General
When to prune is mostly a matter of convenience. We have pruned both
in the fall and early spring and had good results either way. It does
seem that the later and the more harshly you prune that fewer flower
blooms can be expected the next season. This is because most hydrangeas
bloom on "old" wood. With young plants, be sure to prune enough growth
to form them into a good "shape” and no more. This is generally 10 to
20 percent of the growth.
Unlike many of your other flowering bushes (roses and buddleia),
hydrangeas should not be harshly pruned in the spring. Most hydrangea
varieties bloom on old wood and if you cut too much, you won’t get any
blooms. We recommend fall pruning after blooming is done. For us here
in the Pacific Northwest, that means October. This allows for some
active growth before the plant goes dormant.
If you miss fall pruning, you can still prune in the spring. Once
your plant starts to leaf out and your last hard frost is about two
weeks past, you can see the leaf nodes beginning to form. Count back
from the end of the plant such that you have at least three fat and
healthy leaf nodes forming. Prune right above the third one. You may
want to wait until leaves are starting to show before you prune your
macrophyllas so you don’t prune too much.
The Paniculata and Arborescens varieties bloom on new wood so you
may cut them for size every year, spring or fall, whatever is most
convenient for you.
More Pruning Tips
Newly planted hydrangeas need not be pruned except to shape into a
shrub. Once established, hydrangeas can be pruned more severely to
maintain height as described below.
You may prune in the fall after blooming or in the spring after the
hard frosts are over. Remember, the later you prune and the more
drastically you prune, the fewer blooms you'll have. Prune to the first
leaf node of this year's growth as shown in Figure 1.
Figure 1
Cut 1/2" to 1" above a budding node at a 45 degree angle as shown in
Figure 2. These buds will be the new leaves and blooms of your
hydrangea. If you live in an area that is prone to spring frost,
protect these buds with bed sheets or frost cloth (a light felt) on
nights that frost is expected.
Figure 2
Established hydrangeas tend to have branches that die back every
year. These are completely woody branches inside the hydrangea. Cut up
to a dozen of these branches down to the ground as shown in Figure 3 to
spur new growth at the base.
Figure 3
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