As we get closer to spring, our horticulture team will be performing two of the most important winter-garden tasks: rejuvenation pruning and perennial cutbacks. A great deal of the plants in the Park are woody perennials—plants that survive the winter by producing wood. In response to increasing nighttime and decreasing temperatures, these plants go dormant, shutting down many processes and essentially hibernating until spring returns. As it so happens, this dormant period is the perfect time to prune plants, allowing us to remove any unwanted branches, as well as give the plants some shape.
We prune during winter for two principle reasons: during the growing season, plants respond to pruning by producing more stems where they were cut, and certain plants have a tendency to “bleed,” leaking a large amount of sap when pruned outside of dormancy. Aside from regular pruning, we also practice rejuvenation pruning on certain shrubs and small trees. As some plants mature and their wood grows older, they become less likely to flower, and the flowers that are produced are often less showy and numerous. In order to keep these shrubs flowering, we cut them back to the ground and allow younger branches to fill in, a process called rejuvenation as the new growth produced is juvenile, as opposed to the mature wood that was removed.
While a lot of our shrubs will be getting a winter makeover, there are an important group of plants that should not be pruned during the winter. Our spring-flowering friends, such as azaleas, should be left alone during the winter months. To ensure the best floral display, these plants are best pruned immediately after they have finished flowering in the spring.
We also avoid pruning certain summer-blooming plants during the winter. Plants which produce flowering buds the prior year, otherwise known as flowering on old wood, cannot be pruned until after they have flowered. This group, which includes many hydrangeas, witch hazels, and quince, will not form any more flowering buds for the current year, as the flowers are all produced the year before. Pruning shrubs that flower on old wood would remove this year’s flowers, and one would have to wait until the following year to see any blooms.
Some plants that should NOT be pruned in the winter:
- Oakleaf and bigleaf hydrangeas
- Witch hazels
- Azaleas and rhododendrons