Hydrangea paniculata and Hydrangea aborescens produce flowers on new wood, which means that you can cut them back harder without losing this year's flowers. Pruning is not essential, but left unpruned the plant will get taller, with most of the flowers at the top.
Generally, it is safe to prune as much as one-third off of your hydrangea that blooms on new wood.
The hydrangea, which grows on old wood, doesn't need much pruning. If your oakleaf is outgrowing its dedicated space, cut back no more than one-third of the stems after the plant flowers in June or July, says Becker. Weak and dead stems can also be removed in late winter or early spring.
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.
If you need to do a severe pruning to rejuvenate a spindly shrub, you can cut all the branches back to about a foot above the ground in late winter or early spring when it's still dormant. This will cause the plant to produce lots of fresh new growth and you'll still see flowers later that same year.
So the bottom line is that if a hydrangea is too large for the location where it has been growing, the best thing would be to move it and plant a smaller variety in that spot.
Old Wood Bloomers
Hydrangeas that bloom on old wood do not need pruning and are better off for it.
To rejuvenate the hydrangea, remove up to 1/3 of the older living stems down to the ground each summer. This will revitalize the plant. If necessary to control the size of the plant, cut back before late July to allow for buds to develop. Usually the plant will return immediately to its former size.
Once the shrub is established and has a couple of growing seasons under its belt, prune these hydrangeas in the spring down to the ground, or not at all if you want a larger shrub. Flower buds will grow on this season's growth or new wood.
After a day or so of being cut, the blooms begin to wilt. About three days later, they are completely done. But guess what I just learned (from an instagram conversation)? Hydrangeas take in water from their PETALS!
When to prune hydrangeas. Most pruning is carried out in late winter or early spring. However, the climbing hydrangea is pruned after flowering in summer.
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.
Using secateurs, carefully remove old flowerheads just above a pair of buds. Be careful not to cut off any of the flower buds. If the bigleaf hydrangea shrub has been neglected and has lots of overlapping, tangled branches, you can do a harder prune and cut the stems down to the base of the plant.
No need to worry – this is simply a sign that it's time to remove the flowers, a process called deadheading. When you deadhead hydrangeas, you aren't harming the plants at all. Removing the spent blooms triggers flowering shrubs to stop producing seeds and instead put their energy toward root and foliage development.
Too much exposure to full sun for long hours and lack of moisture can cause your hydrangea stems to weaken and touch the ground. Drooping and wilting is your hydrangea plant's way of saying that it is not doing too well and needs your attention!
Use your shovel to make cuts around the hydrangea before actually digging it up. When pulling the plant up, remove with it as much of the rootball as possible. The rootball, dense with fibrous roots and soil, may be very heavy, so enlist help if you need it.
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.
Put Hydrangeas In Water Immediately After Cutting
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!
Keep Them Cozy. Whether or not hydrangeas need protection depends on how cold the winter temperatures drop. If the air temperature doesn't go below 0 degrees (zone 7) there is no need for winter protection. In colder climates, wrap or completely cover marginally hardy hydrangeas.