Hydrangea species that bloom in early spring should be cut back just after they finish flowering in May or June. Those that bloom in the summer should be pruned while they are dormant in December through February. Dead wood can be removed at any time of the year.
Prune back stems to just above a fat bud — called a heading cut — in fall, late winter or spring. These plants have conical-shaped flower heads. I recommend leaving the dry, tan flower heads on the plant to provide some winter interest in your landscape, so I wait to prune these until late winter or spring.
Generally, it is safe to prune as much as one-third off of your hydrangea that blooms on new wood.
To reduce the size of a hydrangea that blooms on new wood, cut off about one-third of each stem in late fall or early spring before it begins to leaf out. If your hydrangea blooms on old wood, prune right after it has bloomed when the flowers are fading.
It is easy to grow these hydrangeas because they bloom every year regardless of how they are cared for or treated. They can be pruned to the ground in the fall and they will emerge in the spring with bountiful blooms. However over a period of time this drastic pruning may cause the plant to slowly weaken.
In late winter or early spring, these shrubs can be cut all the way back to the ground. Smooth hydrangeas will produce much larger blooms if pruned hard like this each year, but many gardeners opt for smaller blooms on sturdier stems.
Old Wood Bloomers
Hydrangeas that bloom on old wood do not need pruning and are better off for it.
Hydrangeas do not require strict reqular pruning; simply keep them healthy by removing dead wood and they will grow and flower well.
So these shrubs should be pruned immediately after their flowers fade. Conversely, if the shrub flowers on new wood (stems developed during the current season), its buds are set within the season, so the shrub should be pruned in early spring before that new growth emerges.
If you prune them at the wrong time, you could risk cutting off all the flower buds and ending up with no blooms that year.
Plants grow toward their light source. Without sufficient sunlight, Hydrangeas will reach for the sun, resulting in the top areas of the plant becoming denser than the bottom. Hydrangeas grow best when they get full sun in the morning and filtered light throughout the day.
In general, plants should be pruned to improve appearance not control size. I repeat that because it's important: Hydrangeas should be pruned to improve appearance, not control size. The mature hydrangea is a shrub that cannot be made smaller.
As soon as hydrangeas are cut, the stems should immediately be put into tepid water. And adding a little bit of flower food to it would be a great idea too. Use a sharp knife or clippers to cut each stem on a diagonal and submerge! Cut hydrangeas in the morning and choose only the most mature blooms.
Here are the four most common types of hydrangea: Panicle hydrangeas, sometimes referred to as Pee Gee Hydrangeas or Hydrangea paniculata, are a variety that blooms on new wood only. This group can be pruned in fall or very early spring, but we highly recommend waiting until the spring to reduce risk of injury.
Lay down 6–8 inches (15–20 cm) of mulch around the plant base. Hydrangeas require a thick layer of mulch to protect them properly throughout the winter. Scatter your mulch materials to cover the ground around the base of your plants. Make sure that the mulch is at least 6 inches (15 cm) high.
Without going through the deadheading process, hydrangeas will not produce as many flowers and the few produced may not grow as big to their full potential.
But when to prune them? Prune fall blooming hydrangeas, or old wood bloomers, after they bloom in the summer. If you prune old wooded hydrangeas in fall, you are cutting off next seasons blooms. Summer blooming hydrangeas, or those that bloom on new wood, are pruned in the fall, after they stop blooming.