Hydrangeas are flowering shrubs that are easy to grow and can provide color in the garden from mid-summer through fall. They are used as specimen plants and in shrub borders. The flowers of some species can be dried and used in flower arranging and crafts.
The name comes from the Greek "hydra," meaning "water" and "angeon," meaning "vessel," referring to the plants preference for moisture and to the shape of the seed capsule.
Hydrangeas were first introduced by Sir Joseph Banks from a Chinese garden in 1739. The birth flower of June, they're almost always blooming then.
Bigleaf Hydrangea ( Hydrangea macrophylla ) is the most commonly planted kind, and the one with the largest and most show-stopping blooms.
Bigleaf Hydrangeas prefer partial shade. Morning sun and afternoon shade is perfect in inland areas, while on the coast, no shade is required. Give them moist, well-drained soil. Avoid planting hydrangeas on hot, dry, exposed sites.
Bigleaf hydrangeas form their flower buds in late summer for the following year, so pruning in late summer, fall and winter will remove potential flowers.
Prune bigleaf hydrangeas when the flower heads begin to fade. Prune off the flower heads and snip back other shoots to encourage branching and fullness. For a dwarfing effect, prune hard back to the double buds forming on either side of the stem near the base of the plant.
Hydrangeas are fascinating in that, unlike most other plants, the color of their flowers can change dramatically.
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. The people who have the most control over the color of their hydrangeas are those who grow them in containers. It 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 end of the spectrum)
It is much easier to change a hydrangea from pink to blue than it is from blue to pink. Changing a hydrangea from pink to blue entails adding aluminum to the soil. Changing from blue to pink means subtracting aluminum from the soil or taking it out of reach of the hydrangea.
Old established hydrangeas may also be divided in the early spring, by digging them up and using a shovel to divide the clump, much as you would divide a perennial. This way, several plants can be obtained from one mature clump. Be sure to water the plants in very well, and keep watering all summer.
Here is a great resource for hydrangea information on the Web:
The American Hydrangea Society