by Katie Himanga, Heartwood Forestry
Winter is such a great time of year to prune most trees. It has many advantages over summer pruning.
Most of the economic and risk management benefits of winter pruning come from removing defective tree branches and dealing with defective forks on tree trunks: dead, cracked or broken branches; branch union with included bark and other structural problems. Too often, tree owners delay pruning until a tree looks unsightly. Then they prune for appearance. The result may be a tree that looks okay, but is full of defects that set the stage for storm damage and premature death. Even worse is the old technique of topping trees, which leads to trees full of defects and decay. Prune trees for safety and tree health first. Consider appearance after that.
Before you prune for appearance, consider:
HOW TO PRUNE
Before you prune, inspect your tree from the top down and plan the work. Remember tree safety and health come before appearance. Make pruning cuts with respect for the natural defense system of the tree. Make cuts at branch unions. Leave branch collars. Use sharp tools and make smooth cuts. There should not be any loose bark around the cut. If a branch is too big to hold in your hand, use three cuts to remove it. When you must cut the main part of a branch back to a side branch, the side branch should be large enough to become the new leader. Select a side branch that is one third or more the diameter of the branch that you must cut off.
Learn to tell the difference between a strong branch union and one that is weak. A strong union is U- shaped and has a ridge of branch bark running through it. A weak branch attachment has a narrow, V-shaped union and bark turns into the union and is trapped between the branches. Never damage a branch collar with a pruning cut.
Plan which branches to remove so your tree develops well-spaced side branches. For a strong tree, the side branches should be less than one half the width of the main trunk.
WHEN TO PRUNE
Start winter pruning in November and finish by April 15. Avoid pruning live wood from trees when leaves are forming or falling. During these times, the tree is busy either putting on spring wood and new leaves or storing starch and putting on new roots. Less energy is available to respond to pruning wounds than at other times of year. There is no need to cover tree wounds with wound dressing during winter pruning operations. In the spring, sap will flow from late-winter pruning wounds on a maple or a birch. It is not harmful to the tree.
Begin pruning a young tree the first winter after planting. Prune sparingly if last season's twig growth was less than 4" in length. The tree needs more time to recover from the shock of transplanting. Once the tree recovers vigor, focus on removing defective tree parts so little problems don't grow into big problems. Removing one limb of a defective fork on the tree trunk may mean the difference between a tree that splits in two the first time the wind gusts more than 60 m.p.h. and a tree that stands up to the elements for decades.
Removing dead and damaged branches are all that is usually needed for a mature tree that has had regular care throughout its life.
PRUNING A YOUNG TREE
PRUNING A MIDDLE-AGED TREE
PRUNING A STORM- DAMAGED TREE
To estimate the number of trees you need to prune each year, take the total number of trees under your jurisdiction that are more than five years old and divide by five. Add to that the number of trees that are up to five years old. If well-maintained trees is your goal, plan to prune at least that many trees each year.
As is true in other professions, the field of arboriculture has industry standards or standards of practice. Standards help clients and arborists communicate on what work is to be accomplished during a tree-care operation. Anyone who writes tree maintenance specifications should be familiar with Standard Practices for Trees, Shrub and Other Woody Plant Maintenance, ANSI A300. It is available from the American National Standards Institute or from the National Arborist Association. ANSI A300 defines general categories, or types, of pruning. If you hire a tree service company, you can specify which type of pruning best fits your budget and your needs. In addition to the type of pruning, you must specify the minimum and maximum size branches to remove. The ISA booklet Tree Pruning Guidelines complements ANSI A300. The standards tell what to do; the guidelines explain how to do it. For people who don't work with trees every day, the guidelines are easier to understand.
Ask any arborist you plan to hire if he or she is "ISA Certified." Certified Arborists carry an International Society of Arboriculture (ISA) Certification Identification Card. To become certified, an individual with at least three years of tree-care experience must pass an examination. To stay certified, the arborist completes 30 hours of continuing education every three years. ISA certification is a good indication of knowledge about tree care, but it is not a guarantee of quality work.
Katie Himanga is a consulting forester and owner of Heartwood Forestry, Lake City, MN. Among other things, she teaches tree pruning and line clearing in Minnesota, Wisconsin and North Dakota and is an I.S.A. Certified Arborist.
Parts of this article are extracted from Tree Trust Community Outreach Manual, 1996. Used with permission. To purchase this manual, contact Tree Trust at 612-920-9326.