If you're dying to get out in the garden no matter the weather, then the prospect of winter pruning will thrill you. If you thought you were finally getting a break from gardening chores then well, not so much. But late winter is the ideal time to prune most woody ornamentals, as the branch structure is clearly visible, and plants will suffer less damage than if pruned in late summer or fall. 

There are exceptions, though, as pruning some species now will remove overwintering flower buds and leave you sorely disappointed come springtime. Whether you're needing some major renovation on those overgrown shrubs, or just want to tidy up a few errant twigs and sprigs, it's a good idea to know what's what. Here’s a list of what to prune now, and some general tips on why, what, and how you should be pruning:

Why prune?

Pruning is done for several reasons, and at various times:

• Disease or damage: This should be accomplished as soon as it occurs, regardless of the time of year. Broken branches should be recut properly. Be sure to remove all of the dead portion, cutting back to a live bud or branch, or removing at the base.
• Suckers and water shoots: Suckers are long, non-branching shoots that emerge from the base of a tree. Water shoots are similar, but grow at right angles to the branches. These should be removed at their base, as they will never grow attractively and will usurp energy. If you have a grafted tree you must remove any suckers that grow below the graft. The graft can usually be identified as a widened, callused section near the bottom. The rootstock of a grafted tree is different from the desired top growth, and suckers from those roots will compete with and possibly overtake the grafted portion if not removed. FYI, fruit trees and Japanese maples are very commonly grafted.
• Crossing branches: Best done (and observed) in dormant season. Remove branches that will eventually grow into each other to keep the tree well-shaped and healthy.
• Encouraging flower/fruit production: Many fruiting plants benefit from having old fruiting wood removed so that energy can be directed to the newer stems where fruit will be produced. Some flowering species, such as wisteria, will bloom better if excess green growth is removed, thus redirecting the energy to flowering. Hydrangea, viburnum, and others will benefit from symmetrical thinning--removing some of the oldest and tallest wood at the base, then cutting additional stems back to a main branch. This will open up the plant which will enhance the beauty, provide for more air circulation to reduce foliage disease, and allow sunlight to better reach all parts of the shrub. Timing depends on when the plant blooms. Spring bloomers usually winter over flower buds, so should be pruned right after flowering finishes. Summer bloomers flower on new growth, so pruning should be accomplished by early spring.
• Shaping: Some plants lend themselves to shaping into balls, squares, etc.—usually small-leaved evergreens like boxwood or yew. Other plants should be pruned to shape by thinning or by removing stray shoots that spoil the natural shape of the plant. Forsythia is an example of a plant that is frequently abused and tortured into unnatural, heavily pruned shapes. Always follow the plant’s own growth habit and outline when deciding what to prune. In northern zones, avoid flat-topping anything—this makes it much more likely to suffer snow damage.
• Size: If a plant outgrows its assigned space, it may be possible to restrain it with thoughtful pruning. Most shrubs will not be enhanced by simply topping or shearing—it is better to cut back individual stems to a main branch or to the base. Plants that do not branch, like nandina and mahonia, should never be topped—this will eventually result in bare stems at the bottom with all the foliage at the top. Instead, prune tallest stems out at the base if downsizing is needed; otherwise, prune stems at staggered heights to keep the plant furnished from top to bottom.
• Hedging: Hedges should never be pruned straight across the top and sides like a rectangle. The basic shape when seen from the end should be like a rounded letter A. In this way, there will not be a wide “shelf” to catch and be damaged by heavy snowfall, and sunlight will find its way to the bottom of the shrub, preventing the plant from shading itself and losing foliage on the bottom. Pruning and training should begin at planting. It can be difficult to think of trimming newly planted shrubs when we’re anxious for them to grow, but the proper shape must be established early. Otherwise, a harder pruning later will likely be necessary, and the hedge will never look as good as it might have. Most hedges should be trimmed just after the spring growth flush, with faster growing species perhaps needing a second trimming by late summer to remove long, spindly shoots.

How to prune?

• Make stem cuts at a 45 degree angle--the top of the cut should be on the same side as the bud, and 1/2 " above a live bud; or, take all the way back to the branch.
• Choose an outward facing bud so that new growth will not be directed toward the center of the plant. This is especially important for hybrid tea roses which perform best with an open vase shape. This allows for proper air circulation to reduce disease, and for sunlight to reach all parts of the plant.
• Make sharp cuts with no ragged edges--use the proper size tool and make sure blades are sharp.
• When pruning branches from a trunk, leave the branch collar rather than cutting flush.
• When pruning large branches, make an undercut first to prevent tearing the bark.
• Wound dressing or paint is not generally recommended.
• Prune at the correct time. Prune in dormant season, at least by the time new growth begins to break for summer flowering plants. Prune just after flowering ceases for spring flowering shrubs and trees. Refrain from pruning soon after the first flush of growth in spring--plants use up food stores in this process and need time to rebuild. Pruning too often at this stage can cause greatly reduced growth and vigor.
• In general, never remove more than 1/3 of a plant at any one time.

When to prune?

Prune in dormant season in late winter

Summer-flowering deciduous shrubs and vines:

• Buddleia (Butterfly Bush): These can be cut almost to the ground if overgrown.
• Callicarpa (Beauty Berry)
• Camellia sasanqua (usually fall-blooming)
• Caryopteris (Blue Mist Shrub): Can be cut to ground to control size.
• Clematis Type III: Summer to fall blooming types like jackmanii—cut down to 3 strong pairs of buds per stem.
• Clethra (Summersweet)
• Cotinus (Smoke Tree)
• Cotoneaster: as for Malus sp.
• Crataegus (Hawthorn): as for Malus sp.
• Hibiscus syriacus (Rose of Sharon)
• Hydrangea: Prune out 1/3 of older stems at base each year, then for shape/size: newer H. macrophylla varieties that bloom on new wood (‘Endless Summer’,); H. paniculata (Pee Gee, ‘Limelight’, Little Lime); H. arborescens (Smooth Hydrangea, Annabelle, Incrediball, Invincibelle)
• Ilex verticillata (Winterberry): as needed for shaping
• Itea (Sweetspire)
• Lagerstroemia (Crape Myrtle): No one needs to cut these as harshly as is commonly practiced.
• Malus sp. (Apples, crab apples): While pruning in late winter may remove some flowers and fruit, it will help to prevent fireblight and other disease vs. pruning in summer
• Roses: Hybrid tea, climbing, & old-fashioned roses should be pruned just before new growth begins in spring. When dead-heading later in the season, cut back to the first five-leaflet leaf, as cutting above three-leaflet leaves results in blind shoots that do not bloom. For climbing roses remove older canes at the base, as the best blooming stems are those produced from the base of the plant the previous season.
• Sorbus sp. (Mountain Ash): as for Malus sp.
• Viburnum: ok if hard pruning is needed to control size. Otherwise, wait until flowering has ceased for light pruning.
• Vitex
• Wiegela
• Wisteria: Pruning is generally done to control size and promote flowering—twice yearly pruning is recommended. Plants bloom on previous season’s growth. Cut back new growth to five to seven leaves per stem in July-August. If needed to control size prune those same stems in winter to 3 to 5 buds—that is the wood it will flower in the coming season. Plants may take several years to achieve maturity before they bloom.

Deciduous Shade Trees:

• Pyrus calleryana (Callery Pear, e.g. ‘Bradford,’ ‘Cleveland Select’): Really you would wait until the white flowers have bloomed, but they’re so invasive and weak wooded that they need to go away anyway. Hack at will.
• See list of what NOT to cut

Broadleaf Evergreens:

• Abelia: smaller, more compact species will likely only need tidying for shape. A. grandiflora and other large growing types can be cut to the ground if overgrown.
• Buxus (Boxwood)
• Euonymous
• Ilex (American, Chinese, English, and other evergreen hollies)
• Ligustrum (Privet)
• Nandina: Never top these shrubs as they will die out on the bottom but grow heavy foliage on the top. If pruning for size is needed cut tallest stems all the way to the base or cut several stems at varying heights to keep the overall look full.
• Osmanthus
• Photinia
• Viburnum: Best time if hard pruning is needed to control size. Otherwise, wait until flowering has ceased for light pruning. Periodic thinning is beneficial.

Conifers:

• Juniper: Trimming individual stems is best. Never cut more than one fourth to one third of the foliage at one time. Shearing tends to create a thick layer of foliage on the outside that causes the interior and lower foliage to die out as the sun never reaches there. On large or old specimens this is unavoidable and natural—there will be a “dead zone” towards the center where light does not penetrate. NEVER cut back into old wood that does not have new growth—new needles will NOT regenerate. Bare or broken branches without new growth should be taken back to the trunk or base. It is almost impossible to severely prune a juniper for size successfully, so care should be taken in variety selection before planting.
• Picea sp. (Spruce): Spruce and firs will not regrow from the ends if they are cut. Instead, they will form lateral buds from which new growth will occur. While not harmful, it may lead to a unattractive and undesired shape.
• Taxus (Yew): Yews are one of the few conifers that will regrow from a hard pruning—as much as 50% can be cut without damage. They also tolerate frequent shearing so have little to fear from overzealous landscapers and husbands with new power tools. For a more natural look, individual stems and branches may be easily trimmed into shape.
• Thuja (Arborvitae): Ditto what we said for junipers. These tend to be very tidy growers, so if the proper mature size is selected little pruning will be necessary.

Fruits:

• Blackberry: Remove weak canes and cut laterals to 12-15 inches. Old fruiting stems should have been removed in the fall.
• Blueberry: Remove old fruiting wood at base. Leave 3 each of 1-, 2-, and 3-year-old canes.
• Fig: Remove any diseased, broken, or weak branches to promote strong new growth.

Plants NOT to Prune in Winter

(Prune these just after flowering ceases unless otherwise noted)

Spring blooming shrubs, vines and ornamental trees:

• Amelanchier (Serviceberry)
• Azalea
• Camellia that did not bloom in fall, usually C. japonica and hybrids
• Cercis (Redbud)
• Clematis Type II: These should be pruned to a framework in late summer, as they will bloom on both old wood and new wood. Alternatively, you can prune as for a Type III, but you will sacrifice your spring blooms
• Forsythia
• Gelsemium (Yellow Jasmine)
• Kalmia (Mountain Laurel)
• Loropetalum (Chinese Fringe-Flower)
• Hydrangea macrophylla: Old-fashioned mopheads and lace caps: e.g. Nikko Blue, variegated lace cap. If you have purchased a mophead or lace cap hydrangea within with last 10 years or so, it is likely a newer variety that will bloom on new wood, as growers started switching to these types with the advent of the Endless Summer Hydrangea.
• Hydrangea quercifolia (Oakleaf Hydrangea)
• Magnolia
• Pieris: (Japanese Andromeda)
• Prunus (Ornamental fruit trees—cherry, peach, plum, etc.)
• Pyracantha
• Raphiolepsis (Indian Hawthorn)
• Rhododendron
• Salix sp. (Pussy Willows)
• Spiraea vanhouttei (Bridal Wreath Spirea)
• Syringa (Lilac)

Conifers:

• Pine: The growing points are only at the terminal ends of the branches, so once they are cut it will eventually leave a dead stub. Up to 2/3 of the new growth, or “candles” may be cut before they are mature. There is only one flush of new growth per year.

Deciduous Shade Trees:

• Birch, maple, elm, walnut, and dogwood tend to bleed sap heavily when pruned in winter. While not particularly damaging to a healthy tree, it will be less messy to prune in summer.