From now until about mid-March, most evergreens can be pruned without fear of injury to the plant. This includes many common foundation shrubs such as arborvitae, boxwood, holly, juniper and yew. Pine and spruce trees are also safe to prune, although timing is less crucial with those species.
Pruning in late winter to early spring is a good time for evergreen shrubs because the flush of new growth in the spring will fill in any bare spots and cover the pruning wounds. Evergreen shrubs are also unlikely to become stressed from losing some of their branches at this time of year. This is a good time to make a size reduction, improve shape, remove witches’ brooms caused by shearing, remove dead or damaged branches, and/or get the hedges off of walls or other structures.
If you are used to clipping hedges, continue to do so in the late spring and summer months but you can take advantage of this time too.
For all evergreen shrubs, remove larger older branches and leave small tender growth when possible. The bottom of shrubs should also be wider than the top, even for hedges. Visualize the sides of the shrub sloping like the letter A. (For a hedge, the A-line would only be evident on the ends.)
Pruning should always attempt to maintain the natural shape of the plant. There are many variations of shape within species, for example, junipers may be rounded, mounded, pyramidal, creeping, weeping, spreading or layered. Observation of plant growth is the best indicator of form.
Junipers have scaly needles and are the least forgiving of the evergreens. (Cedar is a type of juniper.) Cutting a juniper back to old interior wood will leave a permanent bare spot. Instead, try thinning foliage by removing branches here and there to open the exterior. Branches can also be pruned back to the last green branch or bud coming from it.
Arborvitaes, boxwoods and yews will rejuvenate, albeit slowly, from heavy pruning. Arborvitae have scaly needles like junipers but the scales are softer and pressed into flat fan-like shapes. Boxwood have small, shiny, round or oblong leaves. Yews have soft individually born needles that are typically about an inch long. They also sometimes have red berries that can help to identify them.
To rejuvenate and reduce the size of arborvitaes, boxwoods and yews, primarily use thinning cuts. Thinning lets light into the center of the shrub where it can stimulate latent buds without leaving large bare spots. Cuts in the center of the shrub also help to stimulate those buds to break dormancy. To maintain shape, focus on removing vertical shoots and leaving horizontal ones.
For hollies, pruning varies a little more with the specific type and goal. Thinning is a good option for all. Selective pruning can be used to shape and to reduce the size of the plants. For suckering hollies, thin by cutting large stems back to the ground. This will also encourage new growth.
Pines and spruces can really be pruned anytime in the winter, spring, and early- to midsummer. Pines have longer needles that are always clustered together in little bundles of two, three, five or more, depending on species. Needles may be stiff or soft. Spruce have short stiff needles that are born individually on the branches.
Use selective pruning to shape and thin pines and spruces.
Another option for pines is to wait until new growth appears and prune it to maintain or improve plant size and shape. New growth of pines is referred to as candles because the needles are tightly bunched and extend out from the fan of needles below like a tapered candle in a stand. Use shears, pruners or fingers to clip or pinch off about half of each candle. Expect lots of sticky pine sap.
Avoid pruning any shrubs from August through the first hard freeze of the fall. Pruning in late summer can stimulate new growth that will not have time to harden off before winter. Late summer and fall pruning wounds also take the longest to heal and leave the plant exposed to disease-causing organisms for a longer period of time.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show.”