Planting a tree is always an act of faith. But these days, it feels more like a gamble.
With a changing climate and a parade of pests that threaten trees — Japanese beetles and emerald ash borer, anyone? — choosing a tree is daunting. Minnesota’s weather has grown more unstable, with frequent torrential rains and late-year droughts. Even an insulating snow cover to protect new roots in extremely cold winters is no longer guaranteed.
In this new environment, going with native trees does not guarantee success. Look no further than Nerstrand Big Woods State Park near Faribault, where visitors can walk in the native hardwood forest that once covered much of the state. About 12% of the park’s trees — 200 acres of native oaks, maples, basswood trees and others — have died recently because their roots are suffocating in over-wet soils.
Lee Frelich, director of the University of Minnesota’s Center for Forest Ecology, told Master Gardeners at a meeting this summer that as the world warms, Minnesota’s climate will soon mirror that of current-day Nebraska and Kansas. Tree ranges will shift northward by about 300 miles. Minnesota’s beloved North Woods will change forever; maples and oak eventually will overtake cold-loving spruces and firs.
So, what’s a tree lover to do? Before planting a tree, do your research and consider your site. This University of Minnesota Extension website will help: extension.umn.edu/forestry/tree-selection-and-care.
For those who want an imposing tree, 40 feet or taller at maturity, U experts say these trees should thrive in a changing climate: black cherry, black walnut, bur oak, chestnut oak, eastern red cedar, hackberry, jack pine, Kentucky coffee tree, northern catalpa, northern white cedar, ponderosa pine, Prairie Expedition elm, red maple, river birch, shingle oak, Siouxland poplar, tulip tree, white pine and London plane tree.
Smaller trees that should do well include Black Hills spruce, blue beech, chestnut crabapple, ironwood, pagoda dogwood, serviceberry, amur maackia and Katsura tree.
In the past, some of these trees have been borderline hardy in the Twin Cities’ horticultural Zone 4. London plane tree, a towering hybrid of American sycamore and Asian plane tree with exfoliating gray and beige bark, has long been a landscape stable in European cities. Though it traditionally has been a Zone 5 plant, Minneapolis has added it as a boulevard tree. Adaptable to a wide range of soils, it needs full sun and room to grow more than 75 feet high.
Another good big tree that makes a landscape statement is Kentucky coffee tree. Despite the name, this tree is a native that can top 60 feet. Slow-growing at first, Kentucky coffee tree has an elm-like grandeur at maturity. It is one of the very few trees with no serious pest or disease problems.
Should you want an American elm, new varieties have resistance to Dutch elm disease. St. Croix elm was discovered in Afton, and Princeton, New Harmony and Prairie Expedition are available in local nurseries. Smaller hybrid Asian elms with disease resistance are tough trees that U experts say will grow where other trees struggle. Varieties available locally include Accolade, Cathedral, Discovery and Triumph.
If you want an elm, it’s worth talking to nurseries about the recommended care of the young trees. Some varieties, especially American elms, need expert pruning when young to develop proper form when big. Also, plant these newer elms at least 65 to 70 feet apart. These trees are resistant to Dutch elm disease, not immune from it, and giving them lots of space ensures that if one tree gets sick it won’t spread the disease underground to another elm through grafted roots.
Though maples are struggling around Minnesota because of salt damage, girdling roots and poorly drained soils, people still love them for their brilliant fall color. If you choose a maple, look at the U Extension web page for instructions on how to plant it correctly. Planting maples too deep has been a death sentence for many trees, though they may linger for years before finally dying.
Less-used trees with red fall color include northern pin oaks, black gum trees and the U-developed buckeye Autumn Splendor.
For a smaller tree, look at serviceberries and pagoda dogwood. Serviceberries are natives that are visually interesting all year long, with white flowers in the spring, yellow or red fall color and berries that attract wildlife and can be used for jellies and jams. As trees, they can reach 25 feet high or they can be trained into a shrub form. Hybrids are available, including the shorter Regent and taller Autumn Brilliance, Rainbow Pillar and Standing Ovation.
Pagoda dogwood is another native that can grow to about 25 feet as a tree or can be used as a shorter shrub. It has fragrant white flowers in spring, berries that attract birds and purple or red leaves in fall. It prefers partial shade; most varieties can take only about six hours of direct sun.
There are many other options, so go to the extension website and investigate. While it’s easy to despair and feel powerless about global warming, adding trees to our landscape is one thing we can do to combat a warming Earth. The world needs trees now more than ever. Plant one.
Mary Jane Smetanka is a Minneapolis freelance writer and a Minnesota Tree Care Advisor.