By: Sandy Feather ©2007
Penn State Extension
Q. I have many hydrangeas in my yard, ranging from pink to blue. They did not have many blooms last year. Since they are in several different gardens, it should not have been the soil. Is there anything I can add this spring to help them bloom? I did not remove the "old wood" because I have heard they will not bloom if you cut the stems.
A. Unfortunately, if our short, but severe winter has damaged the flower buds there is nothing you can do after the fact. Bigleaf hydrangeas (Hydrangea macrophylla) are perfectly hardy in our climate, but their flower buds are not. That is why you often get a lot of foliage and no flowers on this type of hydrangea. They "bloom on old wood." That means bigleaf hydrangeas set their flower buds during the previous growing season.
If those buds are damaged by cold weather, or removed by pruning at the wrong time of year or by deer browsing, you will have few, if any, flowers the following summer. They are best pruned as soon as the flowers begin to fade, because new flower buds are formed soon after they finish flowering. Unless the plant is outgrowing its space, there really is no need to prune bigleaf hydrangeas annually.
The best approach is to periodically remove the largest, oldest canes at the soil level to encourage new stems to sucker up from the base. This type of renewal pruning will result in larger blooms without giving your hydrangeas that sheared look. The added benefit of pruning this way is that even if you prune at the wrong time of year, you will not be removing all of the flowers, just those atop the stems you cut out.
You may actually get a few flowers later in the summer because some bigleaf hydrangeas have the ability to bloom on old and new wood. The term "bloom new wood" refers to plants that bloom on the current season's growth. Plant breeders are exploiting this trait to come up with new macrophylla varieties that bloom more reliably in colder climates. A good example is the popular recent introduction called Endless Summer®.
New cultivars with this characteristic are in the pipeline and will become available as they prove their garden worthiness. They are understandably popular with gardeners in colder climates. After all, who doesn't love those long-lasting pink or blue flowers?
There are other varieties of hydrangeas that bloom more reliably in our climate. These include saw-tooth hydrangeas (Hydrangea serrata). Although they bloom on old wood, they are native to the mountains of Japan and Korea, and are better adapted to colder climates such as ours. Like bigleaf hydrangeas, their blue or pink flowers can be lacecap-type or mophead-type, depending on the cultivar. Our native smooth hydrangea (Hydrangea arborescens) blooms on new wood, so it grows very well here.
Popular cultivars include 'Annabelle' and 'Dardom' (White Dome®). Peegee hydrangeas (Hydrangea paniculata) are old-fashioned favorites, frequently grown as small trees. They bloom reliably on new wood, and the plants are long-lived.
Excellent cultivars of peegee hydrangea include 'Tardiva,' 'Pink Diamond,' and 'Bulk' (Quick Fire). Last, but far from least, is oakleaf hydrangea (Hydrangea quercifolia). Native to the southeastern United States, oakleaf hydrangeas also bloom on old wood, but their flower buds are hardier. Good cultivars include the compact 'PeeWee,' the double flowered 'Snowflake,' and 'Snow Queen.'
Now if we could just breed hydrangeas that taste awful to Bambi!