By Charles Kidder
Sometimes I just can’t resist the goofy alliteration that most gardening magazines stoop to for their cover teases. Perhaps I could try “Heavenly Hydrangeas.” But, enough already. Let’s just talk about the plant.
Hydrangeas conveniently go by the same name in both common usage and scientific terms. The only difficulty arises when it comes to pronunciation: some pronounce the first “a” as in ape; others as in annual. I am not too sure which is correct, so take your pick. Either way, several dozen hydrangea species are native to North and South America, as well as eastern Asia, where the greatest diversity occurs. They have long been garden standbys, and breeders are now working on new varieties.
Probably when most people think “hydrangea,” they conjure up Hydrangea macrophylla, a small-to-medium-sized shrub with big blousy pink or blue flowers. (Hydrangea serrata is closely related and is often considered to be merely a variety of macrophylla, with more elongate, less shiny leaves.) Rounded clusters of flowers occur on cultivars officially known as mopheads. The term lacecap, on the other hand, refers to a group of cultivars with flattened flower clusters and two types of flowers: sterile flowers with large, conspicuous petals on the edge of the inflorescence, surrounding the more subtle fertile flowers in the center. There are dozens of cultivars with slight variations in flower color, and this brings us to the most commonly asked question about hydrangeas: How do I change the flower color from pink to blue, or vice-versa?
Flower color in this type of hydrangea depends on the availability of aluminum in the soil. To go from pink flowers to blue—the easier switch—you need to increase the aluminum in the soil, generally by adding aluminum sulfate or using a fertilizer with a content of around 25-5-30. Ideally, your soil pH should be in the 5.2 to 5.5 range. Switching from blue to pink flowers is not as easy and is generally best accomplished in a container. Add dolomitic lime and shoot for a pH of 6.0 to 6.2, or use a fertilizer with a 25-10-10 analysis. The best solution? Be happy with what you get. If you buy a plant with pink flowers at the nursery, remember that it is likely to change to blue when you plant it in Albemarle County.
Occasionally the macrophylla hydrangeas will fail to bloom, generally meaning one of two things. Exceptionally cold weather may have killed the flower buds over the winter; this is unlikely in our climate. Or an over-zealous gardener pruned the shrub in late summer, fall or early spring and cut off the flower buds. If you do feel compelled to prune these shrubs, do so after they have flowered. Breeders have attempted to combat these issues with remontant, or reblooming, hydrangeas; these also flower on the new wood of the season. The most widely hyped cultivar of the rebloomers is the Endless Summer series. Unfortunately, they often don’t live up to their marketing promises. One reviewer referred to them as Endless Disappointment!
There are some hydrangeas where pruning mistakes and flower color are not much of an issue. Hydrangea paniculata, or Panicle Hydrangea, is an old-fashioned shrub you can picture in front of Grandma’s house. This is the largest of the hydrangeas that we can grow, typically 10 to 15 feet. It can be trained into a tree form, but more naturally grows as a multi-stemmed shrub. Regardless of soil type, flowers are white, although they do turn somewhat pinkish as they fade. One cultivar, ‘Limelight’, is promoted for its lime-green flowers, but reports from the South indicate they are essentially white. Caveat emptor. Most Panicle Hydrangeas are mid- to late-summer bloomers, so can generally be pruned in the winter or spring without losing the flowers. One notable exception is the cultivar ‘Praecox’. It flowers earlier, on old wood, so avoid spring pruning. With its large size, Panicle Hydrangea can look somewhat gaunt and out of place in the middle of your lawn. Better to mix it in with other shrubs or put it by the corner of your Victorian house.
Smooth Hydrangea (Hydrangea arborescens) is oddly named, considering there is nothing tree-like about it. Instead, it is a suckering shrub, ranging from 3 to 10 feet tall, but usually on the lower end of that spectrum. It is the only hydrangea native to Virginia, generally found on cool, moist north-facing slopes. If you’re bothered by the dreaded “brown sticks” in the winter, Smooth Hydrangea can be whacked to the ground in the fall and will flower next summer on the new growth. Wild plants have lacecap inflorescences, but most cultivars, including the very popular ‘Annabelles’, sport mophead or snowball flower clusters. Flowers are generally white, fading to lime-green with age, but the recently introduced Invincibelle Spirit is pink. A portion of sales’ proceeds go to breast cancer research.
Another native is Oakleaf Hydrangea (H. quercifolia); although indigenous only to the deep south, it does fine up to Zone 5. Large clusters of white flowers appear in late spring, fade to pink and remain as attractive brown “dried arrangements”. Even without flowers, the oakleaf would be an attractive plant. Flaky, cinnamon-colored stems show throughout the year. In early spring the unfolding leaves are a silvery gray-green. In fall, the leathery leaves turn red, then go to burgundy; some may even persist through the winter in mild years. Several dozen oakleaf cultivars are available, differing primarily in size and shape of the flower cluster.
A neglected hydrangea is the climbing vine, H. anomala, formerly known as H. petiolaris. Climbing hydrangea will cling to trees and structures, and as it matures horizontal branches will develop, giving the effect of an aerial shrub. The delicate white flowers show well against the clean, deep green foliage, and in winter the flaky bark of the “trunk” is attractive.
Most hydrangeas share similar cultural requirements: even moisture in a rich organic soil and partial shade, especially in the afternoon. Panicle hydrangea is tougher than the others, able to take a good deal of sun and drier soils.
One more try at alliteration. “Holy Hydrangeas, Plantman!” Groan…
