When pruning, check whether a branch is alive by looking for a layer of green, living cells under the bark. It will show if you scrape the bark, left, and as a green ring in a cut branch, center. Deadwood, right, shows no green. (Morton Arboretum )
The first step in pruning a shrub or tree is to remove branches that are dead.
“Any plant will accumulate a certain amount of deadwood over time, due to harsh weather, disease and competition,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “If you clear the deadwood away first, it will be easier to see which live branches you might want to remove.”
Pruning out deadwood also opens up the interior of a shrub to allow more light in and to improve air circulation, which reduces the chances of disease.
There’s just one difficulty: It’s not always easy to tell dead branches from live ones, especially in winter, when the living branches don’t have leaves.
Here are some suggestions from Yiesla for making sure that what you prune is deadwood.
Look closely. Splits, cracks or holes may make it obvious a branch is dead.
Bend a small twig. When wood dies, it dries out, so a dead twig will be brittle. It may break cleanly or feel too hard to break. A live twig will feel more flexible and will bend before it breaks. “The difference will be more apparent when it’s not too cold,” Yiesla said. “Even live wood gets brittle when the temperature is in the teens or colder. But when it’s that cold, it’s probably not the best day to be outdoors pruning anyway.”
Check for green. A live branch, even on a dormant tree or shrub, will have a green layer of living cells underneath the bark. If you cut through a branch and look at the end, you can see it as a thin green circle. To check for this living layer without cutting through the branch, use your fingernail or the back edge of your pruner’s blade to scrap a nick in the bark. “If you see green, it’s alive,” Yiesla said. A small nick will gradually seal over with bark when the growing season starts.
Consider the location. Slender, new twigs are most vulnerable and most likely to die off. “If you find dead twigs, it doesn’t mean that the whole branch is dead,” Yiesla said. “Remove the twigs and then work down the branch gradually until you find live wood.” However, if you can tell a main branch is dead, remove the whole thing; all its twigs will be deadwood too.
Examine the bark. Often, the bark of a dead branch will be darker than that of nearby live branches. The difference may be subtle, and it can vary by species.
Feel when you prune. Deadwood is harder, so you will feel more resistance when you cut through a dead branch with your pruners.
Watch for decay. Deadwood that has started to decay may feel soft when you poke it. However, patches of gray or green lichen or moss on the bark don’t necessarily indicate deadwood. “They can also grow on the bark of living branches, so use other methods to make sure the wood is dead,” Yiesla said.
Don’t worry if you guess wrong. “Even if you accidentally cut off a live branch or two, the shrub will recover,” Yiesla said. “With experience, you’ll get better at telling live wood from deadwood.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (mortonarb.org/plantadvice
or plantclinic@mortonarb.org
). Beth Botts is a staff writer at the Arboretum.
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