There is a common misconception among homeowners that winter is a poor time to prune trees and shrubs. Actually, for the majority of trees and woody shrubs in most growing areas, winter pruning is beneficial. A closer look at tree structural pruning, insect and disease control, impact on surrounding plantings and a need to practice and hone skills will lay a firm base that supports winter pruning.
Trees and shrubs provide many benefits to the landscape during the growing season. The main reason for planting and plant selection is often aesthetics. In the winter, as deciduous trees lose their leaves, a new aspect of tree aesthetics is revealed: structure. Healthy trees need a sound structure to support healthy growth. However, in the warmer months, this aspect of a tree is often hidden. Winter is the perfect time to enjoy what is termed “winter interest,” and the perfect time to prune for it.
With care and skill, a trained arborist can highlight a tree’s natural features and still maintain a healthy platform for growth with winter pruning. Bare trees become living sculptures that promote properly directed spring growth and visual appeal at the same time. Flowering crabapples (Malus hopa) are a prime example of the type of landscape tree that is best pruned in the winter for form and structure.
The second reason winter pruning can benefit trees and shrubs is insect and disease control. Many pathogens are spread throughout the plant world from one victim to the next through insects. Often these insect vectors are attracted to wounds on trees that intrinsically happen through the pruning process. Pruning to avoid excessive wounding (i.e. proper cuts) coupled with winter pruning cycles short circuits the pathogen’s mode of transportation and limits spread.
A prime example of this relationship is the American elm (Ulmus americana). The elm bark beetle, attracted to recent wounding on elm trees, spreads the fatal Dutch elm disease from one tree to the next. This problem can be mitigated when the tree is pruned in winter. Oak wilt in some climes is another example. However, all trees and shrubs can benefit from this pruning strategy.
Problems with bark peel due to heavy sap flow lessen or disappear in the off-season. Thin-barked trees are more resistant to the scuffing of boots, ropes and dropped limbs. The unsightly and sometimes downright sticky and smelly sap ooze from fresh cuts is abated as well. While not a major problem for most trees, it will keep your clothes and equipment tidier.
The next benefit of winter pruning has little to do with the actual tree and more about the environment in which it lives. Trees are individual features of a landscape. While often the major feature, trees do not exist in the landscape alone. Paired up with complementary annuals, perennials and hardscape features like water gardens, trees help form dramatic and beautiful yards, gardens and parks.
Wintertime allows arborists access to trees and shrubs without causing damage to other plantings that are also dormant. In winter, the normally delicate hostas, tulips and any other understory materials avoid the inevitable bent, broken or trampled leaves and stems. Water features are often covered or frozen over, allowing sawdust and other debris to be easily removed. Frozen yards and natural areas offer ideal conditions for equipment placement with impunity from ruts and soil damage. Also, the work can often be completed more quickly, saving money as well as limiting damage. Wildlife cannot be ignored in this strategy. Beneficial colonies of honeybees, for example, can be worked around with little disturbance to the insect.
Trees that are habitats for wildlife are often best addressed in the winter. Birds head south, spring-born young are not hanging about, and many species hibernate in winter.
This article would be remiss if it did not mention the downside of winter pruning. As with all things, there are limitations and drawbacks. These drawbacks often have little to do with plant health and more to do with efficiency. For instance, shrubs in the Taxus family (yews) can be pruned in the winter, but the flush of growth in spring and early summer typical of these plants makes winter pruning a bit fruitless (pun intended). Winter efforts are lost quickly, as the plant rapidly puts on new growth.
Other examples are fruit trees. These may need a summer touch-up to reduce breakage from heavy fruit loads. Unless you have a crystal ball, this would be hard to predict in the off-season. Also, finding fine dead wood in sprawling trees, while not impossible, is much easier when the tree is in leaf. Pin oaks are a prime example of this. No one likes to return in the spring to redo missed deadwood.
Winter is also an excellent time to hone pruning skills and learn new ones. Tree structure is more apparent and cuts are more visible before and after pruning. Bark peel is rarely a problem, allowing climbing of small trees not only for pruning practice, but climbing training as well. Understory plants are also less of an issue for new pruners and climbers when learning the basics. Generally speaking, the pace and overall workload is a bit slower, so the learning curve does not bite as hard into the profit curve when training in the winter.
The three aspects of structural pruning, insect and disease control, and surrounding plantings and wildlife taken together form a strong synergistic basis in favor of winter pruning. Any of the three alone is a good argument, but in combination the reasoning is clear. The great majority of trees and shrubs can be pruned effectively, properly and efficiently any time of the year. However, wintertime offers unique circumstances that the savvy arborist can use to his benefit and profit, all while developing and maintaining a stunning landscape.