We continue last week's Mystery of the Murdered Trees.

Our investigative reporting is less interested in revealing whodunit than in stopping the carnage inflicted by mowers, trimmers, tree wraps and planting too deep.

These man-made problems are injuring more young trees in our new developments than disease, insects and winterkill.

Mower, trimmer damage

The solution is straightforward: Stop it!

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Let's treat a tree trunk as we would the leg of a prized quarter horse, which we wouldn't risk bloodying by approaching closely with a string trimmer or bruising with a lawn mower.

The best defense is a circle of shredded bark or wood chip mulch around the tree in a 2- to 3-foot diameter circle about 3 inches thick.

Caution: Don't apply the mulch next to the tree trunk, which can cause a whole new set of problems. The mulch ring should surround the tree like a doughnut-shape, with the tree trunk inside the doughnut hole.

Tree wrap damage

I discovered severely damaged bark concealed inside tree wraps on numerous young trees. The injury occurs from bark constriction and abnormally moist conditions favoring rot and insects when tree wraps are left on too long.

The solution is simple. Remove the smaller diameter white tree wraps after the first year. The black larger-diameter, tubular tree wraps can remain longer if there is always an inch or two of free space around the trunk. Under no circumstance should tree wraps be left on until trunk contact occurs.

Consider removing tree wraps during the summer growth season and replacing it loosely in fall to protect the trunk from winter animal injury and sunscald damage.

Tree planting depth

It is a common horticultural practice to plant items just a little deeper than in the previous container.

For example, we bury tomato plants deeply because they root along the stem, producing a stronger plant.

But some plants like African Violets, strawberries, peonies and trees have definite "crowns" that resent being covered deeply with soil.

Don't roots just keep growing deeper anyway, so what's the big deal if they are planted a little deeper to begin with?

Understanding tree roots is enlightening. It's easy to mistakenly think of roots as a large mass extending deeply into the earth on their way to China.

Instead, did you know that more 70 percent of a tree's roots are in the upper 2 feet of soil, and nearly 95 percent are in the upper three to four feet? Roots of most species spread outward in this somewhat shallow layer. (Walnut and oak are exceptions.)

Tree roots aren't stupid. The roots would rather hang out for food, drink and oxygen in rich, nutritious topsoil. If we bury the root system deeply, we are thwarting the tree's natural desire.

Knowing whether a tree is planted to deeply requires a little snooping into the soil next to the tree trunk to find the "root flare," which is the widened point at which the large support roots branch from the trunk. Picture walking in the woods and stumbling over the roots that are adjacent to the tree trunk.

If covered too deeply, the root flare won't be visible. If the trunk goes into the soil as straight as a telephone pole, be suspicious.

Use a sharp, pointed object such as a screw driver or awl to carefully excavate the soil next to the trunk until you locate the support roots. These roots are supposed to be at or slightly above the surrounding soil grade.

If this is a potted tree for a new planting, gently remove excess soil if too much is on top of the support roots. Remember to slice into the sides of the rootball about an inch to sever circling roots which create problems.

If you determine that an older, existing tree has been planted too deeply, we have a problem. It may grow for a while but begin a slow decline that can take up to 10 years to become evident.

The symptoms of this decline include lack of vigor, slow growth, increased susceptibility to bark splitting and frost cracks, trunk wounds, dead branches or tips, thinning leaf canopy, and attack by secondary insects and diseases.

For an established tree, there is no good solution. Give the tree good care, water during dry periods, fertilize in spring, and prune out dead branches. At this point holy water and a priest's blessing might be appropriate.

Our new city developments need trees to grow at optimum rates. We can't afford to lose trees needlessly at a young age.

For a good example of proper young tree planting and maintenance, observe boulevard plantings by the City of Fargo Forestry Department. City Forester Scott Liudahl and crew are doing a nice job.

Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler's Greenhouse in Fargo. Readers can reach him at donkinzler@msn.com.