Wait! Put down those pruning shears and back away from your hydrangea! If you are concerned about those beautiful shrubs blooming to perfection in the spring, you need to understand their care. If they are looking gangly and out of control and you are just itching to cut them back, down or otherwise, read on to see what kind of hydrangeas you have in your garden, and how you should approach their pruning.
Old Growth vs. New
Your first step is to recognize if your hydrangea is blooming on old growth or new. Are the blooms appearing on new green shoots that came in this year, or on old, woody branches from last year? If the answer is new growth, put down the shears until late winter or early spring. If it bloomed on old growth, then late summer is the time to prune. Be on the look out for new-forming buds! Big leaf and oak leaf hydrangeas form buds the year before they bloom. Use caution to not chop off the buds of next spring's flowers.
Examples of old wood hydrangea are big leaf, oak leaf, climbing and mountain. Call it dead-heading if you like, but these can be pruned right after blooming. Remove some older stalks in order to control the gangly appearance of the shrub, and to control its shape and size. Again, take care not to disturb new buds.
Panicle and smooth hydrangeas are examples of those that bloom on new wood. These types can be "hard pruned," which is taken down to 18" above the ground. Aggressive pruning in the early spring may even enable the hydrangea to produce more blooms.
And just when you think you've "got it," be aware that some new hybrids of hydrangea will bloom on both old and new wood. Some popular examples of these are "Endless Summer," a mop head hydrangea, and "Pinky Winky," a panicle hydrangea that is sometimes seen as a tree variety. These need no pruning, but will benefit from dead-heading right after blooming. If pruning to limit size and growth, watch for buds before cutting stalks, and cut right above the bud.
Timing is Everything
Make sure that you do not prune after the temperature drops and your garden experiences its first frost. Pruning during very cold temperatures can cause something called die-back, which happens when the pruned stalk is subjected to freezing temperatures before healing over during milder temperatures. Make your cuts at a 45-degree angle to the stalk, which promotes better water run-off, sealing off and can help ward off disease.
To sum up, there are six main types of hydrangeas. Here is a list, whether they grow on old or new wood, and the best time to prune:
Big Leaf/Mop Head/Lace Cap Old/New wood Late winter
Oak Leaf Old wood Summer/Late summer
Panicle Old/New wood Late winter/Early spring
Smooth New wood Late winter/Early spring
Mountain Old wood Summer/Late summer
Climbing Old wood Summer