - the cooler the temperatures, the more vivid the flower color.

Hydrangeas are fascinating in that, unlike most other plants, the color of their flowers can change dramatically. Hydrangeas will change hue and intensity of color depending on the degree of acidity or alkalinity of the soil. Simply put, acidic soil produces or deepens blue colors while alkaline soil turns the flowers mauve or pink.

It would be nice if one could change the color of hydrangeas as easily as it changes in this little picture. But it is not easy. Typically, t is much easier to control or alter the pH of the soil in a container than it is in the ground.

On the other hand, hydrangeas often change color on their own when they are planted or transplanted. They are adjusting to the new environment. It is not unusual to see several different colors on one shrub the next year after planting. (They invariably shift toward the red/pink end of the spectrum)

If you live in a hot climate, like we do, it is unlikely you will ever see a "true red" hydrangea. No matter how convincing those pictures in the catalogs are or how much lime is added to the soil, one can only achieve a very deep or dark pink, but not a true red.

One can rarely change the intensity of a color (how strong or pale the color is). The intensity develops for a number of reasons: the heredity of a particular hydrangea variety, weather conditions (hot or cold, humid or dry), health of the plant, and possibly other natural factors. Fertilizing hydrangeas once or twice a year may result in a little more saturated color simply because the health of the plant may be improved.

A few varieties of hydrangeas tend more toward the pink or the blue range of colors, but will not retain even this color if soil conditions are not right.

To promote stronger blues in neutral to slightly alkaline soils, apply one-half pound of sulfur per square yard: if the pH or your soil is 7.75 or higher, however, you may have to resign yourself to pink blooms. If you're a regular coffee drinker, try dumping your daily used grinds around the plants.