Freeze damage on hydrangea shrubs--winterkill

Bigleaf hydrangea, like my blue blooming mophead hydrangea (Hydrangea macrophylla), set blooms near the end of the previous growing season. One winter season was quite mild for my area, setting record high temperatures in March. The hydrangea shrub started growing even before the coldest days of winter had past. Our local weather service advised us of freezing temperatures for the evening. I smartly covered vegetables such as broccoli and lettuce, but never thought about the hydrangea. It never needed protection before. I have learned my lesson. Below is a picture of what one night of sub-freezing temperature can do to a hydrangea. It is called winterkill.

What you are seeing is a mixture of brown or black dead leaves that were a result of the freezing temperatures and healthy, new leaves that opened the days following the freeze. Because the dead leaves are unsightly, I decided to prune this hydrangea. I figured I had two options: prune only the damaged portion, which would give the shrub and uneven appearance, or prune the entire shrub to restore a uniform shape. I love hydrangea blooms. Each summer I have a continuous supply of blooms for floral arrangements plus a supply to dry for winter decorations. Knowing that pruning mophead hydrangea in the spring will cut off flower buds, I decided to prune out the ugly dead leaves and not touch the remainder of the shrub. I hope that some of the unscathed cane will produce blooms.

I pruned each stem individually. Looking for leaf buds, I made the cut at the location shown by the arrow. The cut was into healthy cane between the buds and the dead tip of the cane. The amount clipped off varied from as little as 1 inch up to 6 inches. Overall, I pruned about half of the shrub. I will update you this summer on whether or not the shrub bloomed this season.

UPDATE: In late spring, blooms displayed around the bottom and the back side of the hydrangea shrub. The area I pruned filled out with new leaves, giving the shrub a perfect dome shape. Though part of the shrub will not bloom this season, I know that it will bloom next year so no permanent harm was done following the winterkill.


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