Tidying, trimming, and pruning the winter garden
by Mary Robson, WSU Horticulture Agent
When leaves fall, their loss clears and opens garden views of shrub borders, which often starts gardeners wondering about winter pruning. What needs trimming? When's the best time?
One experienced gardener said, "Prune anytime your tools are sharp." This statement, while memorable, is misleading, since shrubs have different pruning requirements at different times of the year. Only one pruning task can be done anytime: removing dead, diseased, or broken limbs.
The gardener, itching to work outside on a mild winter day, may wander around looking for something to whack! But some caution and understanding of plant growth habits should be observed to avoid pruning at the wrong time.
And if the plants in your garden are strangers, unknown varieties, take a sample to a nursery or a WSU Cooperative Extension Master Gardener to get it identified before charging in to cut.
Let's start small, with perennial flowers. By December, the perennials that bloomed so vigorously have died back, leaving brown stubble and crumpled leaves. Shasta daisies, delphinium, tall bronze fennel, peonies, and many more summer-bloomers can all be cleared of dead foliage now, when they have no more beauty to contribute.
Some plants, like ornamental grasses and the grand sedum "Autumn Joy," go on looking good through winter and can be trimmed back in early spring.
Observe perennials carefully before slicing off old foliage. Next year's shoots may already be formed, tucked down into what's called the "crown" area at the base of the plant.
Cut off old growth and lift it away rather than tugging at the old attached stem. Yanking stems out of the ground can pull out or damage potential spring growth.
Peonies, for instance, have sharp points of deep red new shoots about an inch long at the soil surface; these will unfurl to stems in early spring. Keep clippers away from these growth points. One of the pleasures of winter clean-up in the garden is observing the new life waiting for spring.
After clearing out the perennial garden, add a protective mulch of two to three inches of any organic material. I like to use compost, tucking the plants in with an organic layer that will break down to add some nutrients for spring growth.
If the plant is marginally hardy and likely to freeze out, leave the top growth until early spring to protect the plant roots: Chrysanthemums, asters, and shrubby hardy fuchsias should be left strictly alone until the danger of hard freezes passes. And if your garden is in a cold microclimate, you may wish to postpone all perennial trimming until spring. Mulch instead.
Shrubs present even more confusing challenges. Think of flowering shrubs as divided into categories depending on when they bloom. If the shrub will bloom in early to mid-spring--such as camellia, rhododendron, azalea, forsythia, kerria, mock orange, or lilacs--don't touch them in winter except to remove broken limbs or diseased wood. These early-blooming shrubs have already formed flower buds for next spring and anything removed now cuts away potential bloom.
All spring-blooming shrubs should be pruned during flowering or directly after flowering is finished. Branches can be cut for forced bloom in the house during early spring, being cautious not to leave stubs on the plant. Cut branches for forcing when buds begin to swell.
If the plant blooms in summer or early autumn, trim it in early spring (late February or March). Pruning occurs just as the buds start to swell with growth. Examples are roses, buddleias (butterfly bush), hardy fuchsias, Hydrangea Paniculata ("Peegee" hydrangeas), and ceanothus. Most of these summer-bloomers produce new wood in spring that carries the emerging flower buds.
Hardy fuchsias may retain a strong woody structure of branches in a mild winter, then leaf out and bloom on existing branches. You'll be able to tell by the green buds swelling along the branches. In very cold winters, the entire fuchsia may be killed to the ground. Small new shoots will emerge from the crown area to expand into branches and bloom in August and September.
A word of caution about winter damage: If we have a severe winter, wait until later in spring before deciding that a shrub or tree has been killed from cold damage. Sometimes plants will sustain apparent severe damage, but retain live wood or roots which don't start leafing out until May or June. Hardy fuchsias are among the shrubs which may behave that way.
Vines can entangle the gardener in further confusion about pruning practices. Wisteria (Wisteria sinsesis) should be allowed to grow until a sturdy woody framework is formed, for about the first three years. Leave the woody shape, then cut back new growth produced during the year to the second or third bud off the framework, about six inches from the main trunks or branches. Do this in late winter when the flower buds will appear more plump and prominent than the leaf buds. The plant blooms on "spurs" which will be easy to identify once you've looked closely at the plant. It may also produce long, stringy leafless shoots. In spring, cut these leafless shoots out completely. A late-summer pruning may also help to prevent sprawling growth. If wisteria is left to sprawl unpruned, it will cease to bloom. Be sure to provide a good support system for wisteria, as it will grasp and wrap itself around any available stem hold, such as the downspouts of a house, if it's not kept controlled.
Clematis, wonderful blooming vines, are pruned in different ways, depending on their season of bloom. Some clematis, such as the evergreen Clematis armandii, produce flowers on new growth shoots off existing stems and should be trimmed lightly after bloom.
Others, such as large-flowered hybrids like Clematis x jackmanii, should have all the previous year's growth cut off in late January or February.
By now observant readers will have realized that none of this pruning must be done in December. What can be done is to ask for a gift of a good book on pruning. Pruning, by Christopher Brickell (Simon and Schuster 1979, and later editions) has clear diagrams. Another helpful one is All About Pruning, Ortho publications, 1978. Both list specific common garden shrubs and vines with their pruning requirements. Sharpen those tools and wait for early spring!