Pruning Basics
Keeping track of which plants to prune when may seem overwhelming, but for most flowering trees and shrubs, one simple rule applies: If it flowers on old wood—stems that grew last year and formed flower buds on them—wait to prune until after it finishes blooming in spring. Many spring-flowering shrubs bloom on old wood, and pruning them in winter means cutting off some or all of the year-old growth with the flowers of the coming season.
Other trees and shrubs bloom on new wood that grows during the current season. Late winter is the ideal time to prune them because cutting them back encourages vigorous new growth that will produce flowers in the upcoming season.
While spring-flowering plants are best pruned in spring or summer, you should remove dead, diseased, or storm‑damaged branches at any time of year, regardless of bloom time.
1. Plants That Bloom on Old Wood
These popular shrubs bloom on old wood and should be pruned after they finish flowering, in spring or early summer. You’ll enjoy all of the spring blooms and be able to easily see the shape and health of the plant, as well as any dead tips or branches.
Lilacs
The flowers of these spring-blooming shrubs are pleasant to look at and have a lovely scent, but you won’t enjoy either of those benefits if you prune lilacs heavily in winter. Unfortunately, hungry deer are quite capable of nipping off every growing tip on a young lilac and all the buds set last year, leaving you with no blooms in spring. To protect your lilacs against hooved herbivores, install tall fencing or cages around your lilac bushes.
Forsythia
Bursting forth in sprays of yellow blooms while everything else is still brown and dormant, forsythia provides a splash of color when the daffodils are starting to bloom. The shrubs set their flower buds on one-year-old growth, so wait to prune forsythias until they finish blooming in spring. Complete any major pruning by early summer so new growth has time to mature before winter.
Azaleas and Rhododendrons
Like other spring bloomers, shrubs in the Rhododendron genus bloom on one-year-old wood. While it’s tempting to have a go at them with the pruning shears while you are out and about in winter, pruning for shape or aesthetics will remove the buds that flower in spring. Wait to prune your azaleas and rhodies until they are done blooming.
Magnolias
Regardless of the variety, magnolias also set next spring’s flower buds on the previous season’s growth. A winter pruning removes many of those buds. Instead, prune these shrubs after the flowers have begun to fall off in late spring to avoid cutting off the buds that will be next year’s blooms.
2. Conifers in Cold Climates
In areas with a combination of severe winters, intense winter sun, and strong winds, pruning evergreens in winter makes them more susceptible to moisture loss and winter burn.
Skip cosmetic pruning of conifers during the coldest part of winter and delay shaping trims for ornamental yews, junipers, boxwoods, and tree-type conifers like dwarf spruces until after the new flush of growth in spring. If you miss that time window, you can still lightly prune them in summer.
3. Stone Fruit Trees
While many fruit trees, such as pear trees, are pruned in winter, stone fruit trees are typically pruned in summer. The reason for this is that peaches, plums, cherries, and other stone fruits are at higher risk of infection when pruned, because pruning cuts are injuries to the tree. The fungal diseases and bacteria that cause cankers in stone fruits are more likely to gain entrance through a pruned branch in winter, when the tree takes longer to seal over the wound.
Prune stone fruit trees in the warmer months of summer, but not so late that new growth resulting from pruning won’t have time to harden off before winter.
4. Maples, Birches, and Willows
Pruning maple trees, birches, and willows in winter is not recommended because they are prone to excessive sap running from wounds. Starting in midwinter and continuing until spring, these trees have a heavy sap run, one of the reasons sugar maples are tapped in late winter to make syrup.
Although younger trees sometimes need a bit of pruning, unless there’s a broken branch, it's best to wait until they have fully leafed out in summer. While pruning these trees won’t leak so much sap that they die, an excess amount of sap can make a sticky mess, attract insects, and stain the bark below the pruning cut.
5. Certain Types of Hydrangeas
When it comes to pruning, hydrangeas are a mixed lot. The key to determining which season is appropriate for pruning your hydrangea is to identify which type of hydrangea you have.
Bigleaf hydrangeas (H. macrophylla) and oakleaf hydrangeas (H. quercifolia), as well as mountain hydrangeas (H. serrata), bloom on old wood. All three should only be pruned after the flowers fade. The rest of the hydrangeas, including the popular smooth hydrangea (H. arborescens) and panicle hydrangea (H. paniculata), bloom on new wood and can be pruned in winter.
However, there are newer hydrangea varieties called reblooming hydrangeas that bloom on both old and new wood to extend the blooming time. Popular varieties include 'Endless Summer' and 'Bloomstruck' hydrangeas. On these hydrangeas, the buds on old wood are the first to flower in springtime, and those set on new wood bloom later in the season. You can prune these varieties at any time (you’ll always be disrupting some blooms), but pruning them after the first flush of blooms fades has the least impact on flowering.
