Hydrangeas are among the very best of shrubs for late blooming. Not only do they flower when most other shrubs have finished for the season, but they stay in bloom for weeks and even months – and even when dead the flowers of many remain attractive. To get the best from them the first step is to realize that they are not all the same. Those mounds of big leaves, topped with large, round flowers that are often pink or blue are usually called ‘mophead’ hydrangeas, (Hydrangea macrophylla), or if prefer, ‘French’ hydrangeas. Lovely as they are, they are not especially cold-hardy, so if you live in a cold zone the hydrangeas that are easiest for you to grow are panicle hydrangeas (Hydrangea paniculata). These beauties, originally just with white blooms, but today in a much wider color-range, bloom well even in zone 3. This makes them invaluable in colder areas, but they also do well in warm and hot zones, so they can be grown just about anywhere.
To succeed with them – as with all hydrangeas – some attention to pruning is needed. Since panicle hydrangeas need very different treatment to French hydrangeas, let’s look at how to get the best from yours. Maybe you just planted one, and are wondering what comes next. Maybe you have had them for a while, or inherited some in a new garden – and they are a mess. What to do? That’s easy – here we have all the answers, so let’s get started.
What Do You Need to Prune Panicle Hydrangeas?
Don’t worry, pruning panicle hydrangeas is easy, and you don’t need anything special. It is always worth getting yourself a good pair of pruners – what some people call secateurs. There are many different brands – some good, many not – and like everything in life, you get what you pay for. Since a good pair will be your friend for decades, try to buy the best you can. There are two basic kinds. One has a blade with a straight edge that lands on the flat surface of the second blade. These anvil pruners are not so good, because even a small chip in the blade means a ragged cut that can tear the bark – not what you want. The second kind are called bypass pruners. These have a curved blade that slides beside the second blade. Most gardeners find these better. They cut cleaner and they cut bigger branches, so if you are in the market for a new pair – or don’t have a pair yet – then I recommend bypass pruners over anvil every time.
I don’t have any links to benefit from, but I do suggest if you can stretch to it, buying a pair of Felco brand. Available in right and left-hand models, with sizes to fit different hands, these are the professional’s pruner, with replaceable blades, and easy to sharpen and adjust as needed, so you always get the perfect cut.
Hydrangeas have soft stems, so pruners will usually do the job perfectly, and you won’t need anything else. If you have a very large, old bush to do, you might find a pair of bypass long-handle loppers a great help. To round out your gear and make you really to prune anything, a folding pruning saw is the third piece of equipment that is indispensable, although you will only need it on a big old panicle hydrangea. Folding protects the blade from damage, and protects you from accidents when carrying it. Again, invest in something good – Japan makes some great ones, but since they are hard to sharpen – best left to a pro – some gardeners treat them as more throw-away, so you don’t have to overdo it on price – unless you have access to a good, professional sharpener.
When Should I Prune my Panicle Hydrangea?
Since they flower in summer, the time to prune Panicle Hydrangeas is spring. This can be anytime before new shoots start to appear, or when the buds are just opening, or ‘breaking’. If you are a newbie, waiting until the buds show a little green is a good idea, as it will show you exactly what is dead or alive, and where to cut. After a while you will learn that without needing to see buds. It’s important not to cut these plants at any other time, and especially NOT to trim new branches that have leaves on them.
Panicle Hydrangeas flower on ‘new wood’, which is why they are successful in cold areas – flower buds don’t need to go through the winter, with the risk of being killed by cold.
Besides pruning for flowers, we prune all shrubs for shape – and Panicle Hydrangeas are no exception. There are two basic ways you can go with the overall form of your bush. You can keep it low to the ground, with lots of branches coming from the bottom, or you can prune it taller, with just a few (2, 3 or 4) main branches of some length, and then the main growth on the top. Which you choose depends on what you want. Do you have other shrubs in front? Then go for a taller form. Are they in the foreground of a bed? Prune shorter. You get the idea.
[You might also have seen these plants also growing on a thick, single trunk. Called a ‘standard’, you can create this yourself by choosing just one big stem and cutting out the rest, but it is best, of you want this form, to get it ready-made from the pros.]
The cuts you are going to make will be of two kinds. Some will be removing branches completely, cutting them more-or-less flush with the stem they were growing from – don’t leave short stumps that just die and let in diseases. The second will be a cut straight across a young stem directly above a pair of buds. Since the buds of panicle hydrangea come in pairs along the stems, you won’t do any of the sloping cuts you might have learned for pruning roses, for example. Make a clean, flat cut that leaves the buds untouched, but doesn’t leave a piece of stem above those buds. These pairs of buds are what will send out a shoot in spring and early summer, that will end in a cluster of flowers. Young stems are the ones made last year, and you can identify them by their smoother bark, of a lighter shade of brown.
The Really Important Bit
So here is the key thing about pruning panicle hydrangeas. Since they bloom on new wood, how many flower clusters you get depends on how many new shoots there are. But. . .the more shoots there are, the smaller those clusters will be. So the key thing to remember when pruning this shrub is: –
If you leave just a couple of inches of a stem made last year, so there are just 2 or 4 buds, you will have the smallest number of stems and flowers, but those heads will be big, and appear later in the season. These can mean they are more likely to flop and even snap in heavy rain or storms.
If you cut a few inches off a stem made last year, removing just the old flower head back to the first pair of healthy buds, the plants will flower early, with smaller heads, but there will be many of them.
If you cut the stem back to leave 4 or 6 buds, then flowering will be mid-season, with lots of moderate-sized flower heads, less likely to bend over.
You decide what suits you best. Some people love to see really big heads on panicle hydrangeas, but for general landscaping, that ‘middle-cut’ is ideal.
The Steps of Pruning a Young Panicle Hydrangea
New, young bushes need some special attention to develop a strong, permanent framework, making a bush that flowers well every year, and is strong and balanced. The first thing to do is to remove all scrawny stems crowding the plant, leaving just the main stems you want. If you plant is new and young, that could be all you do the first spring – cut back to 3 or 4 strong sticks. It is worth being ruthless the first couple of years – you are laying the groundwork for a good plant, and you won’t regret this at all.
Once you have clean out to leave those main stems, take a look at what is left. If it is all weak and scrawny, remove it, and let the mains stems send out new growth. If it is stronger, then you can build a second level of branches, until, after a few years, you have the framework you want. From then on you can prune the branches from the previous year as mentioned earlier, and you will have a great plant, packed with blooms, every year.