Why pink bigleaf hydrangeas won’t bloom in summer time

The massive, pink mophead blooms of bigleaf hydrangea are one of many joys of summer time for Chicago gardeners. What a disappointment when these blooms fail to fluff!

“Bigleaf hydrangeas simply aren’t totally dependable in our local weather, as a result of generally the flower buds don’t make it by the winter,” mentioned Julie Janoski, Plant Clinic supervisor at The Morton Arboretum in Lisle.

Buds of bigleaf hydrangea (Hydrangea macrophylla) are fashioned in late summer time and should survive all winter to bloom the next summer time. “They aren’t particularly nicely protected, so even a single day of extreme chilly is sufficient to kill them,” Janoski mentioned. Useless buds will seem blackened, and they’re going to by no means open. The hydrangea might produce considerable inexperienced leaves in spring however no blooms.

Gardeners will be confused as a result of another acquainted species of hydrangea do bloom reliably: easy hydrangea (Hydrangea arborescens), together with the favored Annabelle cultivated selection, and panicle hydrangea (Hydrangea paniculata), together with the Tardiva selection. “These hardy hydrangeas don’t kind their flower buds till spring, so the buds are by no means in danger from winter chilly,” Janoski mentioned.

In gardening parlance, shrubs that set their flower buds on stems fashioned within the earlier 12 months and overwinter them are mentioned to “bloom on previous wooden.” People who develop their flower buds on new twigs within the spring or summer time of the identical 12 months they bloom are mentioned to “bloom on new wooden.” Roses are a traditional instance.

[ Garden guide: Everything you need to know about growing hydrangeas ]

Numerous hydrangea species are iffy as a result of they bloom on previous wooden, akin to oakleaf hydrangea (Hydrangea quercifolia), climbing hydrangea (Hydrangea petiolaris) and mountain hydrangea (Hydrangea serrata).

In some climates with extra equable winters, such because the Atlantic states the place climate is moderated by the close by ocean, these crops’ buds are much less more likely to be killed. The risky and sometimes harsh Chicago local weather is extra dangerous for them. After a light winter they might bloom abundantly, however after a chilly winter — or perhaps a largely gentle winter with a bud-killing chilly spell — they might not bloom in any respect.

So as to add to the confusion, some newer forms of bigleaf hydrangea, such because the Limitless Summer season and Let’s Dance sequence, and mountain hydrangea, such because the Tuff Stuff sequence, have been bred and chosen to bloom to various levels on each previous and new wooden.

“Even when the buds on previous wooden are broken over the winter, these varieties can develop some new wooden in spring that can set flower buds,” Janoski mentioned. “It’s possible you’ll not get as many blooms as you’d after a light winter, however you’ll seemingly get some.”

There’s one other widespread motive that hydrangeas fail to bloom: “Typically the flower buds get minimize off when the gardener is pruning in winter,” she mentioned.

In case you prune a plant in winter that blooms on previous wooden, akin to bigleaf hydrangea, forsythia, lilac, mock-orange, or ninebark, you’ll be eradicating the flower buds together with branches. “To be secure, wait to prune a spring- or summer-flowering shrub till after it has bloomed,” Janoski mentioned.

Vegetation that bloom on new wooden, akin to easy hydrangea and panicle hydrangea, will be pruned in winter with impunity.

How are you going to know what to do? “Determine your crops,” she mentioned. It’s not sufficient simply to know you will have a hydrangea, as a result of completely different species of hydrangea develop in another way and want completely different care. “That you must discover out precisely which species of hydrangea you will have.”

The Plant Clinic may help you determine your crops and learn how to take care of them so that you get essentially the most magnificence and satisfaction out of your backyard.

For tree and plant recommendation, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a workers author on the Arboretum.