Hydrangeas

Hydrangeas give you so many choices for brilliant color when the days grow long and hot.

Marty Wingate November 26, 2010

When you think of hydrangeas, low-growing shrubs with big, dusky blue flower clusters usually come to mind. But the hydrangea family includes a diverse selection of options for your landscape, including an elegant climbing vine and a stately native shrub with large, oak-leaf-shaped foliage. These versatile plants rarely suffer from pest and disease problems, and they grow in a wide range of zones, which explains why they make themselves at home in organic gardens from Maine to Oregon.

Familiar, but Better
The bigleaf hydrangea (Hydrangea macrophylla), also known as the French hydrangea, is the most familiar. This species encompasses two groups, distinguished by the type of flower they produce: the mopheads, also known as hortensias (H. macrophylla var. macrophylla), and the lacecaps (H. macrophylla var. normalis). Both types are hardy in USDA Plant Hardiness Zones 6 through 9 and grow from 3 to 5 feet tall and wide.

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The well-known flowers of H. macrophylla turn pink or blue depending on the pH of your soil. Choose an uncommon variety, however, and you'll have more than the flower's color to admire. 'Nigra' (a mophead type) features black stems that set off the plant's green foliage long before any flowers appear. And 'Lady in Red', a lacecap that's new for 2005, flushes burgundy in the fall, but its red stems and red-veined leaves make it appealing all season long.

6 Exceptional Choices
'Bluebird' (H. serrata) balances delicate lacecap flowers atop a small shrub that only reaches 3 feet.

'Alice' (H. quercifolia) adds drama to large shady areas with its supersized oak shaped leaves and delicate flowers.

'Nigra' (H. macrophylla) sets off large blooms with striking black stems that pop out of the landscape in winter.

'Limelight' (H. paniculata) illuminates the garden for months in the summer with its unusual pale green blooms. Choose this extremely hardy shrub to fill in a large, sunny section of your yard.

'Endless Summer' (H. macrophylla) blooms for a long period and in very cold zones, making it the perfect choice for Northern gardeners.

The climbing hydrangea (H. anomala subsp. petiolaris) adds a surprise element with lacy blooms that cover the vigorous vines. For gardeners who want the unexpected.

Extreme Zones
Bigleaf hydrangeas (H. macrophylla) need special attention in the hottest and coldest zones. In the hot climates of the Southeast and Southwest, plant them in a shady spot or where they get only morning sun. And make sure they get consistent moisture, advises the New Mexico State University Extension Service. Extreme heat can make even shade-grown shrubs wilt, but watering revives them.

In cold areas, you must prevent bigleaf hydrangea stems from freezing to the ground, or they may not survive winter. Surround the shrubs with chicken wire, fill the center all around the stems with dried leaves, and cover the cage with burlap. Even with these measures, growing hydrangeas in cold, dry areas such as the Rocky Mountain states is risky, because of the region's drought problems and water restrictions.

H. serrata is much like H. macrophylla, except that it grows into a smaller, more compact shrub. University of Maine Cooperative Extension Specialist Lois Berg Stack notes that in Zones 3a through 5b, H. serrata seems more hardy than H. macrophylla, although neither will survive reliably in climates colder than Zone 5.

Native Beauty
The beautiful oakleaf hydrangea (H. quercifolia, Zones 5?9) is native to shady stream banks in eastern North America. Most varieties grow 4 to 6 feet tall and wide, with white flowers, and leaves that are indeed shaped like those of an oak, only larger. The leaves begin the year with a rusty look and continue to have a roughness to them throughout the summer. In fall, the foliage turns varying shades of burgundy.

One of this shrub's finer points is that it suckers (sends up vigorous shoots from its roots) slightly, which makes it easy to divide if you want more plants. You can choose from several varieties, including the astoundingly large 'Alice', which grows to 12 feet tall and wide with 12-inch panicles—highly branched flower structures—to match. On the other end of the spectrum is 'Pee Wee,' which tops out at about 3 feet.

In moist, temperate climates, such as the Pacific Northwest, the oakleaf hydrangea grows beautifully as a dry shade plant, but in hotter climates or if sited in more sun, it needs consistent moisture. It is a robust grower in morning sun, reports Ed Gilman, Ph.D., professor of horticulture at the University of Florida, who has an 8-foot-tall, 12-foot-wide specimen in his own garden. In very cold climates, protect the stems of oakleaf hydrangeas from freezing in the same manner you would bigleaf types.

A Fine Vine
The climbing hydrangea (H. anomala subsp. petiolaris, Zones 4-9) is a fabulous choice where you want to cover a large tree trunk or decorate a wall. The vine, left unpruned, can reach up to 50 feet or more. Its aerial roots cling to craggy surfaces such as the furrows in the bark of a tree. Grown freestanding, it becomes a hulking, shrublike form. White lacecap blooms garnish the plant in summer.

The climbing hydrangea also works well trained against a wall; or, to make the background surface easier to repaint, you can provide the plant with a sturdy trellis. As an espalier, the climbing hydrangea adds a formal dimension to your garden, and the structure of its winter branches—in addition to its exfoliating bark—offers as much ornament out of flower as in. I've seen a climbing hydrangea growing happily in the Pacific Northwest on a wall 8 feet long and 6 feet high for more than 10 years. The climbing hydrangea also fares well in Maine, especially along the coast, reports the University of Maine's Lois Berg Stack.

Cold-Ready
In the coldest climates (which includes Zones 3a through 5b), grow the hardiest of hydrangeas, H. arborescens and H. paniculata, says Stack. The oakleaf and bigleaf types are generally too tender to survive frigid winters.

H. arborescens blooms on new growth—wood that develops in spring. This makes it an easy choice in cold climates because blooms aren't formed on old wood—wood that developed the previous year—which may die back during the winter. Gardeners that prefer not to worry about when and how much to prune also find this shrub easy to care for. H. arborescens can be cut back in late winter to early spring (before new growth begins) and still produce lovely white flower clusters in summer. The cultivar 'Annabelle' bears immense heads of sterile flowers.

If you really love the bigleaf types but you live where winters are rough, a new introduction may be just what you are looking for. 'Endless Summer' has survived winter in Minnesota and come back to bloom in vivid pink the following season. A combination of traits makes this plant a winner in the north. Unlike most bigleaf hydrangeas, it blooms on both old wood and new, and it survives Zone 4 winters. "People are quite excited about 'Endless Summer'," says Stack.

Of course, no matter where you live, it's easy to get excited about hydrangeas, because they require so little from us and give back so much!

Pruning for Blooming
No blooms on your bigleaf hydrangea this year? Improper pruning may be the cause. But never fear: Pruning a hydrangea the right way is easy if you follow these guidelines.

Keep some of this year's growth. Gardeners often inadvertently cut off next year's flowers because Hydrangea macrophylla flower buds tend to form at the tips of branches and on old wood, meaning that the buds for next year's blooms form on this season's growth.

Remove one-third of the shrub's stems. Each year, keep the shrub less dense and rejuvenate it by removing up to one-third of the stems as close to the ground as you can, beginning with the oldest growth. Do this after the shrub has finished blooming; the remaining stems will bloom with bigger flowers than you had before when the shrub was crowded with branches.

Prune after bloom. Remove old flowers by cutting to just above the swollen buds for next year. And remember to cut off only the dried flower head, no further down.