What to prune and what not to prune now

I was recently asked about what to prune now and what not to prune. Why do we prune in the first place?
Proper pruning promotes plant health, which is why we start by cutting out dead, dying, crossing, rubbing, diseased or damaged parts. Also, pruning encourages flowers and fruit production. Or, if done correctly, it can actually reduce overproduction of fruit.
It may be used to encourage a particular form or to improve appearance. You may need to prune to protect people and property, such as removing limbs that block traffic signs or hang into walkways.
What not to prune now? Do not prune forsythia, quince, lilac and other spring-flowering shrubs. You will cut off the flower buds and not have flowers this year.
Prune spring-flowering shrubs after they bloom. Do not prune roses now. The best time to prune roses is after Tax Day, April 15. Rose stems often develop canker disease/damage, because of our dry, sunny winter weather. By waiting until April, you can see where the cankers have developed and then prune. If you prune too early, cankers can still develop and you will have no stem left to prune out without destroying the bush.
Some horticulturists say it’s OK to prune maples, birches, beeches, poplars, elms and willows now even though they will “bleed” (weep sap). They say the bleeding is not harmful, but I disagree.
Often our soil is dry through the fall and winter and trees don’t have a water reserve in their systems. Bleeding could reduce a tree’s water content and its strength. I suggest pruning these weepers in late spring or even late summer. Wait on pruning grapes until March to April.
Do prune any trees or shrubs that experience unexpected damage, such as from bad weather. Although most evergreen trees and shrubs need little pruning, winter is a great time to prune them. Prune summer-flowering shrubs, such as potentilla and spirea, and deciduous trees and fruit trees in late winter or early spring.
Supposedly pruning in late winter (four to six weeks before spring thaw begins) rather than early winter allows for more rapid wound closure. No matter when you prune, try to remove only 25 percent of growth per year.
When you are researching how to prune online, look for information from Utah State University or Colorado State University. Both states have conditions like ours. Here’s one on pruning fruit trees from CSU: https://extension.usu.edu/yardandgarden/ou-files/PruningHandout-OY-Mar2017.pdf
When plants have been pruned properly, it’s hard to tell they have been pruned at all.

JoAnne Skelly is associate professor and Extension educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.