How to make those hydrangeas explode with color

She offered these tips so you, too, can grow the prettiest hydrangeas on the block:

Know the type

The most widely grown variety is Hydrangea macrophylla, with its big mopheads of blue, pink or white flowers. There are also lace cap varieties where the blooms have an outer ring of large florets and a mass of tiny fertile flowers in the center.

H. arborescens "Annabelle" has big balls of flowers that start green, turn white and then dry a pale green. Their heavy heads of blooms sometimes droop, so Ward likes to cut hers back to about 20 inches in early March and then put in a green tomato cage. Within weeks the plants cover the cage and the wires keep the flowers from flopping.

Oakleaf hydrangeas, H. quercifolia, are our natives and require the least care. They’re the most drought-tolerant. The long pyramid-shaped blooms open white and then fade to pale pink or even burgundy in some varieties.

H. paniculata, commonly referred to as the PeeGee hydrangea, is another variety with big pyramid-shaped clusters of white flowers that literally weigh down the branches. H. serrata varieties have smaller leaves and flowers, and they bloom later into the summer.

Know where to plant and how to prepare the bed

“People think hydrangeas must have shade, but what they really want is morning light and a respite from the broiling afternoon sun,” Ward said. A high canopy of trees is ideal. In full sun, the whole plant will wilt by midafternoon, even if it was just watered that morning.

Hydrangeas need a break from our hard-packed soil. “We can’t plant hydrangeas in our native clay alone,” Ward said. Hydrangeas will do best if the soil is amended with lots of organic matter and something such as granite chips that will break up the clay and promote drainage.

Know when to prune

This confuses people more than almost anything else about hydrangeas. The big leafed hydrangeas, H. macrophylla, bloom on last year’s branches. Whether mophead or lace cap, if you want to prune them, do it right after the blossoms are finished, and definitely not after Aug. 1. That way the plant has time to set new buds for next year.

The other types bloom on new branches, so you can prune them any time up until they form those blooms in the summer.

Ward uses pruning to rejuvenate old hydrangea bushes, removing the old, dead branches, and taking about a third of the healthy canes throughout the bush. “This creates airflow and stimulates new, vigorous growth,” she said.

If you’re cutting the blossoms for cut flowers, Ward suggests thinking of that as pruning and cutting back far enough to help rejuvenate the plant. Then submerge the whole flower head and stem in cool water for several hours. Now the blooms should have a long life in your flower arrangement.

Fertilize at the right time

During drought, you don’t want to stress your plants by fertilizing them and asking them to put out new growth. But now that the rains have come, Ward is back to her regular schedule of fertilizing on April 1 and July 4. She uses a 10-10-10 fertilizer and puts about a cup of fertilizer around the edge of each fully grown shrub. “Hydrangeas have very shallow roots, so it’s important to apply your fertilizer on moist soil, scratch it in and then water it again so you don’t burn those roots,” she said.

While fertilizing, add some aluminum sulfate to help your hydrangeas stay as blue as possible. Ward mixes 20 pounds of Super 10-10-10 fertilizer with 4 pounds of aluminum sulfate and uses that to feed her plants. If you want your flowers more pink, add dolomitic lime several times a year instead of the aluminum sulfate.

American Hydrangea Society 2010 Garden Tour

Six gardens in metro Atlanta

10 a.m.-5 p.m., Saturday, June 12

Tour is open to society members; memberships can be purchased for $25.

For outlets where membership is sold, go to www.americanhydrangeasociety.org.