How to Prune Hydrangeas
If you've ever wondered if you could achieve a glorious display in your garden, this book is for you. These days there is a variety of hydrangea for every garden, no matter how hot or cold, sunny or shady.
I've been growing hydrangeas for over 20 years, but I have to admit, I've never pruned one. My new garden, in New Hampshire, has some lovely sunny flower beds and a large collection of hydrangeas, so to be sure I get things right, I've been researching them in a general way. In passing I found that some hydrangeas, not all, are supposed to be pruned.
What type of Hydrangea Do You Have?
Hydrangeas come in several different forms and some need to be treated differently, so the first step in deciding how to look after your hydrangeas is to work out what type of hydrangea you have.
Most blue, pink or purple hydrangeas are lacecaps or mopheads. Hydrangeas with white flowers aren't so easy to categorize. The best way to tell them apart is to look at their leaves.
Hydrangea Paniculata, sometimes known as Pannicle Hydrangeas have small rough leaves. They grow in threes and are around 3-6 inches in size. The blooms are often, but not always, cone shaped and the plant can become a tree. (8-10 feet high and just as wide) If your hydrangea is extremely large, and especially if the blooms are white at first, it is most likely hydangea panniculata, but do check the leaves. Some forms have round blossoms and are quite small. These fabulous plants can be grown almost anywhere. In the USA they are hardy even in zone 3.
This type of hydrangea only blooms on new stems. You can prune them at almost anytime, though it's not a good idea to prune them when they're about to bloom. Some people who find hydrangeas 'messy' in winter, prune them right back to the ground and they will still bloom freely the following year. Personally I enjoy the hydrangea heads in my garden in winter. As I write this, they are glistening with frost, as though I'd gone outside and sprayed them with glitter.
Another type of hydrangea is hydrangea quercifolia, the oakleaved hydrangea. If you have this type of hydrangea in your garden you'll have noticed the leaves, shaped like an oak tree's, change color in the autumn. Like pannicle hydrangeas, the flowers will open white and often turn pink as they get older. If you have really dry conditions in your garden, then this is the ideal hydrangea for you. Prune these plants before August. They flower on old wood, so if you remove too much you'll remove all the potential for flowers and see no blooms.
Climbing hydrangeas, hydrangea pettiolaris, require no pruning until they reach a point where you want to cut them back. The are pretty slow to get started, but can reach over 50 feet tall. These are among my favorite plants as I always seem to end up with north facing gardens, or gardens with a lot of shade. These hydrangeas are almost the only flowering vine to grow well in shady corners, where the deep green leaves and white flowers will brighten the darkest, dreariest of walls.
For most people the word hydrangea brings to mind large blue flowers. Blue and violet flowers are always found on hydrangea macrophylla, the mopheads and lacecaps which brighten so many late summer gardens. Their leaves are usually heart shaped and can be shiny. Though mopeheads and lacecaps have different flower forms, their leaves are identical, like their pruning requirements. If you are happy with the size and shape of your hydrangea macrophylla, don't feel you have to prune it all. If you do want to change the shape, treat it just like the oak leafed hydrangea as it produces flowers on old wood.
The last type of hydrangea is hydrangea arborescens. The leaves are very similar to those of the mopheads, but with a rougher texture which is not so shiny. The leaves are carried on long stems and stand further from the main stem of the plant. Many of these plants have wonderful huge round white blooms, though there is now at least one pink variety, 'Invincibelle Spirit'. These hydrangeas, like the pannicle hydrangeas, produce flowers on new wood and can be pruned at almost any time, even quite harshly. 'Annabelle' is one of the most famous varieties, it has been known ti survive extremely harsh winters without any damage and can be pruned harshly, but beware. Although your plant will still bloom the following year, the stems may not have been had the time to grow strong. The blooms are very heavy, and the result can be that the whole bush is flattened by a simple rain storm. If this is a serious problem you can support you hydrangea with some lattice work trellis to take the weight of the large blooms.