Dormancy is the best time to prune your deciduous trees. Below, we outline three benefits of pruning trees in the dormant period. So don’t wait for the leaves to come in before doing routine pruning!
1. Lower risk of disease
Pruning cuts leave behind wounds, and just as with people, tree wounds are vulnerable to disease. Many diseases spread from tree to tree by hitching a ride on beetles and other flying insects. These insects are attracted to the sap that oozes out of fresh pruning wounds; as they feed on the sap, they spread disease right into a fresh wound. From there, disease can easily enter the tree and start spreading rapidly to every corner of the tree.
If pruning wounds are made in winter, sap will still ooze out, but insects won’t be around to feed on it—or infect the tree with disease. By the time spring rolls around, and insects are active again, the pruning wounds will no longer be oozing the sap that attracts them.
So pruning your trees in winter and early spring reduces the risk of infecting them with potentially fatal disease. This is especially important if you have species with high disease risk, such as ash, oak, and elm.
2. Less stressful for the tree
Every time you cut a branch from a tree, that tree has to recover by containing the wound internally and sealing the wound over with new wood. This recovery process consumes a lot of the tree’s resources. So it is best to prune trees when the tree has more resources rather than less. And trees have more reserve resources in dormancy than any other period.
You can think of dormancy like hibernation. In fall, when the squirrels and bears are fattening up, storing reserve energy for winter, trees are storing up their reserves as well. If you cut branches from the tree when their reserves are at their highest (i.e., winter and early spring), they will have an easier time repairing the damage from these cuts. Think of it like making a major car repair when you have lots of money in the bank (sorry for mixing metaphors!).
When spring rolls around, trees consume their reserves to open buds and begin flowering. If you prune at this time, the tree’s reserves will be low, and recovering will be more stressful—a bit like being hit with a major car repair when you’re strapped for cash!
Pruning can be beneficial for a tree in the long term, but in the short term pruning stresses the tree. This stress is reduced if you prune your tree in the dormant period of winter and early spring.
3. Easier to assess the structure of the tree
Many homeowners assume that tree trimming needs to happen when the tree has leaves. “Otherwise,” clients often say, “you can’t tell which branches are dead!” (We can, actually!) This would make sense if arborists only ever pruned trees to remove dead branches, but there are other more important pruning objectives, such as improving the structure of the tree.
Structural pruning assesses how load is distributed throughout the canopy and identifies parts of the tree that are most vulnerable to breaking in a storm. By removing weight in the right places, a skilled arborist can significantly reduce the risk of storm damage.
It is much easier to assess the structure of a tree and identify the right cuts when the leaves are gone. Winter is a bit like an x-ray for a tree that reveals the “skeleton” of the canopy. Rather than just looking at a wall of green, the arborist can track how load is distributed along the branches and trunk—making it easier to identify the best places to make cuts.