I have searched the Internet on the topic of trimming hydrangeas and am still a little confused. My plants are huge and I want to cut them back, but not lose the flowers this summer.
How you prune your hydrangeas depends on what type you have. The old-fashioned pompon variety (Hydrangea macrophylla) blooms on previous year’s growth, or what is referred to as old wood, while Hydrangea paniculata and Hydrangea arborescens set flowers on the current year’s growth.
Let me start with the old-fashioned type as they are the most popular. Also included in this group are lacecaps and oakleafs (H. quercifolia). Little pruning is required with these hydrangeas. In fact, improperly pruned bushes can result in bushes not producing any blooms. In late winter you can tidy up the plant by removing old flower heads and cutting back any dead wood to ground level. Now if you live in a region that experiences topsy-turvy springs with warm spells and cold snaps, wait to prune until after the last frost date. As you prune, cut the faded blooms back to the first set of leaves or leaf buds. If you have a mature shrub that has grown dense in the center, it is a good idea to remove about 1/3 of the oldest stems. This may sacrifice some of the coming summer’s blooms, but it will open the plant up to light and circulation, making it a happier and healthier plant.
Things get a little trickier when it comes to reducing the size of the plant. You have two options. The first option is to cut the plant back in late winter. This will mean that the hydrangea won’t bloom until next year, but I find it much easier to prune at this time because the bones of the shrub are more visible. Simply cut mature stems back by about 1/3. If the plant is completely out of control, cut all the stems back to about 1 1/2 feet tall. Over the course of the summer thin out the new shoots to avoid overcrowding.
The second option is to prune your old-fashioned hydrangea immediately after the flowers fade in the summer. The timing on this is important because the plant needs enough time for the new shoots to harden off before the first frost in fall. For this type of summer pruning, reduce the unwanted height by about 1/3.
Pruning H. paniculata and H. arborescens is a much less complicated task because they bloom on new wood.
‘PeeGee’ is a popular variety of H. paniculata. It produces large cone shaped, creamy white blooms that fade to a nice coppery pink in the fall. ‘PeeGee’ is often grown in a tree form or what is referred to as a standard. This is a single stalk with growth weeping from the top. In late winter cut the stems back to two buds above the base of the stems.
I grow H. arborescens ‘Annabelle’ in my garden. It produces huge, white, pompon shaped blooms in late summer. ‘Annabelle’ is a good choice for people living in both cold regions and warm climates. It is less finicky than H. macrophylla, which is only hardy to zone 5 and also doesn’t do well in areas that don’t experience a dormant season. In late winter I simply cut the plant back to varying heights of 1 to 3 feet from the ground. This will help the plant to maintain its informal shape.