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Once again, I've come across a warning that the most common cause of tree loss in home landscapes is planting too deep.

A fairly recent phenomenon beyond our control is affecting not only ornamental flowering and shade trees but also backyard fruit trees.

The problem has arisen from a surprising source -- commercial growers with field plantings -- even before trees go into nursery cans and are shipped to retailers and garden centers.

This very convenient system has a weak link.

During the first 2 or more years growers nurture trees in the ground, repetitive plowing between rows pushes soil to the side. As it accumulates over roots and around the lower tree stem or trunk, thin adventitious rootlets sprout. When trees are eventually dug up and set in cans, this excess soil goes along and these rootlets look like the real thing.

In too many cases, the soil rises 1 to 2 inches above the crown -- that sensitive point where roots differentiate from stem tissue. Thin rootlets in this topped-off soil are not true roots, but most home gardeners don't recognize this and add even more soil over them when planting. In time, fungal activity rots the crown area and trees die.

If you've planted trees in the past -- any type of tree of any age -- it pays to examine the base of the trunk. If you don't observe even a slight flare at the base, remove enough soil until you do.

Without damaging bark, remove soil around the trunk until you reach roots at least the thickness of a pencil. Then, leave this area exposed -- where the trunk begins to flare out, only slightly on very young trees, more dramatically on older ones.

When planting a new tree, locate the true roots and dig a hole no deeper than the true depth of the root ball so that it sits on solid ground and will not settle.

The hole should be twice as wide as deep, then filled with native soil and no amendments.

Trees planted too deep may live for 10 years or more, which may seem like a long time, but for most trees, it's a brief life span with a slow decline.

Risky features

Of the lessons I learned in the very first garden class I took, I remember the instructor saying: "People come into my nursery for a tree to plant today but want to hang a hammock on it in 6 weeks."

The point, of course, was to emphasize that trees take time to reach the ideal size we have in mind when we first decide to plant.

As it happens, when trees -- and other woody plants -- develop height quickly, they often have a weak structure and bend so easily that they break in the wind.

Bradford pear (Prunus calleryana), one of the most commonly planted, fast-growing landscape trees, succumbs frequently to breakage from weak crotches and narrow limb attachment.

Eucalyptus is legendary for succumbing to wind damage and creating messy debris.

Other shortcomings

Several other fast-growers come with drawbacks. Summer-blooming mimosa (Albizia) is also brittle, deciduous until nearly June, and messy for another 6 months as it drops blossoms and seed pods.

Empress tree (Paulownia) develops a tall, 10- to 20-foot single trunk from seed its first year, slowly puts out branches, dazzles with long purple flower panicles, and annoys by dropping messes for months.

Spectacular purple blossom clusters on jacaranda are also tempting and while it doesn't have weak wood, it struggles in our cold winters.

Birches (Betula), native to moist, humid climates, are short-lived here and should never be planted in our Mediterranean climate. Alders (Alnus) and liquid amber (Liquidambar) are so shallow rooted that nothing grows easily under them.

Selecting a tree

Despite the shortcomings of some attractive trees, lists are long for pleasing, problem-free species, though none is perfect in every way.

For a large shade tree, instead of sycamore (Platanus), which suffers leaf drop from fungal infection in moist spring weather, opt instead for similar tulip tree (Liriodendron), a fairly fast grower that stays strong.

Although most maples do best in moist, humid climates, a few species adapt to our dry summers.

Trident maple (Acer buergerianum) and amur maple (A. tataricum ssp. ginnala) stay below 20 feet for many years while red maple (A. rubrum) grows somewhat taller.

For more suggestions, visit sonomamastergardeners.org and click on Top Plants for Sonoma County.

(Rosemary McCreary, a Sonoma County gardener, gardening teacher and author, writes the monthly Homegrown column for The Press Democrat. Write to her at P.O. Box 910, Santa Rosa, 95402; or send fax to 664-9476.)