How to Prune Panicle Hydrangeas
By Debbie Lonnee, originally appeared in Northern Gardener Magazine
With their diverse habits, flowers and incredible color, the genus Hydrangea has become the country’s most popular shrub. Most Minnesota gardens now have at least one species represented, and sometimes gardeners are confused as to how to prune their hydrangeas.
Hydrangea paniculata, commonly known as the panicle hydrangea, is widely used throughout the state. In recent years, breeders have greatly improved the species, and we now have many cultivars to choose from, some with a large mature size, and more recent dwarf forms for smaller gardens.
Panicle hydrangea brings us flowers in mid to late summer, giving us a blast of color in July, August and September.
Pruning these beauties is as easy as choosing a beautiful early spring day to get out the pruning shears. We call this ‘dormant’ pruning, getting this job done BEFORE the plant leafs out in the spring. I typically prune sometime in March or early April, usually once the snow has melted and access to the plant is easy.
One of the advantages of dormant pruning is that the plant, with no leaves, is easy to study. You can stand back and take a look at height, spread, shape, form and decide where to make your cuts.
Step 1: This is a mature Vanilla Strawberry® panicle hydrangea. It typically matures around 7-8’ in height. Every year I prune this plant back approximately 30-50% with no adverse affects to the shrub. This photo is from spring 2014, when snow melt was late. I didn’t get to pruning it until the leaf buds had opened about ½”. You can do it earlier (when it is completely dormant), before any leaf bud swelling starts.
Step 2: I use a Felco hand pruners to make my cuts. I start making my cuts from the outside branches, working my way around the shrub. I try to shape the shrub as I go. Step back from the shrub now and again to observe your work and make sure you are creating the shape you are looking for. I try to have a rounded shape when finished with panicle hydrangea, which is not always easy as this plant has a very upright growth habit.
Step 3: If you are pruning with new buds showing, you can make your cuts just above the buds, about ¼”, on an angle. If they are not showing yet, don’t worry about placement of your cut, the nearest bud below your cut will open and this will not damage the plant.
Step 4: Here is the finished shrub, all cut back. It seems a bit radical to be taking so much off of the plant (and I do not recommend this method for all other shrub species), but this works for panicle hydrangea. This heavy pruning will promote heavy, thick stems which will hold up the very large flowers. One of the biggest complaints about panicle hydrangea is that the flowers are ‘floppy’ in late summer. Prune like this and you will avoid that problem.
Step 5: This photo was taken July 8th and you can see the new growth standing straight and tall. If you look closely, you will see the new flower buds forming at the terminal ends of the shoots. Please note the beautiful red stems of this newer cultivar.
Step 6: On August 22, it is in full bloom and the flowers are upright and erect! Vanilla Strawberry starts with a beautiful white flower which then starts to turn pink at the bottom of the flower panicle and the color slowly moves its way up the panicle, ultimately turning a strawberry red. Cooler nighttime temperatures in August and September will result in the best flower color. Fall of 2015 had just the right conditions for beautiful flower colors.
Step 7: This cell phone picture was taken on October 4th, and the red color had been spectacular all throughout September and into October. By this time a few flowers are flopping, but I will blame that on a couple of late season wind storms that really battered the yard.
These simple and easy pruning techniques can be used on all panicle hydrangea cultivars. Even newer, dwarf varieties, such as Little Lime® and Strawberry Sundae®, which mature in the 4’ height range, can be cut as much as 35-50% in the spring to keep them shapely and with stiff stems that hold up the more petite flowers. So get out and enjoy the early spring weather and get some pruning done!