How to Prune Hydrangeas
A popular flowering shrub, hydrangeas are easily recognizable for their lush blooms and hardy leaves. These perennials do best in well-drained soil in USDA zones 5 to 9 and grow from 3 to 6 feet tall. Most species need pruning to maintain their shape and produce flowers every year, but even if yours doesn't need it, you may want to prune for aesthetic reasons.
Before you get out the shears and start snipping, identify your shrub; different species have different pruning schedules. Prune at the wrong time, and you could be inadvertently cutting into next season's flowers.
The Big Leaf (Hydrangea macrophylla)
Two popular varieties, Mophead and Lacecap, come in blue, pink, and purple, with thick, shiny leaves. Mophead produces large, ball-shaped flower clusters, while Lacecap's clusters are flat and delicate. They bloom on old wood (stems that have been on the bush since the summer before) and should be pruned in the summer when the flowers have started to fade but before August hits. A bush can be trimmed by cutting back stems close to a node. If a plant is overgrown, prune back about one-third of the older stems almost to the ground.
Oakleaf (Hydrangea quercifolia)
This species has leaves that look like they belong on red oak trees and flowers that open white and then turn pink. The hydrangea, which grows on old wood, doesn't need much pruning. If you want to control its shape or size, clip it in the summer before August when flowers' once-vibrant colors begin to fade.
Smooth (Hydrangea aborescens)
One variety, Annabella, has big flowers that are actually made up of many small individual blooms. They start out green but turn white a few weeks later. This species' leaves are thinner than Mophead's and Lacecap's. Since it blooms on new wood (stems that have grown during the current season), prune in early spring before any flower buds have appeared.
Peegee and Limelight (Hydrangea paniculata)
This white species, which blooms on new wood, is most often cone-shaped and sharply pointed. It comes in many varieties, from small shrubs to small trees. Its leaves are rough and thin. Prune in early spring before it starts flowering.
Tree of Heaven and Mountain (Hydrangea serrata)
Tree of Heaven has a similar look to Mophead, but it is a smaller shrub with narrower, pointed leaves. The flower, which blooms on new wood and can be pruned at any time after the new growth has started, is affected by a soil's pH: It produces lilac to pink flowers in alkaline soil and blue blossoms in acidic soil.