On summer days in many neighborhoods, the big, showy white flower clusters of panicled hydrangeas seem to be everywhere.
These shrubs are tough, adaptable and hardy, so it’s no surprise they’re popular with gardeners. “Some kinds of hydrangeas don’t bloom reliably after a Chicago winter, but you can count on panicled hydrangeas,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle.
Although they prefer moist soil with plenty of organic matter, panicled hydrangeas can handle a range of soils, including the alkaline clay soils so common in the Chicago region. They can thrive in full sun or in locations that are shaded for part of the day.
The straight species of panicled hydrangea (Hydrangea paniculata) can grow 15 to 20 feet high, as tall as a small tree but with a wider, shrubby habit. “It’s a plant that needs a big yard,” Yiesla said. A popular older garden variety is Hydrangea paniculata ‘Grandiflora,’ known to some gardeners as a “PG” or “peegee” hydrangea.
In recent decades, as gardeners with less room have sought hardy, easy-care plants, plant breeders have developed many new cultivated varieties in a wide range of sizes. Some are just a couple of feet tall and can nestle in a bed among the perennials. “There really is a cultivar to fit just about any space,” she said.
Color is another new development. On many cultivated varieties, the fluffy blooms — each an elongated cluster of many small flowers called a panicle — are cream or white against dark green leaves, like the original wild species. Other new cultivars have been bred to have panicles that are partly to totally pink, or that start out white and turn pink as they age.
At the Arboretum, you can see 25 kinds of both white and pink panicled hydrangeas in the gardens and collections. In the Temperate Asia Collection is the original white-blooming Hydrangea paniculata, whose wild origins are in China and Japan. To learn about cultivated varieties the Plant Clinic recommends, go to mortonarb.org/search-plants and search for “panicled hydrangea.”
Depending on the weather, most varieties start to bloom in mid- to late June and hold onto their flower panicles all summer. In fall, the panicles dry on the plant and can be a source of interest even in the gray winter.
These hydrangeas naturally grow as well-branched shrubs, but garden centers sometimes sell them trained into a tree form, or standard, with a single trunk. Those can be suitable for formal gardens or in a small space.
Hydrangea paniculata blooms reliably because it does not develop its flower buds until after the bud-killing cold of winter is over. “The plant blooms on new wood — the branches that sprout in the spring,” Yiesla said. Another type of hydrangea that also is winter-hardy because it blooms on new wood is smooth hydrangea (Hydrangea arborescens), including the popular variety Annabelle.
On the other hand, a hydrangea species that can sometimes disappoint Chicago-area gardeners is the bigleaf hydrangea (Hydrangea macrophylla), known for having big blue blooms when grown in acid soil and popular in the eastern United States. Its buds are vulnerable in winter because they form on the branches in summer and must survive through the cold to bloom. That’s more likely in the East, where winter weather is relatively mild or where there is reliable snow cover to protect the buds. “In Chicago, one bitter cold night can kill them all,” Yiesla said. No blooms.
To get around that, consider bigleaf hydrangea cultivars that have been bred to flower both on old wood and on new wood, or choose hardy species such as smooth hydrangea or panicled hydrangea.
Since panicled hydrangea does not have flower buds in winter, its bloom won’t be affected if you prune it during the dormant season. Pruning can encourage vigorous growth and larger flowers or control the shrub’s shape and size. “Nowadays you can choose a right-sized cultivar to begin with and you won’t have to prune as much,” she said.
With so many choices among panicled hydrangea varieties, the shrub is an easy way to bring summer bloom into many home landscapes.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
