By Paul Nuhn, Extension Master Gardener
Winter is usually a gardener’s season of rest. Plants are dormant, and most maintenance tasks are put aside. Dormancy, however, makes late winter/early spring the best time to prune many shrubs and trees. The gardener can see the shape of the bare plants better, and the cuts are less disruptive than when the plant is growing. When full spring arrives, the plant will put energy into the new shape and desired size.
We prune shrubs to help control their size, to direct their growth, to make blooms more abundant, to rejuvenate, and to maintain health and appearance. February through March is the best time for most deciduous (leaf-dropping) shrubs, just before they start new spring growth. The exception to this rule is plants that will bloom in spring, such as lilacs, forsythias, azaleas, and weigelas. Their buds have already set, and if pruned now, though the plant will not be damaged, the blooms will be lost. Pruning them can be delayed until right after they bloom, but no later than early July.
See this Shrub Pruning Calendar for the best time to prune specific shrubs.
Pruning tools include pruners, loppers, and pruning saws. Make sure to use a sharp blade as because a dull blade can damage the wood. Also keep the tools clean. Wiping blades down with a bleach solution, rubbing alcohol, or a spray disinfectant as you go will make sure no diseases are passed from one plant to another.
Begin by removing any dead, damaged, or diseased wood. Next, remove any branches that cross or rub another, which can damage both. Removing them will also improve esthetics. Then select a group of strong, well-balanced branches to keep, and remove about a third of the plant’s bulk. This bold pruning will jump-start new growth on the remaining branches. As your plant grows, you will see dramatic improvement.
How to Prune
There are two basic types of pruning cuts: heading cuts, and thinning cuts. Heading cuts stimulate growth of buds closest to the wound. The new growth will be vigorous and often make shrubs bushier, but not smaller. Heading cuts are used when you are working on a hedge. When pruning a hedge, be sure to prune the sides of the hedge so they angle slightly inwards as they rise; this will allowing sunlight to reach to the bottom. Sides that angle outward generally have leaves at the top and are bare at the bottom.
Thinning cuts remove branches at their points of origin or attachment. Used in moderation, this gradual thinning reduces the shrub’s density without stimulating regrowth.
Make the pruning cuts correctly: for heading cuts, prune 1/4 inch above the bud, sloping down and away from it at a 45-degree angle. Avoid cutting too close, or too steeply, or the bud may die. For thinning cuts, prune just above side branches and roughly parallel to them; this which will encourage new growth outwards. Pruning sealer is not recommended.
Growth Habit
Understanding a plant’s natural shape or “habit” helps explain how it should be pruned. Shoots grow outward from tips. When branch tips are removed, the buds below the cut are stimulated to grow. Buds are located at nodes – where leaves are attached to twigs and branches. Shrubs have one of three growth habits – mounding, cane, or tree-like. Those with mounding habits, such as spirea, generally have soft, flexible stems and small leaves. Shrubs with cane habits include forsythia and nandina, and spread by sending up new canes from their base. Tree-like shrubs have woodier branches and include witch hazel and buttonbush.
Deciduous shrubs should be regularly pruned to maintain health. Maintenance pruning practices should begin after the first year of planting, or after rejuvenation.
To maintain mounding-type shrubs, prune only the longest branches. Make thinning cuts inside the shrub where they won’t be seen. This method reduces mounding shrubs by up to one-third without sacrificing their shape.
To prune cane-habit shrubs, remove the tallest canes near ground level. Then thin out crossing center canes, as well as those growing in an unwanted direction.
Tree-like shrubs can be challenging to keep in check. Prune to open up the center of the shrub. In our high-humidity region, plants need airflow. Keep the crown open and maximize light penetration with thinning cuts. Prune out branches that touch the ground and suckers originating from the roots. Wait until the end to make any heading cuts. Tree-like shrubs can tolerate removal of one-eighth to one-fourth of their branches.
When a shrub has been neglected for many years and become overgrown, normal pruning isn’t enough;. A severe form of pruning called rejuvenation pruning may be used. The entire shrub is cut back to 12 to 20 inches above the ground. The shrub will be unattractive at first but will quickly regrow to a better shape. Not all shrubs respond well to rejuvenation, but those that do are the ones that tend to get badly out of control. These include spirea, abelia, hydrangea, forsythia, beautyberry, flowering quince, viburnum and red- twig dogwood.
There is a second, more gradual technique for shrub rejuvenation. The first year, remove one-third of the oldest branches. The next year, remove one-half of the remaining old branches. In the third year, prune out the last of them. This method takes longer, but the shrub stays more attractive throughout the whole time.
Throughout the year, remove dead, diseased, or broken branches, making thinning cuts into healthy wood, below the affected removed area branches. Disinfect tools between cuts to prevent disease spread.
Lastly, notes on some specific shrubs: Most roses should be pruned into a vase shape with an open center. Climbing roses are an exception and should be pruned to create horizontal growth for maximum bloom. Azaleas’ natural layered growth pattern can be maintained with careful thinning cuts. Most overgrown azaleas can handle severe pruning down to approximately three feet. Different varieties of hydrangeas need different pruning techniques. A handout with details is available at https://mgnv.org/wp-content/uploads/2021/10/Pruning-Hydrangeas.pdf or in hardcopy in the Glencarlyn Library Garden’s Education Box.
A short video demonstrating pruning techniques is available at https://mgnv.org/glencarlyn-videos/#winter-pruning.
Source
French, Susan C. and Bonnie Lee Appleton. A Guide to Successful Pruning, Pruning Shrubs. 2009. Virginia Cooperative Extension. Publication 430-459