Overgrown branches are very hard to prune back into the former tree-shaped form.
Panicle Hydrangea (Hydrangea paniculata and cvs., Zones 3–8) You may have purchased this plant either as a shrub or as one with an elevated head called a tree form or “on a standard” in the nursery industry. Both can be pruned in the same way.
This is unlike other varieties of hydrangeas.
When to prune: Early spring is best, when the first green new growth appears but the threat of frost has bushhaul.barted Reading Time: 2 mins. Feb 10, You would normally prune panicle hydrangeas for the following reasons: to create a more pleasing shape, to control growth, to remove dead flowers, to remove crossing branches, or to eliminate dead, damaged, or diseased stems.