Pruning Oak Leaf Hydrangea

(Question)

I have a Oak Leaf Hydrangea which was planted about 5 years ago. Its grown to about 5 feet in all directions and has in the past been very healthy producing large lovely flowers in late July. It is always late to get foliage and I have to remind myself to be patient. Its situated in a garden bed that is in light shade and mostly receives afternoon light. This year however I only see some leafs emerging on the lower branches. Should I wait longer before pruning? Should I cut it right back to where the growth starts? Will it come back?

(Answer)

Thank you for your inquiry to Toronto Master Gardeners.

Yes, you should wait until July to prune any living branches but those that are clearly dead can be cut back any time.  Here is the explanation:

The reason for  your plant’s failure to show signs of flowers is probably weather related.  You can blame it on the prolonged cold weather we endured this past winter.   Oakleaf Hydrangea (Hydrangea quercifolia) blooms on old wood.   The buds are developed in the previous fall for the current summer’s blooms.    Since oak-leaf hydrangeas are native to S.E. North America, where winters are generally milder, the buds that were formed last year were likely killed by our frigid arctic temperatures.  Assuming that you did not prune your plant last year or this spring, the buds simply froze and therefore could not produce any flowers.

Pruning should be done after the shrub has had a chance to produce whatever flowers it can.  This is usually done in July before it sets the buds for the following year’s blooms.  Buds can develop as soon as August, so make sure that it is pruned by then.

Two excellent guides to pruning all sorts of shrubs and trees are:

  • Pruning Made Easy: A gardener’s visual guide to when and how to prune everything, from flowers to trees  by Lewis Hill
  • The Pruner’s Bible: A Step-by-Step Guide to Pruning Every Plant in Your Garden by Steve Bradley

Your hydrangea may also have suffered some die-back of branches.  Dead stems can be cut down to the ground at any time of year and up to 1/3 of old leggy stems can be cut down after flowering to rejuvenate the plant.

There is a great deal of information about Oak-Leaf Hydrangea on our website.  Here is one sample answer, from which I took some of my information. https://www.torontomastergardeners.ca/index.php/askagardener/when-to-prune-oakleaf-hydrangea/
For Q & A and other resources, including Gardening Guides, go to the home page and scroll down.  On the right you’ll see categories of our most frequently asked questions.