5 Tips for Growing Gorgeous Hydrangeas
These classic flowering shrubs are prized by homeowners from North to South. Here's how to get them to bloom their best
They're a summertime staple in yards across the country: big orbs of blue on the outstretched arms of leafy shrubs. These so-called mopheads (a type of H. macrophylla) were imported from Japan, China, and Europe in the 19th century. But there are also delicate lacecaps that have flat heads dotted with color and ringed with four-petaled florets, and panicle hydrangeas with white cone-shaped flowers. There are also easy-care species native to the U.S., such as the shade-tolerant oakleaf hydrangea and cold-hardy smooth hydrangea.
Need a little help coaxing your own hydrangeas to perform better? We've got answers to the most common queries about growing these garden favorites.
Shown: Many H. macrophylla varieties can produce pink to deep blue blooms (even on the same plant), depending on the soil's pH.
Q: Often my hydrangeas just don't bloom. Am I doing something wrong?
A: Take a good look at how they're sited. Hydrangeas generally need some sun and like some shade. In the South, nurseries grow them under pines or shade houses to filter sunlight. "For most hydrangeas, the farther north they are, the more sun they can stand," says horticulturist Michael Dirr. "In the South, they can get away with just three hours of sun." Hydrangeas in Southern gardens should be planted in locations with morning sun and afternoon shade; in the North they can do well in full sun as long as they get plenty of water and aren't subjected to dry winter winds. Temperature is as much an issue as sun, particularly for mopheads, which are susceptible to drooping from heat stress. They love a coastal setting, where breezes dissipate the heat, and thrive in the salty air. If full sun exposure and high heat are issues, you might try another old-time favorite, peegee hydrangea (H. paniculata 'Grandiflora'), which can withstand those conditions. If, on the other hand, your yard is short on sun, try oakleaf hydrangea, which prefers partial shade.
Another issue that can affect bloom is a late-spring or early-fall cold snap; the buds on bigleaf hydrangea (H. macrophylla) are particularly vulnerable because they flower on the previous year's growth. If unpredictable frosts are a problem where you live, consider two cold-hardy types: smooth hydrangea, which is native from New York to Florida and as far west as Arkansas; and peegee hydrangea, which is also the most drought tolerant. A popular native, H. arborescens is prized as a reliable bloomer in cold climates.
Last, consider how and when you prune. If you're cutting off more than just dead branches or spent blossoms in fall or early spring, you're removing the old wood, which carries the new season's buds for H. macrophylla "And I always use half the amount of fertilizer recommended on the label," says Dirr. "That way you'll be encouraging blooms and not more leafy growth."
Shown: Usually seen as the classic white 'Annabelle,' this pink 'Bella Anna' (shown) is a brand-new hybrid that reblooms all summer.
Q: That raises the question: Should I be pruning at all?
A: If your hydrangeas are sited correctly, with enough room to grow, the only pruning required is to remove dead wood—be sure to take it off at the base of the plant if the whole branch is dead—and spent flowers. In Dirr's experience, all hydrangeas benefit from regular dead-heading to encourage more blooms. Left unpruned, they will produce fewer flowers because of a growth-inhibiting chemical released by the terminal bud at the tip of the stem. Don't prune past August, though, because any new growth is susceptible to an early-fall freeze.
"Whether to prune hydrangeas is often debated, but studies have shown that dead-heading spent flowers definitely encourages more and bigger blooms," say horticulturalist Michael Dirr.
Shown: TOH landscape contractor Roger Cook clips large flowers from a mature peegee. These tree-like shrubs reach up to 25 feet tall, with white to pink conical-shaped, mid-to-late-summer blooms.
Q: What's the story with reblooming hydrangeas?
A: One way to guard against the vagaries of mistakenly cutting off buds or losing them to a cold snap is to grow some of the newer reblooming hybrids. These have become staples at home centers since their first introduction, in 2004. Some to consider are 'Endless Summer,' a blue mophead, and 'Twist and Shout,' a pink to blue lacecap (go to Endless Summer Collection for stores). 'Let's Dance Moonlight' is a new reblooming pink mophead (go to Monrovia for stores). These hybrids bloom throughout the summer on both the current and past year's growth, so they will produce blooms on the new growth even if the old growth is nipped in the bud by cold temperatures.
Shown: The big blue 'Endless Summer' hybrid mophead (shown) reblooms all season.
Q: Is it okay to transplant my hydrangeas now?
A: It's easy to move hydrangeas. Just prune mature shrubs down to a manageable size, and dig up as large a root ball as you can handle. Place it in a new hole, backfill, add a slow-release fertilizer, water well, and top dress with 2 inches of organic compost. Though you can move a hydrangea anytime, it's best to do so when it's dormant, in early spring or late fall. For oakleaf and panicle hydrangeas, dormancy is key.
Shown: Oakleaf varieties produce spectacular fall color and late-summer white to pink blooms.
Hydrangeas respond well to several propagation techniques, including layering and dividing. But Dirr's method for rooting softwood cuttings in summer will yield a bunch of new plants in about four weeks.
To do it, locate a stem of softwood between the hard, woody growth at the bottom of the plant and the fleshy green tip by bending it; softwood should snap cleanly. Cut a softwood shoot that has several leaves. Trim it into 5-inch-long pieces that each have a leaf toward the top. Remove extra leaves; Dirr goes a step further and cuts the remaining leaf in half to minimize evaporation (and the need for watering). Dip the other end in powdered rooting hormone; plant the cuttings in trays filled with a soilless mix and perlite. Cover with a plastic bag, and stash in a shady location, misting regularly to keep the leaf hydrated. After four weeks, tug on it to check for roots; once roots are developed, transplant to a bigger pot and feed with a slow-release fertilizer. By next spring, cuttings will be ready to go in the ground.