Warm weather is finally here and the excitement and relaxation of summer is just around the corner. One of the simple pleasures I look forward to every summer is the blooming of my mophead hydrangeas. I have two ‘Nikko Blue’s stuffed and crammed into my very small, overcrowded, front garden. Their thick stems and toothed leaves are already claiming the walkway, and I have to be careful not to knock them as I make the short walk from door to driveway. But they are totally worthy of such prized garden space. Already, I can see the tiny green flower buds forming in the leaf axils, which in the coming six weeks will yield heaping mounds of sky blue flowers.
Photo: Bigleaf Hydrangea with Day Lilies in my summer garden, Commack
If you’re a hydrangea aficionado (like so many gardeners are these days), I’m sure you also feel excitement when you see their tiny green flower buds forming. Or, frustration when you don’t. If you have a mass of hydrangea leaves and no flowers, you might be wondering, what the heck did I do wrong THIS time?! Most likely, the answer is that they were pruned incorrectly (or that the cold killed the tops of them.)
Let me start by saying that hydrangeas are tricky in both pruning and cultural requirements. There have been a handful of times when landscape professionals have called me up asking what the heck they did wrong THIS time to Mrs. Smith’s hydrangeas. The trickiness of pruning hydrangeas begins with the fact that there are so many different types of hydrangeas. You need to know which is which, sometimes down to the cultivar level, in order to prune them correctly…
The four main species of shrub hydrangeas are Smooth Hydrangea (Hydrangea arborescens), Panicle Hydrangea (H. paniculata), Oakleaf Hydrangea (H. quercifolia), and Bigleaf Hydrangea (H. macrophylla). Smooth Hydrangea is actually native to New York, and grows along forested streambanks in its natural habitat. Common cultivars include ‘Annabelle’ and Incrediball™.
Photo: White Dome® Smooth Hydrangea - H. arbroescens, Ithaca
Panicle Hydrangea can be seen on many old homesteads, flowering in late summer. The white flowers fade to a dull mauve as the season wanes. Common cultivars include the old standby PeeGee (‘Grandiflora’), and the newer, quite popular Limelight® and ‘Tardiva.’ Oakleaf Hydrangea, in addition to their big, bright white flower panicles, has oak leaf-shaped leaves which turn a lovely burgundy in the fall. Cultivars include ‘Alice’ and Snow Queen ™.
Photo: Oakleaf Hydrangea - H. quercifolia, Old Westbury Gardens
Bigleaf Hydrangea is by far the most popular hydrangea today. The innumerable cultivars of H. macrophylla are divided into two groups – mopheads and lacecaps. Bigleaf Hydrangea does admirably on Long Island. It is fairly salt-tolerant and can be planted in sandy, acidic soil. It does needs plenty of water though, and some cultivars are not quite cold-hardy during severe winters.
While removing dead flowerheads and dead branches can be done anytime of the year to any species of hydrangea, removal of live branches should be done only at certain times if you want your hydrangea to flower. Both Smooth Hydrangea and Panicle Hydrangea bloom on the current season’s growth. This means that the optimal time to prune live branches without impacting flower production is late winter/ early spring before new growth starts. On the other hand, both Oakleaf Hydrangea and Bigleaf Hydrangea bloom on last season’s wood, which means that flower buds have already been formed in the fall to flower the following spring. Because of this, pruning in late winter/ early spring (the optimal pruning time for many plants) would remove those existing flower buds. New ones would not be formed. Therefore, for Oakleaf and Bigleaf Hydrangeas, pruning live branches should only be done after flowering in August or by mid-September at the very latest.
Now that I’ve made that perfectly clear, let me backtrack and say that there’s one exception. (There’s always an exception in horticulture!) There are a few cultivars of Bigleaf Hydrangea which flower on both old and new wood. This means that if you accidentally prune off the flower buds in late winter/ early spring, no big deal - new ones will form on the new growth. These reblooming hydrangeas are “remontant,” meaning that they flower on both old and new wood. Most outstanding is the Endless Summer® Collection by Bailey Nurseries, Inc. of St. Paul, Minnesota.
Photo: Endless Summer® Mophead Hydrangea - H. macrophylla, Hicks Nurseries
World-renowned plantsman, horticulture ‘God,’ and living plant legand, Michael Dirr, helped discover the original Endless Summer® plant, and led tests of it in his University of Georgia lab, which confirmed its remarkable reblooming ability. In 2004, Endless Summer®, the first tested, truly reliable remontant Bigleaf Hydrangea, exploded on the market. Now seven years later, a couple other reblooming hydrangeas have popped up, and the hydrangea-craze seems to be at an all-time high. These reblooming hydrangeas have simplified the pruning requirements for Bigleaf Hydrangeas. Now, if only we could all figure out how to keep our hydrangeas blue! To be continued!
