Minnesotans love their maple trees. Maples make up more than 20 percent of the trees in the state. With their bright fall color, fast growth and dense canopies that shade house and yard, what's not to like?
But as our climate changes and new invasive tree-eating insects march toward Minnesota, it might be time to look at alternatives if you're planning to add a tree to your yard next growing season.
Some maples already are struggling in Minnesota, for reasons that aren't entirely clear. When I was answering questions last year at the State Fair's Minnesota Tree Care Advocate booth, one of the most common was, "What's wrong with my maple?" People described trees that should have been in their prime that were dropping branches, not leafing out and showing increasing dieback in the canopy.
While some of this could be linked to improper planting or drought, experts at the University of Minnesota say it's time to break our reliance on maples. If we keep planting maples and a new disease or insect arrives, we could end up with the situation we already face with ash trees. Ashes, Minnesota's third-most popular tree, are expected to be decimated by the emerald ash borer.
Maples are a favorite of Asian long-horned beetles, an exotic pest that moved from the East Coast as far west as Chicago before an intense decadelong effort to eliminate the pest in Illinois beat the bug back to Ohio. The beetle has no natural enemies in this country, and some experts say it has the potential to do more damage than Dutch elm disease, chestnut blight and gypsy moths combined.
So it's a good time to make our urban forest more diverse. The job may be even more urgent in cities: in Minneapolis, a 2005 tree count shows that more than 28 percent of the city's trees are maples.
Here's some options to consider:
Among big trees, the handsome Kentucky coffee tree is underused here. Reaching 50 to 70 feet tall, it's a great statement tree to replace big elms, ashes and silver maples. Look for male cultivars like "Espresso" that have no seed pods; the University of Minnesota has a similar introduction called "Stately Manor" that may be hard to find in nurseries.
Kentucky coffee tree is tough, tolerating compacted soils, alkaline areas and drought. It's a wonderful tree for urban homeowners who have the room for an impressive feature in their yard.
Some of us have never gotten over the loss of elms to Dutch elm disease. In my neighborhood, a few of these enormous trees still grow along boulevards, the soaring arches of their branches almost joining to form a leafy tunnel over streets. Elms are fast-growing, hardy trees that tolerate city conditions. Now homeowners can buy varieties that are resistant to Dutch elm disease. Among them are Patriot and a new variety discovered in Minnesota called St. Croix. Both of these trees have the classic, vase-shaped growth habit that elm lovers crave. St. Croix is expected to be more widely available in nurseries this year.
A smaller tree that tolerates urban conditions is buckeye. I've seen a lot of these planted as replacement boulevard trees and have been impressed by their handsome, rounded shape and yellow spring flowers that look a bit like bunches of orchids. The variety "Autumn Splendor," a U of M introduction, reaches about 35 feet high. Leaves are a deep red to maroon in the fall. Extremely picky homeowners may not care for the tree's seeds, but for me the tree's attributes outweigh any criticism that it is messy.
Lindens are shapely, upright trees with yellow spring flowers that attract bees. Ranging from about 30 to 50 feet in height, these handsome trees often have an almost pyramidal growing habit. Know that lindens are a favorite of Japanese beetles.
Hackberry is another tough tree with distinctive warty-looking gray bark. This fast-growing tree reaches 40 to 60 feet tall and has yellow fall color. Birds like the fruit. It tolerates almost any growing condition.
Among smaller trees, newer varieties of crabapple are showy, with disease resistance that keeps them looking good right into fall. Many of these newer varieties have persistent fruit that remains on the tree. "Prairiefire" has leaves that emerge purple in the spring before turning green, hot-pink flowers and maroon fruit. Other disease-resistant varieties with persistent fruit include "Donald Wyman," with white flowers and red fruit; "Harvest Gold," with white flowers and gold fruit; and "Professor Sprenger," with white flowers and orange-red fruits.
Lastly, don't forget a small tree that is usually overlooked until it flowers in spring and everyone begins asking what it is. Japanese tree lilac ended up on a Master Gardener list of tough plants for tough sites for good reason. I've seen it persist and flower in cramped planting boxes along parking lots in downtown Minneapolis and thrive in plantings along hot, dusty Hwy. 77.
Japanese tree lilac reaches about 25 feet, has dark green leaves and is in its glory in late May and June, when it produces showy cream or white flowers. If you're sensitive to flowery scents, it may not be for you. But it attracts butterflies, and deer don't seem to care for it. Properly cared for, this workhorse of urban landscaping can be a showy addition to your yard.
For more information, the University of Minnesota has a page with information on trees for all different parts of the state. Check it out: (myminnesotawoods.umn.edu/2008/11/recommended-trees-for-minnesota-by-region/)
Mary Jane Smetanka is a Minneapolis freelance writer and a Master Gardener.
