‘Endless Summer’, ‘Annabelle’, ‘Tardiva’ — the names roll easily off my tongue, calling to mind the refreshing beauty of the summer-flowering hydrangea. Given proper care and placement, hydrangeas begin their show in June and continue well into late summer. And as the number of varieties, the bloom size and the range of colors continues to grow, so does the passion gardeners have for this group of plants.
The generally coarse summer foliage fits nicely into the border alongside finer-textured perennials. And if cut and dried before they fade, the flowers will last well beyond the growing season, working nicely into floral arrangements. Meanwhile, the peeling bark on the stems and the spent blooms remaining on the shrubs will enhance the winter landscape.
Native to the Southern Appalachian woodlands as well as Asia, hydrangeas can be placed in just about every landscape niche, depending on the selection.
The bigleaf hydrangeas are divided into two groups — the hortensias (or mopheads) and the lacecaps. Between them, they contain more than 500 cultivars. Mopheads are so called because of their large, round form. But these showy flowers (or inflorescences) are actually made up of hundreds of smaller, sterile blossoms that, en masse, can grow so large the stems will bend and break beneath their weight.
Until recently, you wouldn’t find this plant flowering much north of here unless it was well sited, protected and properly cared for. But a recent study by our esteemed (and now retired) friend Dick Bir of the Mountain Horticultural Crops Research and Extension Center found a number of mophead hydrangeas that are hardy to zones 5-9, including the following blue, violet and pink selections: ‘All Summer Beauty’, ‘Nikko Blue’, ‘Mathilda Gutges’ and ‘Glowing Embers’. Of course, ‘Endless Summer’ has been all the rage lately, because it flowers on new wood (i.e. stems less than about nine months old) and blooms repeatedly throughout the summer. The lacecaps can have various combinations of both sterile and fertile flowers, providing unusual but deliciously delicate displays. Dick’s research on lacecaps found that ‘Bluebird’, ‘Tokyo Delight’ and ‘Coerulea’ (among others) are beautiful and hardy to this area.
The bigleaf’s flowers bloom on the old wood, making them vulnerable to winter dieback as well as early-fall and late-spring frosts. North- and east-facing slopes are the best planting sites, since they’re less susceptible to midwinter temperature fluctuations. An evergreen canopy can also help protect against frost.
Hydrangeas that seem reluctant to flower may reflect improper pruning, too much (or too little) water, high-nitrogen soil or perhaps excessive shade. It isn’t really necessary to prune hydrangeas except to remove deadwood and spent flowers or to do minor shaping. But any heavy pruning or cutting back of healthy growth should be done immediately after the shrub has finished flowering, because pruning in the spring, fall or winter will also remove flower buds. For the most part, the soil pH steers the color from pink to blue. A higher pH (more alkaline) will gift you with shades of pink; more acidic soils (lower pH) will bring forth the blues. Some varieties with a more stable color aren’t swayed by the soil pH (or, more accurately, the free aluminum in the soil, which ultimately produces the blue coloration).
When people ask about my favorite shrub, I always think of oakleaf hydrangea, in part because there’s one that shares my name (‘Alison’). But this native beauty boasts many charms: It’s very cold-hardy; has handsome, peeling bark; provides nice fall color; and features fragrant, long-lasting blooms. And though it does best in moist soils and partial shade and will begin showing fall coloration in late summer under stressful growing conditions, it’s pretty tough and adaptable to most urban settings. It also blooms on new wood, so pruning and winter or frost damage won’t affect its flowering.
The straight species is nice, but the cultivars ‘Snow Queen’, ‘Alice’ and ‘Snowflake’ are certainly splashier. The first two hold their elongated flowers upright, whereas the heavy-headed ‘Snowflake’ will cause the branches to bend over. ‘Alison’ was discovered at the same time as ‘Alice’, though it hasn’t been as heavily promoted. But with its upright flowers and burgundy-red fall color, it’s equally outstanding. That’s OK; my feelings aren’t hurt. And folks will find out soon enough what they’ve been missing all these years! ‘Pee Wee’ and ‘Sikes Dwarf’ are two compact forms that reach a height of 2-4 feet; the larger forms can grow up to 12 feet or so. The oakleaf hydrangea’s elongated flowers can range from 4-5 inches up to 10-15 inches.
Some hydrangea growers emphasize flower size — the bigger the blossoms, the better the plant. But you can never fully understand the “bigheaded” concept until you’ve met ‘Annabelle’. This cultivar of the native smooth hydrangea is similar to ‘Grandiflora'; its large, round inflorescences (6-8 inches across) can become so full and heavy that they hang down, nodding in agreement that it’s time to hit the shade, lie in the hammock and drink iced tea. I consider these the loud, outspoken children whose quieter, more thoughtful parent is found in rocky woodlands from New York to Louisiana. The straight species, best suited to shade and moist soils, can become rough-looking if exposed to too much sun or heat. In colder climates, it’s often treated as an herbaceous shrub, but cutting back the smooth hydrangea does not affect flowering performance. In fact, rumor has it that pruning this plant right after it flowers can bring on a second flush of blooms in the same season. “White Dome’ is a new, large-flowering form that’s noted for its cold-hardiness and ability to withstand summer heat.
The panicle hydrangea’s many desirable qualities — urban tolerance, winter hardiness and ability to bloom on new wood — have contributed to its widespread use. The cultivar ‘Grandiflora’ (better known as the PeeGee hydrangea) is probably the most familiar one. Its white, late-summer flowers are more pyramidal in shape but also tend to flop. Recently several new forms have come onto the market: ‘Unique’, ‘Tardiva’ and ‘Pink Diamond’, all offering clean foliage and upright blooms that range from white to pink. ‘Limelight’ is a bright, lime-green flowering form that’s cold-hardy and a strong grower.
Last but decidedly not least is the climbing hydrangea. If left alone, this impressive vine can reach a height of 80 feet or more. It is slow to establish, but planting on a north or east wall can help it along. Picture white flowers, 6-10 inches in diameter, climbing up a wall or stone chimney, with woody stems that lend depth and structure to the wall itself. (Be sure to give this woody vine substantial support.) The glossy, dark-green foliage, fall color and cinnamon-colored, peeling bark help make this one of the best four-season vines for the landscape.
I couldn’t hope to tell the hydrangeas’ whole story — including the incredible contributions they make to the summer garden — in these few paragraphs. But if you’re seeking the unique, the tough, the delightful, this plant group is definitely one to explore.
Elizabeth Dean of Wilkerson Mills Gardens (near Atlanta) will be coming to The North Carolina Arboretum on the evening of Monday, Aug. 23 to teach us more about hydrangeas. For information on her program, check the Arboretum Web site (www.ncarboretum.org) or call 665-2492. In the meantime, a visit to this sweet, family-owned nursery’s own Web site (www.hydrangea.com) will open your eyes to the wonderful world of hydrangeas. And don’t fail to take note of the lovely verse and prose sprinkled throughout the site, which helps remind us to take time on these warm summer evenings to stop life and muse — feet up, cold drink in hand, and eyes feasting on the cool, subtle colors of lacecaps and mopheads.
[Alison Arnold is director of horticulture at The North Carolina Arboretum. She can be reached at: firstname.lastname@example.org.]