Plant a ‘safe’ tree to avoid trouble down the road

By Bev Johnson | The Daily Journal

Published Saturday, November 17, 2007

The University of Minnesota Department of Forest Resources continues to stress proper tree planting. The concern is that ten years after you have planted a tree the wrong way, a strong wind will knock it over and smuck your car.

The problem with improper planting is stem-girdling roots. The roots actually slowly kill a tree. Little Leaf Lindens seem to be the most prone to this injury.

Gary Johnson, Forest Resources, describes the problem like this: "Imagine blowing up a long skinny balloon. Now squeeze the middle of the balloon. Note that the diameter above and below is significantly larger than the area that is being squeezed, a.k.a. girdled."

In a windstorm, this compressed point is quite literally the "weakest link in the chain," and is the point where the tree will break off under the loading pressure of the wind.

The University of Minnesota conducted studies from 1994 to 1996 in urban tree decline.

Of the 220 declining and dying trees that were

diagnosed, 80 percent had stem girdling roots, and were the "only causal agents isolated from the 'patients.’

These trees had been planted from 12 to 20 years earlier and had more than 50 percent of stem compression. In all these cases, the SGRs were well below ground, from four to 14 inches in the soil.

Later studies demonstrated that the deeper the tree stems were in the soil or mulch, the more likely they were to have multiple layers of the killing roots.

Most people were not too impressed with the idea that a tree died after 12 to 20 years as many felt that 30 years is a normal life span for a tree. Actually, urban landscape trees, whether planted in a sidewalk pit or in a landscaped yard, live only seven to 35 years.

The normal life for a boxelder, cousin of the maples, is about 100 years. Many of our native trees should live well into their 90s.

So, how often do trees die from strangulation of their roots? Who knows. When a tree falls during a windstorm, we don't as a rule dig up the roots for a look.

However, the University did just that. The Tree Failure in Wind Storms research did 1,500 "tree autopsies" from 1995 through 2005.

These weren't trees that fell during tornadoes or severe straight-line winds but winds during thunderstorms or winds at the edges of severe wind events.

So how do you, the homeowner, prevent trees from taking out your car or roof? When you get a potted tree, dump it out of the pot and shake the soil off the roots.

Cut off any circling roots, then plant the tree with the top root only 1 to 2 inches below the soil. Mulch, but keep the mulch 2 to 3 inches, at least, from the trunk of the tree.

Now you should have a tree that will outlive you, so be sure you put it in the right spot the first time. Remember, it will not only get taller, but wider, too.