Unnatural Selection

Paul Hetzler

After a winter fraught with temperature swings, ice and near-record cold such as this past one, being able to finally plant things outdoors is especially welcome. While flowers can be dug up and replanted around the yard much like arranging the lawn furniture, it is different with trees.

Consider that the act of planting a tree is in many ways a transcendent one. Sure, a new tree will give us shade, beauty, energy savings and increased property value, but in most cases it will outlive us by a long shot. In a sense, we donate a tree to the world even when it is on our own property – to future generations of people, to songbirds, to cleaner air, to a better neighborhood.

And once a tree is sited in the landscape, it is not practical, or even possible in many cases, to move it after the first year. For these reasons, it is important to give adequate thought to selection. In an acre of mature forest, nature has selected the few hundred best trees from perhaps as many as 10,000 seedlings. But if we plant one to a few trees, we would like them all to reach their potential. This requires a bit of homework, and is well worth the effort.

A basic question to answer is whether a tree is cold-hardy to your location. The USDA Plant-Hardiness Zone Map is available at https://planthardiness.ars.usda.gov/PHZMWeb/ Don’t assume every tree for sale at a garden center is appropriate for the area. “Big-box” chains may ship the same nursery stock to Raleigh, NC as they do to Potsdam, NY. Check the tag.

Most commonly used landscape trees have one or more cultivated varieties or cultivars, each with its own profile in terms of mature height, branch spread, and tolerance of various site conditions. Make sure your selection can reach full-size without tangling with overhead wires, obscuring a road sign, or encroaching on your neighbors. Some species and cultivars can handle shade, road salt, poor drainage, or disease and pest pressure better than others.

But even when you’ve settled on a candidate with genes well-suited to your site, choice at the individual level is also important. Trees at a nursery or garden center resemble green lollipops from a distance, but checking under the hood can save a lot of trouble later on. A good specimen has a crown like a stoned elephant: it has a single trunk, and is well spaced-out.

Trees having two or more competing (codominant) stems are more vulnerable to splitting as they age. Check the trunk carefully for wounds, removing any trunk wrap if present. A good specimen should be free of crossing and rubbing limbs. Several branches originating close to one another on the trunk will create a focal point for stress, another structural weakness. Ideally the branch placement should have symmetry as the specimen is viewed from all sides, and from above.

It is harder to check out the root system, but if a tree is container-grown, ask the vendor if they would slip off the container to be sure the roots are not excessively pot-bound. Before planting, always tease roots out straight, and locate the trunk flare, which may be hidden under soil in the container or root ball. The planting hole must be at least twice as wide as the roots, and just deep enough so the trunk flare is visible above the soil line when you are done.

Don’t be embarrassed to admit that when you plant a tree, you are leaving a legacy. As such, it is worth the time to select the proper species and cultivar for the site, as well as a specimen having strong, breakage-resistant form. The International Society of Arboriculture has great information on tree selection and planting at: http://www.treesaregood.org/treeowner/choosingtherighttree

Paul Hetzler has been a Certified Arborist with the International Society of Arboriculture since 1996, and is and a member of ISA-Ontario, the Canadian Society of Environmental Biologists, the Canadian Institute of Forestry, and the Society of American Foresters.


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