It is unavoidable. Warmer days, birdsong, snow melt and crocus blooming can only mean one thing. It’s time to get out the scissors and do some pruning.
However, in the case of hydrangeas, improper pruning is the main cause of the lack of flowering. This is because many gardeners prune them at the wrong time. So let’s clarify when to prune a hydrangea once and for all.
When to prune a hydrangea: If it blooms on new wood …
The ones you can prune in early spring are the species that bloom on stems that will produce in the current year, that is to say, in new wood. But then you have to know what hydrangeas they are. So let’s dig a little deeper to understand it.
You can distinguish the different hydrangeas by taking a look at the flowers.
If the inflorescence is large, round or domed, white or pink, and blooms early in the season, you have an arboreal hydrangea (Hydrangea arborescens). Varieties such as ‘Annabelle’, ‘Haas’s Halo’, Incrediball® and Invincibelle® Spirit are some of the arboreal hydrangeas currently on the market.
Note that the arboreal hydrangea never produces blue flowers.
Hydrangea arborescens’ Haas’ Halo ‘
Hydrangea arborescens ‘Annabelle’
Hydrangea arborescens Invincibelle® Spirit
If the flowers are cone-shaped, you have a paniculata hydrangea or, more rarely, an oakleaf hydrangea. The flowers start off as cream, white, or green and age to shades of pink.
No blue flowers appear in any of these varieties.
Hydrangea paniculata Strawberry Sundae®
Your paniculate hydrangea (H. paniculata), which includes several cultivars such as ‘Limelight’, Vanilla Strawberry ™, Pinky Winky®, Bobo® and Strawberry Sundae®, will flourish on the wood it produces in spring, that is, on new wood.
The arboreal hydrangea and the hortensia paniculata are the only hydrangeas you should prune in spring. All the others bloom on old wood (wood from the previous year).
If you prune the species that bloom on old wood any time in the spring, you risk losing the flowers of the year.
How much to cut
Once you’ve identified when to prune a hydrangea, you want to be sure of how far you should cut. You can cut a arboreal hydrangea up to about 45-60 cm high, but do not go further. You need strong stems to support the flowers, especially after a storm. The older the stems, the stronger they are, so leave them. You can even leave some taller stems to form a kind of support frame for the other branches. These older branches will not be seen once the bush begins to grow again.
Consider trimming your panicle hydrangeas by at least one third. You can prune even shorter if the plant has been deformed by snow load or other causes.
Fortunately, it is very hard to go wrong when it comes to pruning hydrangeas that bloom on the wood of the year. They are very forgiving and grow back quickly after pruning, creating a full look in just a few weeks.
What about hydrangeas blooming from old wood?
These are the so-called “problematic” and the question of “when to prune a hydrangea” is a better gift. When we go wrong with pruning, it is always with these varieties.
The hydrangeas blooming on old wood they are of various species. Among them, the most used are:
The best known are the “hydrangeas” that produce round balls of blue or pink flowers. They can be the serrated hydrangea (H. serrata) or the large leaf hydrangea (H. macrophylla), known as blue hydrangea in Canada.
The large-leaved hydrangea is the most popular, but the two species are very similar and do not need to be distinguished.
The other two common species that flourish on old wood are the climbing hydrangea (H. petiolaris), which is easily distinguished from the others by its climbing stems that cling to walls, fences, and logs, and the oakleaf hydrangea ( H. quercifolia), identifiable by its foliage that looks like … oak leaves! It’s easy, right?
For more safety: Look for the “broccoli” 😂
In the case of hydrangeas that bloom on old wood, no need to prune in springexcept to remove dead, diseased or damaged branches. Otherwise, you can’t until you see her little green flower buds that look a bit like broccoli. This way you can easily see which stems will bloom and you can trim, if you wish, those that will not.
However, if you need to reduce the size of your plant (because it is exceeding the allotted space, for example), yes, you can prune in early spring, but keep in mind that this will eliminate the flowering of the current year.
Keep in mind that some gardeners in moderate climates never prune their old hydrangeas and the plants continue to thrive.
About Low hardiness (little resistance to extreme cold)
Please note that hydrangeas that bloom on old wood, except climbing hydrangea, they are not very resistant. Therefore, keep in mind that there is no guarantee of flowering if the plant has suffered the elements or other damages. For instance, an early fall frost can kill flower buds that are already present on the stem but are not visible. If so, you will get a nice green bush, but no flowers.
This is less of a problem in Europe, where winters are rarely severe, and even less so in the even milder coastal regions, where hydrangeas grow almost to giants. However, it is a major problem for Canadian gardeners. There, both hydrangeas and oakleaf hydrangeas rarely bloom more than sporadically … unless you protect them from the winter cold. To know how to do it, read Growing blue hydrangeas in cold weather.
The magic of remontant hydrangeas
However, within the two hydrangeas (the toothed and the large leaf), there are remontant varieties, that is, those that have the ability to produce a second flowering from secondary buds located lower on the stem, although the terminal bud has been destroyed.
Among them are cultivars such as Endless Summer®, ‘Penny Mac’ and Twist-n-Shout®.
If conditions are right, the secondary shoots will start to grow and produce flowers about a month after the first bloom. They should not be pruned in springexcept to remove dead ends, as your new flower stalks continue to grow from the old wood.
But this second flowering is not guaranteed. You must take good care of the remontant hydrangeas.
A good one fertilization (applied in early spring, after the snow has melted), a well drained soil but slightly damp and a reasonable light intensity (between half shade and full sun). Under these conditions, at least if the stems from the previous year have not frozen to the ground, as is often the case in countries with climates such as Canada, remontant hydrangeas can focus on producing a second bloom in the middle of the season.
As you see, knowing when to prune a hydrangea is really easy. All you need is a sharp pair of pruning shears and a good idea of the species you have in your garden. This way you can prune hydrangeas to the perfect size without sacrificing the flowers.
Do you want to know more about hydrangeas? Take a look at these posts:
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