March 25 Column: Pruning Basics
‘Tis the season for pruning, right? Well, before you dive into it, I thought it would help to discuss some pruning basics first. For my column, I interviewed Tim Kohlhauff (seen at left), the Urban Horticulture Coordinator for Spokane County Extension. Here is a link to my column in today’s edition of The Spokesman-Review: Pruning correctly helps keep trees and shrubs healthy.
Tim is truly an expert on trees and pruning, especially from working as staff arborist at Spokane Country Club for 10 years.
As usual, there wasn’t enough room to share all of the information from Tim in my column, so you will find more tidbits below.
But first, I also wanted to share this week’s “Everyone Can Grow A Garden” video. In it, I cover the basics on pruning fruit trees:
OK, I hope the video was helpful. It was challenging shooting it on a sunny day (lots of shadows) and trying to shoot close-ups of small branches!
Here is more of my interview with Tim:
Why don’t young trees require pruning? You should wait until the tree is established, which usually takes 2-3 years. This allows the tree’s canopy to make up for roots that were lost when it was dug from the original nursery where it was grown.
Are there any types of trees or shrubs that should be pruned every year (other than established fruit trees)? There are some special visual effects that require annual pruning, like topiary or espalier. In this case, it’s not done for tree health, but to maintain a certain look. But in general, we don’t have to prune every plant every year.
Can you explain how pruning encourages new growth, and how that can be a problem? When we prune live plant tissue, we’re removing some of the “food factory” for the tree. This chemically triggers the plant to grow more, to replace what has been lost. Pruning in the dormant season (winter through bud break in the spring) can cause especially water-sprout-prone plants to push lots of new growth. Pruning in the early summer, after the regular flush of new growth in the spring, seems to slow plants down more than dormant season pruning. Having said that, I should say that some disease can infect pruning wounds made during the summer, so it’s good to check with the Master Gardeners or a certified arborist if you’re not sure about the risk to your tree or shrub.
I have a hawthorn tree that puts out all sorts of water sprouts after I prune it in late winter. Are there other trees or shrubs that react as badly to late winter/early spring pruning? I think some plants will react badly in response to any pruning, but hawthorns, fruit trees, as well as ornamental fruit trees like crabapples might respond this way. (Susan’s note: Tim suggested I try summer pruning our hawthorn and see if that works better.) There are also trees and shrubs that produce their flower buds the year before they bloom; this is sometimes called “blooming on old wood.” Pruning these plants aggressively will mean removing flower buds.
Are there bad times of year to prune? I try not to prune during spring from the time the plant starts to leaf out, until the leaves have reached their full size. This can cause some strange plant growth response, but more importantly, lots of diseases and insects are active at that time of year, and they can take advantage of those pruning wounds to damage the tree. I also avoid heavy pruning in late summer because if the plant sends out new growth in the fall, it won’t be tough enough to survive our winters.
What do you recommend folks do if a tree or shrub is too large for its place in the garden? If you have to heavily prune a plant every year to keep it small enough to fit the space, then maybe it’s time to replace that plant. This is especially true if your tree or shrub is too close to your house or under a power line. By the way, never prune a tree that is growing into a power lines or within 10 feet of them. Call your utility for more information about this, and please don’t get yourself hurt or killed trying to prune them yourself.
Why is it a bad idea to top trees? I hope most people know by now that topping is bad. Topping cuts are made at a random spot on a branch, rather than back to a side branch where they should be. Topping cuts don’t seal well, because the cuts are made in the wrong place, and this opens a tree to decay. Over time this weakens the structure of the tree, increasing the risk of one or more large branches breaking under stress. Topping also causes lots of fast-growing branches around the topping cut and within a year or two, the tree will be nearly the same size it was before topping. These new branches don’t have good attachments to the tree and are also more likely to fail in a storm. In other words, topping can lead to decay, shorten the life of the tree, and make it more expensive to maintain.
Is fall a bad time to prune? Late summer through fall is not an ideal time to prune because it sometimes causes regrowth at the wrong time of year. The new tissue may not fully mature before the weather turns cold, which means it may die over winter, and waste the plant’s energy reserves. The pruning wounds may also be infected by diseases active at this time of year, so check to see if late summer or fall pruning might leave your tree or shrub vulnerable. This can also happen because of spring pruning, so prune with caution at either time.
What is the timing of pruning flowering shrubs? First, learn when your plant grows its flower buds. Those that bloom on “old wood” set flower buds the summer before they bloom, so pruning between September and flowering will remove at least some of their flowers. Plants that bloom on “new wood” grow their flower buds the same season that they bloom, so pruning between leafing out and flowering may remove their blooms. In general, shrubs that flower in early to mid-spring, bloom on old wood; for example, lilacs, forsythias, and cherries. If they flower in the summer, they bloom on this year’s growth; for example, Russian sage, Butterfly bush, and hybrid tea roses. If you aren’t sure, you can always ask the Master Gardeners, or talk to your local nursery.
Thank you, Tim, for all of your help and information! Now, if you’re wondering how to ask your local Master Gardeners, here’s what you need to know:
Spokane County Master Gardeners: (509) 477-2181, email: mgardener@spokanecounty.org, website: http://extension.wsu.edu/spokane/master-gardener-program/.
Kootenai County Master Gardeners: (208) 446-1680, website: https://www.uidaho.edu/extension/county/kootenai/garden/clinic.
Find your local Master Gardener program: http://extension.wsu.edu/spokane/master-gardener-program/