GOSHEN, Ind. — There are two question Master Gardeners are often asked at the fair and on the Answer Line: 1) why doesn’t my hydrangea bloom? And 2) how can I make my hydrangea change from pink to blue or visa versa?
There are three key reasons hydrangeas fail to bloom: too much shade, improper pruning, and weather related damage. It is important to know which hydrangea species or cultivar you have to provide the best care for the plant and to enjoy the blooms for years to come.
Most species of hydrangea benefit from some shade, but too much shade will reduce flowering. Bigleaf, oakleaf, and smooth hydrangeas will usually perform well on the north side of a house. Panicle hydrangea does well in full sun. A general rule of thumb is morning sun with afternoon shade. If your hydrangea used to bloom well, but over the years blooms have become sparse, evaluate whether the growth of nearby trees has reduced the amount of sunlight that reaches the hydrangea.
Improper pruning will also affect blooms. Pruning too late or too much will remove next year’s flower buds. Bigleaf and oakleaf hydrangeas, which flower on previous year’s growth, should be pruned shortly after flowering is complete and should be cut just below the flowers. Panicle and smooth hydrangea flower on the current year’s growth. They do best if cut back every year in late winter or early spring before leaves appear
Weather conditions may also play a role in hydrangeas not blooming. Early fall freezes that occur before the plant is completely dormant, extremely low winter temperatures, and late spring freezes may damage flower buds and reduce flowering.
The ability of some hydrangeas to change colors is fascinating. White hydrangeas (Smooth, Oakleaf, Climbing and Panicle) will not change color no matter how hard you try. Bigleaf and Mountain hydrangea are the most likely to change color if the pH around the plant is changed. Flowers can be blue if the pH is below 5.5, or pink if the pH is above 6.5. If the pH is between 5.5 and 6.5, you can get some flowers that are a bit of a mash up between blue and pink. It is important to note that not all Bigleaf and Mountain cultivars change flower color with a pH adjustment.
Want more information about hydrangeas? Check out this handy chart from Ohio State Extension at https://goo.gl/Amo7dM
If you have other plant questions, please feel free to call our office at 533-0554. We have Master Gardeners working a part time Answer Line most days of the week, and they would love to help you.
— Purdue Extension Elkhart County
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