Pruning Hydrangeas
Garden Clippings for August 14, 2021
Gardeners who look to Google for a tutorial on how and when to prune Hydrangeas will be disappointed, because straight answers are hard to find. To make matters simple, the first step in determining pruning details is to determine what kind of Hydrangea you have. Once that’s done, you will know if your Hydrangea blooms on buds formed last year or on new growth formed this year.
Hydrangeas can be divided into 5 categories:
Big Leaf Hydrangeas (macrophyla) blooms in midsummer with large round blooms, mostly in pink or blue. Big Leaf Hydrangeas have thick, heavily textured leaves on plants that are not big. This category of Hydrangea blooms on old wood, but many of the newer Hydrangeas such as Let’s Dance and Endless Summer are rebloomers and will form new buds during the season.
Mountain Hydrangeas, often called Lacecaps, are like Big Leafs, but with clusters of flat flowers with open petals on the outside of the flower cluster. Leaves are broad and thick textured. Like their Big Leaf Cousins, most new varieties of Lacecap Hydrangeas will also form buds and flowers during the current season.
Smooth Hydrangeas bear the showy white round flowers that are true showstoppers. The most common are the old fashioned ‘Annabelle’ and the newer ‘Incrediball’ with larger flowers. This category blooms on buds that have formed on new wood in spring, and open in summer.
Panicle Hydrangeas are easy to recognize because their blooms are cone shaped. Most varieties have blooms that open in pure white, then turn shades of pink followed by red tones. Panicle’s leaves are smaller, but the plant is usually bigger. Popular varieties include ‘Limelight’, ‘Pinky Winky’ and ‘Little Lime.’ Tree form Hydrangeas fall in this category.
Oakleaf Hydrangeas are easy to distinguish because their leaves are shaped like Oak Leaves. Flowers are less abundant in favour of more interesting leaves that often turn bronze in fall. Oak Leaf Hydrangeas bloom on buds formed in the previous summer.
Hydrangeas that bloom on old wood should be pruned immediately after they are done flowering. But if you prune these in September when flowers are almost spent, there won’t be enough time to form buds in preparation for next year. By pruning these Hydrangeas, you might forfeit flowers for one year. The recommendation is to avoid pruning these Hydrangeas unless you find the plant to be too big. But go ahead and do minor pruning each spring to remove old stems that are weak, dead or not performing.
Hydrangeas that bloom on new wood can be pruned in late fall or early in spring. These include Panicle and Smooth Hydrangeas. Tree form Hydrangeas should be pruned back each spring to avoid the top becoming too heavy.
Hydrangeas that are repeat bloomers should be pruned lightly, to avoid removing future blooms. Use a hand-held secateur type pruner to remove the oldest tired stems that are weak, dead or not performing.
Climbing Hydrangeas, a category not mentioned above, blooms white on attractive vines that lean or climb on fences and walls. These shade tolerant Hydrangeas won’t need pruning unless to make the plant smaller.
The good news is that with the exception of tree form varieties, Hydrangeas do not need much pruning. That’s in contrast to flowering shrubs like Forsythia, Spirea, Snowball and Weigela that are reinvigorated after they are cut back. Unless your Hydrangea has become too large, it might be best to leave your pruner in the garden shed.
