If you gathered in one large room, all the plant pros from all over the world and asked them to name the number one question they are asked by customers, that normally diverse and typically quite contrarian group would find themselves in unanimous and surprising agreement. Questions related to how to prune a hydrangea, why one either does or does not flower from one year to the next, could fuel a reality TV show … maybe even to rival “Game of Thrones.”
Here are three reasons why you hydrangea may not be blooming:
Hydrangea not blooming?
Improperly Timed Pruning: By far the most common reason for some hydrangeas to not flower is pruning at the wrong time of year. Hydrangeas come in a variety of types. Some set their flower buds in the fall for the following spring. If you prune that type in winter, there won’t be many/any left to flower in spring. This is the case for the popular bigleaf hydrangea (Hydrangea macrophylla,) the type that typically has glossy, bright green leaves and either pink or blue flowers in summer. The always popular oakleaf hydrangea (H. quercifolia) falls into this same category of old wood bloomers.
(Note: a few of the newer varieties of H. macrophylla actually produce flowers both on last year’s growth and current season’s growth so will bloom in spring even if you prune them hard in winter, but all flower better if you skip the winter prune.)
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Hydrangeas that flower on the current season’s growth (sometimes called new wood flowering) can be cut all the way to the ground in winter and they will still bloom the following spring after the new growth is produced. The native smooth hydrangea (H. arborescens) and the panicle/tree hydrangea (H. paniculata) both fall into this category.
Winter/Cold Damage: Some hydrangea species can handle a whole lot of cold without even the least of a shiver. When I lived in Bangor, Maine it took no time at all to see that both the smooth hydrangea and panicle hydrangea were (and still are) staples in the landscape. They can handle cold.
Big leaf hydrangeas, on the other hand, are best considered snowbirds. They can handle some winter cold but what they don’t like is the up and down temperatures of a continental climate. A few warm February days during winter can cause a bit of a false start for big leaf hydrangeas. And once those buds (that contain the flower initials formed last fall) start to swell even a bit, any temperature below freezing will result in a total or partial loss of flowers for the coming season and will leave you with a big green bush with no flowers. If the cold is borderline, sometimes you’ll just get a few flowers near the ground where they were either protected from the freeze by snow cover or from a bit of warmth radiated up from the ground beneath.
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Too Much Shade: Many of us who start off with a sun garden know that it won’t often last very long. Trees grow. Other large shrubs grow. Over time, a once floriferous hydrangea can lose its flower power as maturing plants in the vicinity start to suck up the essential sunlight. All hydrangeas are quite shade tolerant — meaning they can survive quite nicely in even a moderate amount of shade. But as the amount of incident light decreases, so does the flower production. The solution is to move your hydrangea to a sunnier spot or open up the tree canopy with some strategic tree pruning.
There is also a short list of other reasons for a gradual decrease of hydrangea flowers. Of course the ever-present white tailed deer that so many of us battle in our gardens can chow down on your hydrangeas, meaning no buds make it to flowering stage. Poor mineral nutrition, moisture stress, and a host of other cultural insults can keep hydrangeas from flowering but those are minority cases.
When to prune hydrangeas for best blooms
First things first. Like most plants, hydrangeas do not need to be pruned. If left unpruned, they will be just fine. After flowering, some people like to remove the old blooms (which is completely fine) while others like to leave them in place for little winter texture. But in both the old wood and new wood blooming hydrangea species, no pruning is necessary. If you just let them do their thing, they’ll do their thing.
Old Wood Bloomers: If big leaf hydrangeas are pruned at the wrong time of year, they won’t flower the next year. But that doesn’t mean you can’t prune and still have flowers. If you want to prune to encourage tighter branching or maintain a slightly smaller plant, prune as soon as the current crop of blooms start to fade. The goal is to encourage lower buds to break and produce new shoot growth before the end of the growing season, with enough time for a new crop of flower buds to form. A thorough watering regime post pruning will help make sure that new growth forms. My general rule of thumb is to do this kind of pruning before the middle of July.
Other than the bigleaf hydrangea, oakleaf hydrangea (H. quercifolia) and the less common climbing hydrangea (H. petiolaris) fall into the same group of old wood bloomers.
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New Wood Bloomers: These are far less fussy. If you wantm you can clean them up by removing the spent flower heads about any time of the year. Whole plants (young or old) can be cut to the ground in winter (which will create a plant with fewer but larger blooms), or they can be left to their own devices with no pruning. The no pruning approach will generally produce a plant with a greater quantity of smaller blooms.
Worldwide there are somewhere around 80 or so species. Most are shrubs. Some approach tree status. A few are climbing vines. And if you’re lucky enough to have a specimen or two of the rarer species in your garden, all you need to know to determine the best pruning time is whether it blooms on new or old wood.
But then if you do have some of those plant geek species in your garden, you’re probably already getting the pruning question from your friends and neighbors. Maybe you need your very own television series.
Paul Cappiello is the executive director at Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.
This article originally appeared on Louisville Courier Journal: Reasons your hydrangea won’t bloom and how to fix it
