Pruning Trees & Shrubs
How And When To Prune You Woody Ornamental Plants
Pruning is probably the yard job that gardeners fear most. Many people are leery about cutting into a healthy plant, thinking they’ll harm it or even kill it if they don’t do the deed right.
But pruning is an important and necessary task for most woody ornamental plants. It can remove dead or diseased tissue and help keep plants healthy. It can open up overly dense growth and improve air flow, thereby discouraging disease. It can rejuvenate old plants by spurring new growth that flowers better. And it can improve the looks of plants and correct a lot of potential problems that trace back to siting mistakes, including keeping too-big plants under control and keeping overgrown branches away from windows, driveways and intersections.
Different goals of pruning
The type of pruning you do depends on the reason for doing it.
Sometimes, nothing more is needed than cleaning out any dead, diseased, bug-injured or broken branches, such as at the end of winter or following a wind storm. Removing dead or damaged wood can be done at any time of year and should be done as soon as possible after the damage occurs.
Many landscape plants benefit from occasional thinning or light annual pruning in which the idea is to keep the plant from getting too dense. This type of pruning involves selectively removing whole branches and twigs, especially those that are growing inward or rubbing together.
Many plants also benefit from “heading back,” which is done primarily to control overly vigorous growth and to improve the look of the plant. This removes weight from the branch tips (preventing weak branches from sagging) as well as neatens the plant by shortening wayward branches.
Sometimes trees and shrubs become overgrown when they‘re not pruned for several years. When that happens, flowering plants may not bloom as well. In this case, “rejuvenation pruning” can be done in which some of the larger branches are removed or shortened. In the case of multi-stemmed plants such as lilac, forsythia, mock orange, deutzia and redtwig dogwoods, stems that are three or more years old can be removed to the ground. The idea in both cases is to stimulate new growth that will flower better.
When removing big branches (which includes “raising up” a tree’s lower branches), make a three-step cut as shown in Illustration 1 to prevent the branch from tearing bark as it falls away. Always cut to the outer edge of the little ring (the “branch collar”) that can be seen at the point where branches attach to one another and to the trunk. Do NOT leave stubs out from the collar and do NOT cut into the trunk.
When shortening branches, cut back to just above a branch or bud that’s facing in the direction you want the new growth to go. (See Illustration 2.) Also cut back to a branch that’s about one-third the size of the parent branch.
When to prune
Timing is important in knowing what to prune when. One good rule of thumb to remember in pruning flowering shrubs is that varieties that bloom from mid-June on (from buds that form in the spring) should be pruned at the end of winter or early spring. Varieties that bloom in early spring to mid-June (from buds that formed last summer and fall) should be pruned immediately after they’re done flowering.
Most needled evergreens are best pruned at the end of winter and again in June, if necessary. Boxwoods, privets and Japanese hollies also can be pruned at these times. Light neatening cuts on evergreens also can be made again up until mid-July, if needed.
The worst time to prune is late summer and fall when cuts will encourage new growth that may not harden off in time for winter. It’s also not good to prune in a drought because you don’t want to encourage new growth when the plant is struggling just to keep its current growth alive.
If you can’t wait until spring, you can prune in winter once leaves drop. Just keep the cuts to a minimum because each cut is an area where moisture can escape heading into winter.
Some pruning do’s and don’ts
First, a few things NOT to do:
•Don’t cut off any more than 25 percent of a plant’s growth in a single year.
•Don’t “top” trees by shearing off all growth from the tips back. It’ll encourage lots of weak new twiggy growth.
•Don’t use tar, paint or similar wound dressings after pruning. That can encourage rotting and disease.
•Don’t climb up in trees to prune — especially not with a chainsaw in hand! Hire a pro if your bigger trees need work.
•Don’t let plants get so overgrown and out of control that you have to cut off big branches. Big wounds don’t heal as well as small ones.
And now, some do’s:
•Do leave those branch collars intact.
•Do trim hedges so they’re wider at the base than at the top.
•Do try to prune plants so that about half of the total growth is in the lower two-thirds of the plant.
•Do use the right tools. Don’t try to cut big branches with little hand-held pruners. And keep your blades sharp.
•Do step back and look often while you’re pruning. Remember, once you cut a branch off, you can’t glue it back on.
•Do select the right size plants for your site up front. It’ll save you lots of needless pruning later.
If you have further questions, don’t hesitate to contact our nursery or horticultural information staffs. We’ll be glad to help!
When to prune specific woody plants
Clematis (summer blooms)
Inkberry & Japanese hollies
Rose of sharon
St. John’s wort
Clematis (spring blooms)