Fall is a transition period for plants, as they prepare for the harsh winter. Some benefit from an autumn pruning, while others risk being weakened before the winter. It is therefore crucial to distinguish between the different categories.
Plants not to prune in the fall
- Trees and shrubs with spring flowering: They form their flower buds on the previous year's wood. An autumn pruning would remove these buds and compromise the following spring's flowering. These should be pruned after flowering. Among these plants are:
- Serviceberry, Aronia, Azalea, Flowering Cherry, Forsythia, Magnolia, Rhododendron, Van Houtte Spirea, Lilac, Weigela, as well as many fruit trees.
- Trees prone to bleeding (exudation): Some trees, such as birch, maple, and walnut, tend to "bleed" profusely with sap if pruned in the fall or winter. Wait until early summer to prune them, when the sap flow is less intense.
- Conifers: Most conifers are pruned in the spring or early summer to promote good healing. An autumn pruning can weaken them before winter. Exception: Some conifers such as cedars and junipers can be lightly pruned in the fall to maintain their shape.
- Cold-sensitive plants: Some species, particularly young plants or those recently transplanted, will be weakened by an autumn pruning. Wait until spring to prune them, which allows them to build up their reserves before winter.
Plants that can be pruned in the fall
- Trees and shrubs with summer or fall flowering: They flower on the new wood of the year. An autumn pruning can stimulate growth and flowering the following year.
- Butterfly Bush, Hardy Hibiscus, Hydrangea paniculata, Shrubby Cinquefoil, some roses.
- Evergreen shrubs: Light shaping and removal of dead wood can be considered. Examples: boxwood, holly, yew, mahonia. The main pruning, however, remains in the spring.
- Deciduous perennials: Some perennials benefit from an autumn pruning to remove senescent parts and promote vigorous spring development. Evergreen perennials are generally pruned in the spring.
Flowering: impact on pruning time
- Flowering on previous year's wood: Pruning should be done immediately after spring flowering.
- Flowering on current year's wood: Pruning is appropriate in autumn or late winter.
When and how to prune?
After the leaves have fallen, but before the first frost arrives.
Good practices:
- Use clean and sharp tools for clean cuts.
- Make cuts just above a bud or a lateral branch.
- Systematically remove damaged branches and dead wood throughout the year.
- Eliminate harmful branches (tangled, centripetal development).
- Limit pruning to 20-30% of the branches per year.
- Remove low branches on the trunk.
- Preserve the terminal leader (except for specific exceptions).
If in doubt, it is recommended to seek the expertise of a horticultural professional. Careful and adapted pruning contributes significantly to the health and aesthetics of your plants throughout the year.
