Q: My Nikko Blue hydrangea is about 5 years old. It looks fantastic, but blooms less and less each year. It has lots of healthy leaves, but few flowers. Do you have any suggestions?
— Adrienne Laya, New Lenox
A: The Nikko Blue hydrangea is at the northern edge of its hardiness zone in Chicagoland. This hydrangea blooms on large buds formed on growth from the previous season. After a harsh Chicago winter, a large number of flower buds may be lost, resulting in diminished flowering. Late-spring frosts and deer browsing can also decrease flowers. If the plant dies back to the ground after a very cold winter, there will be no flowers in spring. The hydrangea will resprout from the base and develop healthy green foliage but no flowers. It is likely that your Nikko Blue hydrangea is losing flower buds from winter cold, late spring frosts or deer eating the buds. Mulching the plants and wrapping with burlap may help.
Pruning at the wrong time can also remove flowers. Do not prune them back hard in late winter or early spring as is commonly done with Annabelle hydrangeas. As the flower clusters of the Nikko Blue hydrangea are fading in late summer, prune just below the flowers if desired. Then in spring, prune just above the first set of buds. Give the plants extra time in spring to leaf out before determining whether or not the stems are dead.
There are new varieties of big-leaf hydrangeas that flower on both old and new wood and should be more reliable in flowering. Some of the new cultivars are Endless Summer: “Twist-n-Shout” and “Blushing Bride” are two Endless Summer varieties to consider. Soil pH affects the flower color, producing more blue in acidic soils and pink in slightly acidic to alkaline soils. Add elemental sulfur in spring and fall to lower the pH of your garden soil surrounding the hydrangeas.
Tim Johnson is director of horticulture for the Chicago Botanic Garden in Glencoe. Send questions to: Gardening Q&A, Sunday, Chicago Tribune, 435 N. Michigan Ave., Chicago, IL 60611-4041; e-mail to sunday@tribune.com.
