How to grow your own champion tree
Wheaties might be the breakfast of champions, but it's hardly the secret formula behind our region's champion trees. Recent news reports have featured several of the region's largest trees, termed champions on official registries kept by forestry departments in North Dakota, South Dakota and Minnesota. How can we get the trees in our yards to grow like that: large and long-lived?
North Dakota's largest tree is a huge cottonwood located in a pasture near Portland that is 105 feet tall with a canopy spread of 92 feet and a 30-foot circumference. Minnesota's largest tree is a 33-foot circumference cottonwood near Watson.
The largest trees aren't necessarily the oldest, as some species grow larger at a younger age. For example, North Dakota's largest cottonwood is estimated to be about 200 years old. But trunk core borings of living bur oak trees in North Dakota have found individuals more than 450 years old, even though they might not be the largest size. Oaks grow medium-slow, but have very long lifespans.
How long can a tree live?
Theoretically they can live forever, as there's no built-in kill switch. But practically, trees live until something goes wrong. Although most trees coexist fine with a few insects and leaf diseases, some pests do kill trees. Often trees are first weakened by other forces like drought, human activity or herbicides, and then secondary invaders finish them off. As a general rule of thumb, slower-growing tree species tend to be stronger and longer-lived.
What can we do to help our trees live long, healthy lives?
Tree care can be separated into do's and don'ts. Because more homeyard trees are killed by human activity than insects and diseases, the don'ts have the greatest impact.
Don'ts of tree care
- Don't harm trees with improper use of lawn weed killers. Herbicides that kill broadleaf lawn weeds can also kill trees, and it's usually sneaky instead of a direct kill. University of Nebraska researchers indicate that if you can smell the chemical in the air after spraying, area trees are likely being damaged from airborne molecules as leaves also 'smell' and absorb the chemical.
- Trees are especially affected if exposed to lawn herbicide misuse year after year. Growth slows, the leafy canopy thins and the tree's system becomes depressed as its internal energy decreases. Lawn herbicide misuse in this slow decline often goes undiagnosed.
- Lawn herbicides containing the active ingredient dicamba are especially dangerous to trees. Dicamba moves downward in the soil, entering the tree's roots, where the poison is taken internally into the tree. Tree roots occupy a wider lateral spread than most of us might imagine. Roots spread outward from the trunk at least one-and-one-half the tree's height. An average 40-foot high tree has roots extending at least 60 feet from the trunk in all directions. The lateral root system extends out beyond the tree's leafy canopy about two to three times the canopy's area. If a yard has trees, most of the lawn is underlain with a network of roots. If dicamba is sprayed on the grass over this root network, trees can suffer lasting damage.
- Nicking the trunk's bark with lawnmowers and string trimmers might seem harmless, but it causes serious problems. The tree's lifeblood cambium is a very thin layer directly under the outer bark. Scarring tree bark can easily damage the cambium, which is the tree's life-supporting growth area. Damage is cumulative, and over time a tree can become weaker, thinner canopied and less vigorous, easily shortening its life.
- Insects and diseases often prey on weakened trees whose resistance is diminished after years of exposure to lawn chemicals and bark injury. Avoiding misuse of lawn chemicals and being cautious when mowing and trimming can help a tree remain healthy and better able to win insect and disease battles.
- Don't overwater trees, especially when watering lawns with sprinkler systems. Soggy soil can quickly kill many tree species.
Do's of tree care
- Use lawn weed sprays carefully, avoiding dicamba on lawns where trees are present. Examine product active ingredients. Check labels for amine forms of 2,4-D, which are safer than the more volatile ester forms.
- Apply tree wrap protectors around the trunks of young and thin-barked trees every fall to prevent winter sunscald injury and animal damage, and remove in spring.
- Growth can be enhanced by applying well-balanced tree and shrub fertilizer in the spring. Don't fertilize after July 4, as late-stimulated, tender growth can winterkill.
- Water established trees deeply, and less often. A good soaking every few weeks is plenty in the absence of rain.
- Mulch around trees with a circular layer of wood products 5 feet in diameter, 5 inches thick, and kept 5 inches away from the trunk.
A list of North Dakota's champion trees can be found here.
Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler's Greenhouse in Fargo. Readers can reach him at firstname.lastname@example.org.
He also blogs at growingtogether.areavoices.com.