(Feature photo is courtesy of Ginger)
Learning how to prune hydrangea is one of the top ways to get the most out of your shrubs. But did you know that different types of hydrangea plants have different pruning requirements? And that improper pruning can literally mean a bloomless season (or worse)? But don’t worry, because we’re here to tell you everything you need to know to keep your hydrangea in tip top shape.
First things first: How to Identify Your Hydrangea
If you already know what you have, then you can skip this part! But if you still need to sort out exactly what type of hydrangea you have, this section is required reading.
There are four common types of hydrangea: Mopheads/Lacecaps, Oakleaf, Snowball, and Paniculata.
The leaf stems are the biggest clue to your hydrangea’s identity, especially when combined with the type of flower it produces.
Mopheads & Lacecaps (macrophylla) Hydrangea
The leaf stems (petioles) on a mophead or lacecap will be short, meaning that the leaves hug the main stem.The leaves on this type are usually heart-shaped or ovoid with serrated edges. They’re about 4 to 6 inches long and 3 to 5 inches wide, though some varieties will be larger. The leaves are also somewhat thick and semi-shiny.
On a mophead hydrangea, the blossoms grow in round and oval mounds of tightly clumped individual flowers. On the lacecap varieties, the flower head shape is almost the same, but you will have itty-bitty, lacy-looking flowerbuds in the middle, surrounded by larger, fully developed flowers. The buds are the fertile flowers, while the full blossoms around the edges are infertile.
Though considered one group when it comes to their pruning requirements, each of these look quite different when in bloom. It is also interesting to note that mopheads are the ONLY hyrdrangea that has colored blossoms when they first open. All other species will be white, so that may be the first hint that you don’t have a mophead, unless you have a white mophead cultivar, which is uncommon.
Oakleaf have leaves that have the same shape as the leaves on a red oak. The size of the leaves can range from 4 inches to 10 inches long and just as wide, and they will often stay on the plant most of the winter. They are not really considered an evergreen though because after several freezes they are not very attractive. They also have cones of flowers, as opposed to mounds or balls of flowers and ALL oakleaf hydrangeas will bloom white before changing color. It should be very easy to identify this species if you have it. (Photo is courtesy of RPOP).
Snowball (H. arborescens) Hydrangea
Snowball are hands down the most common type of hydrangea. They might remind you of lollipops. The flower heads are usually very large, but made up of tiny, individual blossoms. The leaves are usually thinner, and oftentimes heart shaped. But somewhat like the macrophylla. They also tend to be a bit floppier than the ones on mopheads and are not shiny, but have a matte finish. The leaf stems (petioles) are also long, holding the leaves further out from the main stem.
The one single trait that sets this species apart is that the blossoms will start green, turn white for two or three weeks and then turn green again, which is when you can dry them. These humongous blossoms also tend to fall over in high wind and heavy rain. So you might want to plant them on the side of the house with the least wind, as long as it is not in complete shade.
PG (paniculata) Hydrangea
The leaves on paniculata plants are normally smaller than other hydrangeas. They are also thinner and can either be finely or coarsely toothed. They have a rougher overall texture and are medium-green with a matte finish. The biggest identifying characteristic is that the leaves grow in a threesome from one stem node and are spaced around the node, in a whorl.
This type of hydrangea can be pruned to grow in both a tree and shrub form and is not easy to identify by the type of flower heads. They can be cone-shaped or round, full or sparse, stand erect or droop. In fact, the name paniculata comes from the panicle-type flower head they have. Like the oakleaf, these ones will start as white, and turn pink as they age.
These hydrangeas can grow to lofty heights of 8 to 10 feet and sometimes taller, matching their height in breadth. Photo courtesy of Alan Buckingham.
How to Prune Hydrangea
Now that you’ve identified your hydrangea(s), we can talk about how to prune hydrangea to keep it healthy and beautiful. Please note that pruning and deadheading are two different things. Deadheading means removing the old blossoms as they fade, while pruning changes the total appearance and form of the plant.
There are two methods for pruning:
Hydrangea Pruning: Method 1
This method for how to prune hydrangea is for mopheads, lacecaps and for oakleaf hydrangeas. These hydrangeas bloom on old wood which means they develop buds on stems that have been on the plant since the summer before the current season. They develop these buds sometime between August and October for the following summer’s blossoms. Therefore, if you remove these stems in the late fall, winter, or spring, the flower-producing buds are also gone. Which means NO FLOWERS (or only a very few) this summer. So it pays to use prudence and patience when pruning mopheads, lacecaps or oakleaf hydrangeas.
Top 3 Tips for Pruning Hydrangeas
- You can remove dead stems at anytime throughout the year (and you should do it every year.)
- Once your plant is at least 5 years old, remove about 1/3 of the older, living stems, cutting them down to the ground in late June through early August. Try to choose ones not already blooming or that are starting to look a bit naked. Keep an eye to how this will change the shape of the current plant, stepping back once in a while to see how it’s looking. Doing this will revitalize the plant.
- To reduce the size of a plant, cut it back in June or July without doing away with the following year’s blossoms. It won’t take long for it to return to its original size, which is why planting where it doesn’t need pruning is the best route.
Hydrangea Pruning: Method 2
Use this method for the snowball (H. arborescens) and PG (PeeGee or H. paniculata) type of hydrangeas. Both of these hydrangeas bloom on new wood, which means that you can prune them anytime, except in the spring when they are setting buds, or in the summer when they are either preparing to bloom or are in full bloom.
Some people even grow hedges of the snowball type. They prune them back almost to the ground in the fall, so as to present a neater winter appearance. Just be aware that this type of drastic pruning can keep the stems from reaching the sturdiest size to adequately support the huge flower heads. If you do this, you may have to stake your flowers in the spring and summer, or grow them along a fence and use string across the front to offer support when in full bloom.
How Often to Prune PG Hydrangea
When pruning PGs, we don’t recommend pruning every year. Just trim out criss-crossing branches or those that detract from the overall form. The developing trunk and the top branches should not be removed and you should also not attempt to make it look like the tree the first year or two. Patience is key here. Each year just trim a few of the lower branches in order to expose the developing trunk, and then let nature take its natural course.
One note: if a tree-pruned paniculata’s main trunk breaks close to the ground, it will grow back as a shrub unless the training process starts again from the new shoots.
Don’t Want to Prune? Go for Everbloomers
Though this may seem like a lot of work, it really isn’t. Once you have the knowledge, the rest is easy. But if you’d rather not worry about it there are a small group of mopheads that will bloom regardless of when they are pruned. These are called everbloomers and will bloom on both old and new wood.
How Hydrangeas Change Color
Want to amend your soil to change the color of your mopheads? It’s simple. The trick to getting these hydrangea to change color lies in the soil pH. Hi-Yield Agricultural Limestone will reduce the pH of your soil relatively quickly, resulting in blue coloration. Hi-Yield Aluminum Sulphate will increase the pH, giving you pink.
You also might want to invest in an inexpensive soil tester to determine where your pH lies right now. Especially if you are planting new mophead hydrangeas and want to be sure of a particular flower color.
We hope that this has provided some valuable information, as this is one of the questions that our Master Gardener sees on a regular basis. And if you still have questions about how to prune hydrangea after reading this, please drop us an email. Our goal is to help you to be the best gardener you can be!