Wander over to Davenport's Vander Veer Botanical Park and you will see, in the walkway of trees between the conservatory and the Stone Fountain, that several of them are dead or dying.

City arborist Chris Johnson even sawed one off on a recent Friday night because it was "shaking and quaking," and he was afraid it wouldn't last the weekend.

The problem: The trees were planted too deep, which suffocates the roots because they don't get enough oxygen, he said. Without proper roots, the tree falls over.

Jeff Iles, the chairman of the department of horticulture at Iowa State University in Ames, says too-deep planting was identified as a problem as long as 15 years ago, but the correct planting guidelines have apparently not made their way to all of the people who install trees, be they homeowners or landscape professionals.

A rule of thumb is that if you cannot see a flare at the base of the trunk - if the tree goes straight into the ground like a fence post or telephone pole - then it is in too deep.

The reason planting depth has become a problem relatively recently is that until the past couple of decades, most trees were planted "bare root," which made it easy to see the flare and judge the depth, said Duane Gissel, the ISU/Scott County Extension horticulturist.

But as consumers have demanded bigger trees, more are being sold in a container or wrapped in burlap (called "balled-and-burlapped" trees), the flare is often covered and the person planting the tree never sees the roots, he explained.

In other words, the problem starts at the nursery, and unless it is corrected at planting time, it will persist.

"Unless you physically pull back the burlap or soil to find the flare, you could be in trouble," Gissel said.

Many people avoid handling or touching the roots because they fear harming them, and that's a legitimate concern, he says. But handling and even pruning out problem roots is preferable to planting a tree in trouble.

Recommendations from the Morton Arboretum in the Chicago suburb of Lisle, Ill., go even further, saying that if the problem of buried roots is too severe, the tree should be rejected.

Sometimes with a container tree, the person planting it might do what's called "root washing." That is, take the tree out of the container and wash all the soil away, Iles said. That, in effect, makes it a bare root tree.

Girdling roots, bark rot

In addition to suffocation, planting too deep can cause girdling roots.

That's because when a tree is in deep, it will develop what are called adventitious roots - above the original roots - and those can grow around the tree, girdling it, which cuts the flow of water and nutrients. This process can take 20 or 25 years to manifest itself, and by that time a homeowner will be losing a substantial shade tree, Gissel said.

A third problem is that if soil covers up bark, the moisture will cause the bark to rot. A tree without bark is in trouble.

Brian Jay of Davey Tree in Bettendorf said he sees this problem regularly. "I saw it on the last job I just left," he said one day last week. "The tree is struggling and the reason is it was planted too deep. The roots are wrapped around and they are girdling the tree."

So, if you or someone you hired is planting a tree, remember: The root ball should be at or a little above the soil line, and you should not cover it with any more soil, just a thin layer of mulch. And that mulch should be pulled away from the bark, not touching it.

One more thing: Many of today's cultivars have what is called a graft union near the bottom of the trunk, Gissel said. This is the place where the bud of the tree you want - say an Autumn Blaze maple - is joined to the rootstock or trunk of another variety of tree. This allows nurseries to grow desired trees faster than if they simply rooted the bud on its own.

This graft union also causes a slight swelling and should not be mistaken for the root flare, which will be some distance below the union, Gissel explained.