Winter Tree Tips from The Morton Arboretum: Prune your trees when leaves are off to see the overall form and detect problem areas. Trees pruned in winter will lose less sap and may be better able to resist strong winds and snow loads.
Why Prune in Winter?
Chicago winters are challenging for us – and our trees. Vicious wind and ice storms can break weakened tree branches and send them hurling at homes, cars or people. During winter, when leaves are down, you can really see a tree’s structure and form, and any dead or undesirable branches – as well as cracks or broken stubs from previous storms.
Some of the reasons you may want to prune include:
- to remove dead, diseased or damaged branches
- to reduce overall branch density and allow new growth
- to improve air circulation and wind resistance
- to reduce the height or width of a tree
- to remove lower branches that hang too low or block sunlight
- to remove branches that touch the house or other structures
- to improve a tree’s overall shape and growth habit
- to get some fresh air and exercise!
Tips for Successful Winter Pruning
Depending on the size of the tree, it may be wise for you to call a certified professional arborist to inspect for inherent structural problems. Climbing a ladder in winter may be dangerous – especially when carrying a pole saw, pruning saw, shears or loppers. Remember, safety first! Some jobs are better left to professionals.
When doing the work yourself, choose a dry, sunny day with no (or low) winds. Make as many pruning cuts as you can while standing on the ground, in order to limit your time on the ladder. Be sure to wear safety goggles, as sawdust or worse – falling branches – may injure your eyes. Wear layers of durable clothing, appropriate for the temperature and weather conditions, including protective gloves and boots with good slip-resistant treads.
When removing larger branches, you may want to tie them to limbs above, and lower them to the ground after cutting – to prevent damage to objects below. And most important – use a sturdy ladder that is firmly placed on the ground (avoid ice) and ideally, held sturdy by an assistant on the ground.
Even though tree sap is not flowing as much as it is during non-winter months, tree diseases can still be spread from tree to tree by infected tools. After pruning each tree, remember to disinfect your pruning blades with a solution of 1 part bleach to 9 parts water, followed by a quick cleaning with soapy water, then drying with an old towel.
What to Prune
First, remove dead, diseased, damaged, crossing or rubbing branches. Then attend to the trees’ form. Trees should develop a straight central leader, along with well-spaced branches and a generally symmetrical crown, depending on the species. Here, prevention is the best medicine. Young trees need pruning to help give them a good start. If young trees aren’t pruned well, structural problems become more pronounced and difficult to correct as trees mature.
Small branches may be removed with pruning shears, clipped close to (but not including) the branch collar.
For example, if the central leader is cut or broken off, two or more leaders may form. Instead of an “I” shape, the tree grows into a less-stable “Y” shape. When the tree is young, it is possible to tie and train a side branch to replace the broken leader. But if a mature tree loses its leader, it’s almost impossible to restore good structure. For this reason, never “top” a tree by lopping off the central leader (as is often done under power lines).
Another common structural problem to look for is a weak branch union, where two main limbs join the trunk. Look for places where two branches are growing so closely that bark has developed inside the union – which is often too weak to hold the limbs together and may split or crack down the middle.
Trees that have an upright habit, with branches that connect to the central leader at less than a 45-degree angle, may be particularly prone to weak branch unions. ’Bradford’ pears (and other callery pears) are especially susceptible to this problem. To remedy, you might remove or shorten one of the limbs, or in the case of a mature tree, hire an arborist to insert a bolt to hold the union together.
How to Prune
Whether you are pruning during winter, or any time of year, you should follow this three-step process when removing large branches:
Step 1: Begin on the underside of the branch at least one foot away from the trunk or branch collar, cutting upward approximately one-third of the way through the branch.
Step 2: Cut the topside of the branch, directly above your first cut, cutting all the way through the branch. This method eliminates most of the weight that would cause the falling branch to tear away parts of the main limb or trunk.
Step 3: In the final step, go back and safely remove the branch stub outside of the branch collar (the ridges that cause a slight bulge where the branch attaches to the tree).
Some Common Questions about Tree Pruning
Q: I have heard tree paints are not really necessary. Is this true?
A: Research tests have concluded that wound dressings had no affect on the rate of preventing disease. In most cases, pruning cuts will close by a natural callus without any aid. The exception would be pruning oaks and elms in the summer. The potential for spreading oak wilt and Dutch elm disease are greater when insects are active.
Q: Last year I pruned a broken maple branch in February and the sap ran for three weeks. Is there something I should have done?
A: Maple, birch, elm, walnut, and a few other trees are considered “heavy bleeders.” Although unsightly, it is harmless and can be avoided by delaying the pruning of these trees until the foliage has emerged in late spring.
Q: What tools are necessary for pruning?
A: Help your plants heal quickly by choosing tools with sharp, clean blades. Dull blades can tear or rip the bark causing a wound that will not heal properly. Hand pruners (bypass-type blades are best) are appropriate to cut smaller branches up to 1-inch in diameter. Loppers have longer handles allowing for greater leverage, and will cut branches ¾ inch to 2 inches in diameter. Use a pruning saw for cutting branches 1-inch or larger. A folding saw is handy; it’s safe to carry and works anytime a hand pruner, lopper, or hedge shear won’t do. A pole saw is helpful for reaching high branches, but both the blade and the extended pole should be secured tightly. ALWAYS wear gloves and goggles when working with tree pruning tools!
Know When to Ask for Help
Mature trees may not show signs of internal decay but if left undetected, large branches or the entire tree may blow over in a storm. Take preventative measures by having an arborist inspect your mature trees on a periodic basis.
Certified professional arborists are trained climbers and can detect internal decay and other potentially hazardous conditions.
In some cases, a mature tree may be hollow or so hazardous that it must be taken down. In an otherwise healthy tree, if large hollow limbs are detected, an arborist may prune them back and then run cables from the trunk to the limbs to reduce the chance of breakage. Arborists may also recommend installing lightning protection on tall trees. In general, such techniques are only warranted if the trees are healthy or valued specimens.
More Winter Tips for Healthy Trees
In addition to proper pruning, you should make sure that trees are properly mulched and watered going into winter (see Fall Tree Tips). If you have potted trees such as small evergreens, be sure to water (although minimally) when the soil is dry from lack of snow cover. You should also protect your trees from winter winds and road salt, and from browsing animals and rodents that may damage bark.
For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or email plantclinic@mortonarb.org
For more tree-related tips and information, go to the Morton Arboretum plant advice web page.
These links may be especially helpful: