Time to Prune Some Hydrangeas, IF NEEDED

The Reason:
I noticed my Hydrangea macrophylla (mopheads and lacecaps) are getting leggy, over-grown for the space and the flowers are fading into their seed production stage. You should have a reason to prune any plant and not because the neighbors are doing it or you have some new pruning shears or a hedge trimmer. I am a lazy gardener so this is not a problem for me but I do have other family members and friends that are of the antsy variety, type A, hyper-gardener category that have an uncontrollable need to DO. If you identify a legitimate need, then you have a reason to prune and this is the time to prune some hydrangeas.

The Need:
I often wonder how plants survived without the help of well-meaning gardeners. Actually, they managed for thousands of years making do on nature’s sustainable bounty. I guess our meddling with nature and our habit of removing plants from their native habitats and moving them all over the world gave some reason for manipulation to provide microclimates for survival in hostile areas. Gardeners (I am guilty) want to enjoy and feed our insatiable desire to collect, improve and have all things beautiful in our ready reach. There is no life-sustaining requirement to prune a hydrangea. The needs are for size control or aesthetics. If the plant has outgrown its space, has become leggy, diseased, frost damaged or has other die back issues, then pruning is legitimate.

The Time:
For mopheads and lacecaps (Hydrangea macrophylla), prune now and not too much past mid August in Alabama. Also included in this pruning group is Alabama’s official State native plant, Hydrangea quercifolia or oakleaf hydrangea.

Hydrangea quercifolia - oakleaf hydrangea

A study done at Auburn University a number of years ago looked at pruning this species of hydrangea every month of the year to see if the plant still bloomed the following season. Most mophead hydrangeas were reported to set their flower buds for the next season on old or previous season’s growth at the terminal bud. So if you pruned in the spring, you cut off some or all of the flower buds. Research showed pruning in mid-September still yielded flowers the next season but to be safe and have a better formed plant, prune no later than late July to mid-August. Another reason not to prune into late summer and early fall in Alabama is the potential for delaying dormancy and forcing new growth before an early freeze hits our area which can produce UGLY i.e.… black, dead leaves and stems and possibly a dead plant. Pruning now in early July at the end of bloom time for most of the Hydrangea macrophylla cultivars is the best time to look for a need to prune. As with most things in nature, there are some exceptions. There are cultivars that set buds on old and new wood, and on the lateral as well as the terminal buds and offer the trait of remontant blooming or a re-blooming. Some of these cultivars include: All Summer Beauty, Nikko Blue, Penny Mac, Endless Summer, Blushing Bride, David Ramsey, Decatur Blue, Mini Penny, Oak Hill and Madame Emily Moulliere. These you can whack at anytime, if necessary, and terminal and lateral flower buds form and keep giving.

Other hydrangea species like PeeGee or panicled hydrangea (Hydrangea paniculata)

Hydrangea paniculata - panicled hydrangea

or our native, Smooth hydrangea (Hydrangea arborescens)

Hydrangea arborescens - Smooth hydrangea

are pruned in early spring because they bloom on the current season’s wood. If you feel the need, these plants could be cut to about 4 inches from the ground in early spring and will produce new shoots and blooms during the season.

What and How to Prune?
Dead, dying, diseased stems and flowers can be removed at any time. Cut past the dead tissue and take away from the plant area to avoid leaving any of the insects or diseased tissue behind to infect/infest the rest of the plant.

Flowers are more prolific on newer wood so after the plant reaches 4 or 5 years of age, the process of “thinning” is a nice technique. To thin, find older, larger, thicker canes and prune them at the base of the stem. Remove about 1/3 of these older branches. After 3 years of this process, you have completely renewed the plant. This is an option but not required.

Deadheading can be another reason for pruning.

Some people like to remove the old flowers for drying and using in arrangements. Another reason is that flowers are a “sink” or drain on energy that could be used elsewhere on the plant for additional growth. When plants, like people, reach the sexual phase of life and their focus and purpose is procreation and survival of the species then all energy is diverted to that most important function. If you remove the flowers or sexual parts of the plant, the energy going to that venture is redistributed to other neglected areas. There is no need to prune for the health of the plant but the reason is to increase vegetative growth. This is sometimes done in nurseries when plants are not for sale that year. They get a larger, fuller plant for the customer by removing the flower buds.

Also, like people, plants often become old, overgrown, and unshapely and have a reason for a little nip and tuck or major reduction for aesthetic purposes. Now is the time for this major pruning without losing flowers. In commercial nurseries, time and money do not allow for targeted cuts at 1/4 inch above the bud, at a 45 degree angle

and to the leeward side of the bud, as is often described in pruning texts. If a good lawn mower is not available for the task, nursery workers hug the plant and scrunch it up into a bouquet like a dozen roses ready to be stuffed into a small vase, then 1/3 to 1/2 of the stems are cut at the same level and released.

When the stems settle, a rounded, well-shaped but scalped looking plant remains. This time of the year, new buds will break at the nodes and quickly cover the unsightly cuts.

There is the possibility of disease if all conditions are right for inoculation and growth of a pathogenic fungi but this does not often happen. The other option is to selectively pick out the long, overgrown stems, move down the stem inside the canopy of the shrub and cut at 1/4 inch above the bud at a 45-degree angle on the leeward side of the bud. This is for the perfectionist and for those who have a need to DO. Please note that if there is a long “wild hair” shoot that has a mind of its own, do not be kind and nip back a little.

Cut it hard, back to within the canopy or to the ground. When pruned, new buds arise just below or 4 to 6 inches below the cut. If you prune just the tip and think you will encourage branching back down to the rest of the plant, it will not happen. You will have a wild hair with witches broom at the tip. Tough love is needed here to bring the unruly branch back into bounds.

That is a lot to say in Hort Shorts about a gardening job that you don’t NEED to do. Nature managed to be happy with the product before we became the surrogate gardeners. However, if you have the urge and have a reason to justify your need to prune, this is what science and gardening piddlers have discovered over time.

On a general Hydrangea note, if you have not collected a number of species and cultivars of hydrangeas and do not have them scattered in all corners of your yard and in containers on your patio, you are missing one of nature’s greatest gifts to her surrogate caretakers. Plant, Share and Enjoy a Hydrangea!

For more information on hydrangea:
Auburn University Hydrangea Trials

Please come back often and enjoy HortShorts as much as I enjoy posting them for you. Your enthusiastic plant response is always encouraged and welcome.