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Prune them in the spring. Prune them in the fall. Prune them aggressively. Don’t prune them at all. Conflicting advice about hydrangea care can be a conundrum for the uninitiated. And to make matters worse, it’s all true. Two of the four species of hydrangeas that thrive in Central Virginia are native to North America, and two originated in East Asia. Each has its own growth habit, sun preferences and pruning requirements. No wonder this beloved centerpiece of the summer garden is a blooming enigma.
Enter Richard Waiton, who leads the “Hydrangea Walk & Talk” tours at Lewis Ginter Botanical Garden during June and July, when the hydrangeas he loves are in full bloom. His passion for the plants is palpable as he breaks it down for curious visitors. Here are his recommendations.
Japanese Shrub Type: macrophylla (“large leaf”) and serrata (“toothed leaf”)
This is the classic, periwinkle blue pompom such as “Nikko Blue” or “Endless Summer,” as well as the delicate lacecap like “Blue Wave,” with its flat, fringed flower heads. “Treat them like azaleas,” Waiton recommends. “Plant them in dappled shade, in well-drained, moist, acidic soil.” With a few exceptions, Japanese shrub hydrangea bloom on old wood. The buds form at the end of the growing season. They winter over, and then mature to full bloom the following summer. If you must prune them, selectively clip some of the longest stems at the base of the shrub to preserve next year’s display.
Because bloom color is sensitive to soil acidity, blue Japanese hydrangeas require soil pH of 5.5 or lower. If you want a deeper blue, amend the soil with horticultural sulfur or aluminum sulfate to increase its acidity in early spring. To force a pink hydrangea to be more pink or red, add limestone to the soil. “Buy a variety that wants to be the color that you want it to be,” Waiton says. “You can adjust the color from there, but only slightly.”
North American Type: quercifolia (oakleaf hydrangea)
Oakleaf hydrangeas offer year-round interest. Their creamy white, cone-shaped flower heads age to pink and then rusty brown in winter, while the leaves evolve from light green to red, then purple and bronze, with silvery undersides. Native to Alabama and the southeastern United States, they are relatively tolerant of drought and shade, blooming on old wood. “Give them adequate space and basically ignore them,” Waiton recommends with a smile. “Snow Queen” and “Snowflake” are standout varieties.
North American Type: arborescens (smooth hydrangea)
“Annabelle” is the best-known of this variety; the larger, sturdier “Incrediball” is perhaps the most impressive. Native to the southeast and midwestern United States, Annabelle was first spotted by two women from Anna, Illinois, who were riding horseback in the woods. Almost 50 years later it came to the attention of a local university professor, who named it after those two “belles” and the town they called home. Waiton advises treating arborescens like butterfly bushes — plant them in full to partial sun and prune lightly (to shape them) or to the ground (to encourage new growth). They bloom on new wood.
Upright Shrub Type: paniculata (panicle or PeeGee hydrangea)
Paniculata is one of the most winter-hardy hydrangeas. Native to China, they are graced by upright, cone-shaped white flower clusters whose weight coaxes branches into a gentle arch. Waiton suggests planting them in full sun, like crape myrtles, and pruning only if needed, in late winter or early spring, as they bloom on new wood. His favorites are “Limelight” and recent dwarf introductions such as “Bobo.”
Susan Higgins is corporate and foundation relations director at Lewis Ginter Botanical Garden. She writes about what she learns and loves in the garden.
