Smooth hydrangea (left), big leaf hydrangea (middle), panicle hydrangea (right). Only the first and last should be pruned in spring.
It’s unavoidable. A few warm days, birds chirping, snow melting, and crocuses sprouting can only mean one thing. Time to get those pruners out and do a little trimming.
When it comes to hydrangeas, however, incorrect pruning is the biggest reason for lack of flowers. That’s because we prune them at the wrong time. So, let’s get it straight once and for all.
Pruning New Wood
The ones you can prune in early spring are those that flower on stems they will grow this year, i.e. on new wood. Easier said than done, since most of us don’t know which ones we have and what kind of wood they have. Let’s drill down a little deeper to figure that out.
Flower Shape and Foliage Clues
You can tell your hydrangeas apart by noticing the flowers and/or foliage.
If the flowers are big, round, and either white or shades of pink, and it blooms early in the season, you have a smooth hydrangea, also called a woodland hydrangea. Botanically it’s known as Hydrangea arborescens. Varieties like ‘Annabelle’, ‘Haas’ Halo’, Incrediball® and Invincibelle® Spirit are among the smooth hydrangeas in today’s market. Smooth hydrangeas never have blue flowers.
When your flowers are football- or cone-shaped, you have either a panicle or oak leaf hydrangea. Flowers start out cream, white or green, and age to shades of pink. No blue flowers ever on either of these two varieties.
Your panicle hydrangea (H. paniculata), which includes such cultivars as ‘Limelight,’ Vanilla Strawberry™, Pinky Winky®, Bobo®, Strawberry Sundae®, etc.) flowers on the wood it will produce in the coming months, i.e. on new wood.
Now you know that new wood flowering hydrangeas (smooth and panicle) are the only ones you should be pruning in spring. All the other flowers on old wood. If you cut the old wood bloomers too early, i.e. any time in spring, you risk losing your flowers.
How Much to Cut
You can take your smooth hydrangeas down to about 18–24 inches (45–60 cm). But don’t go further than that, if even that much. You need strong stems to hold up the flowers, especially after a rainstorm. The older the stems are, the stronger they become so let them be. You can even leave up a few taller stems to form a supporting framework. They will disappear into the plant once it leafs out.
For your panicle hydrangeas, you can cut them down by at least one third. You might want to take even more if the plant has become distorted from snow load and other causes.
Be comforted in knowing it’s very hard to make a mistake when it comes to pruning new wood hydrangeas. They are very forgiving in that they always grow back and fill in.
What About Old Wood Hydrangeas?
These are the ones I call the troublemakers. Old wood hydrangeas come in a few flavors. Some are the ones with the round flowers that you can sometimes change to shades of pink or blue. They can either be mountain hydrangeas (H. serrata) or big leaf hydrangeas (H. macrophylla). Climbing hydrangeas (H. petiolaris) and oak leaf hydrangeas (H. quercifolia) also flower on the growth they produced last year.
If the foliage looks like an oak tree, you have an oak leaf hydrangea. How’s that for an easy identification? You might have ‘Alice’, ‘Snowflake’, or ‘Snow Queen’ among others. The oak leaf hydrangea flowers this year on the growth it put on last year, i.e. on old wood. The flower buds aren’t very hardy, so it likely won’t flower at all in cold climates.
Develop a New Love for “Broccoli”
For all old wood hydrangeas, with the exception of dead, diseased or damaged wood, you must hold off cutting until you see their little buds that look a bit like broccoli. It’s only when those buds emerge that you will know which stems to discard. However, if you need to cut your plant back because it has outgrown its allotted space, then go for it … knowing the potential consequences. A point to remember is that some people in mild climates never cut their old wood hydrangeas and the plants do just fine.
Keep in mind there’s no guarantee of flowers from old wood hydrangeas if your plant has lost its buds to weather or whatever. Many areas had a rapid and deep freeze last November before the hydrangeas had a chance to harden off. That cold spell may have killed the buds that were already formed. If so, you’ll get a nice green bush but no flowers.
And in hardiness zones 5 and below, most old wood hydrangeas (the climbing hydrangea, hardy to zone 4, is an exception) are unlikely to ever flower. They’re just not designed for cold climates. However, you may have some success if you protect the from the winter cold. More information here: Preparing Your Hydrangeas for Winter.
The Magic of Reblooming Hydrangeas
Here’s the saving grace. With a big leaf or mountain hydrangea that reblooms (not possible on oakleaf and climbing hydrangeas), you can still expect to get flowers from that plant even if the terminal buds were destroyed.
Rebloomers have amazing genetics and produce flowers on new stems they will generate in the current season as well as along the stems of last year’s growth. However, these new stems are produced, not from the base of the plant, but from last year’s wood, so you still have to be careful what you prune in early spring.
But you must give them the proper cultural conditions to do that. The right amount of fertilizer (applied in early spring, after snow melt), moisture, and light (part sun) will keep them happy. Then they can concentrate on mid-season flower production.
So you see, this hydrangea pruning thing is really pretty simple. All you need is a sharp pair of pruners to get those new wood bloomers off to a good start.