Pruning Hydrangeas

Tuesday, January 16, 2018 3:42 PM

I am confused as to when to prune hydrangeas.   I have heard to prune in the spring while others say the fall.  Which is correct?   Diane W., Owasso

Actually, both answers are correct as it depends on the type of hydrangea. 

First, hydrangeas generally do well with no pruning, but there are several reasons for gardeners to get out the shears.  Only prune a plant when there is a reason — don't prune simply because everyone else seems to do it.  Your plant may be a candidate for pruning if it is too large or too dense, has dead or diseased limbs, or if you want to try to increase blossoming.

When to prune depends on the type of hydrangea and its blooming time.  There are four species of hydrangeas commonly planted.  The most popular is the Hydrangea Macrophylla (Bigleaf Hydrangea).  This species is divided into Mophead and Lacecap blossom types and are usually blue to pink.  The white-blossomed Oakleaf Hydrangea (Hydrangea Quercifolia) is next most popular.  Both of these hydrangea species bloom in early summer on buds formed during the previous late summer and fall.  Because spring-blooming hydrangeas bloom from buds grown during late summer and fall of the previous growing season, pruning these hydrangeas before spring will cause all the blossom buds to be lost.  Instead, they should be pruned immediately after blooming and only up to early July before next year's buds are formed. 

Hydrangea Arborescens ("Annabelle" and others) and Hydrangea Paniculata ("PeeGee" and related) are less common.  They have blossoms that are initially white and bloom on same-season buds formed during the summer.  Prune these after summer flowering and up to early spring.

While older varieties of Macrophylla hydrangeas are only spring bloomers, some of the newer cultivars bloom in spring, as well as summer, and into the fall.  The popular Endless Summer, a true Mophead, was the first of several re-blooming hydrangeas put in production in recent years.  Because it is capable of blooming on both old and new buds, the pruning of these after the spring or late summer flush of blossoms is acceptable.  There is no true consensus for the best pruning time, as they are very forgiving.

Pruning should not be confused with dead-heading, or snipping off the spent blossoms as they occur.  This can be done anytime and likely increases the number of subsequent flowers, especially in the re-blooming varieties.

It takes hydrangeas about three years to establish a good root system and, in an ideal world, it would be best not to prune during this time other than to remove dead wood or poorly placed branches.  One exception is that older plants may be rejuvenated by pruning one-third of the oldest stems to the ground in late winter regardless of their blooming habits.

For more information on pruning, consult OSU fact sheet HLA-6409 on "Pruning Ornamental Trees, Shrubs and Vines" which available on the newly updated Tulsa Master Gardener web site or at the OSU Extension Office.