George Weigel is a garden writer for The Patriot-News in Harrisburg, Pa., and also a garden designer, consultant, speaker, garden tour leader, Pennsylvania Certified Horticulturist and certified gardening nut. When he’s not doing any of that, he battles the groundhogs in his Cumberland County backyard.
 

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Bad Storms, Better Trees
by George Weigel - posted 04/09/12  

Last year, 2011, was a bad year to be a tree.

Tornadoes, borers, diseases, monsoon-like rains and a pre-Halloween snow storm tag-teamed to blow down, rot out and crack apart untold thousands of landscape trees throughout the East and Midwest.

That puts many a tree-less homeowner in the market for replacements this spring.

Two bright sides:
1. This is a great opportunity to increase diversity and plant better-performing species, and
2. We shouldn’t have to worry about any mulch shortage for awhile.

Future storm-related tree trouble can be reduced greatly by better selection, better siting and especially better planting and care practices.

Most of the trees that tore down power lines and fell on houses and streets were bad choices in the first place.

Huge trees aren’t good ideas in small spaces. They’re especially not good ideas in those skinny 3- and 4-foot tree lawns between sidewalks and roads. Besides the concrete and asphalt damage done by growing roots, these trees pose future threats because targets are so close.

Take a look up and out before you replant. Picture your tree as it grows to mature size — not how it looks now. If power lines are above, plant farther away so the mature canopy won’t grow into the lines or topple them should the tree ever fall. Better yet, go with a short species that stays under the height of power lines.

If your yard is just small — especially out front — keep the tree in scale with the space.


Small spaces near walks or roads are best for small trees, such as this pink crabapple.

Some good under 25-foot possibilities for a sunny small space include: crabapple (Malus spp.), crapemyrtle (Lagerstroemia spp.), Japanese tree lilac (Syringa reticulata), snowbell (Styrax japonica), stewartia (Stewartia pseudocamellia), any of the “Little Girl” series of dwarf magnolias, Persian ironwood (Parrotia persica), paperbark maple (Acer griseum) or seven-son flower (Heptacodium miconioides).

Some good choices for a shadier small space include: Kousa, Rutgers hybrid or Cornelian cherry dogwoods (Cornus spp.), redbud (Cercis canadensis), sweetbay magnolia (Magnolia virginiana), serviceberry (Amelanchier spp.), witch hazel (Hamamelis spp.) and American fringetree (Chionanthus virginicus).

A second lesson we learned in 2011 is that not all trees are equally strong. Some species are much more prone to cracking apart in wind and snow load than others. Fast-growing species tend to be the weakest-wooded, and many of those were, in fact, some of the first to fail. Most notorious of the fall-aparters is the ‘Bradford’ pear — a widely planted, white-flowering tree that becomes especially brittle after 12 to 15 years.

Other species prone to breakage are willow (Salix spp.), poplar (Populus spp.), elm (Ulmus spp.), white pine (Pinus strobus), silver and Norway maples (Acer saccharinum and platanoides) and sometimes ash (Fraxinus spp.), hackberry (Celtis occidentalis) and honeylocust (Gleditsia triacanthos).

On the other hand, some species are strong-wooded and sturdily attached. Among the best of the “muscle trees” are ginkgo (Ginkgo biloba), stewartia (Stewartia pseudocamellia), crabapple (Malus spp.), dogwood (Cornus spp.), birch (Betula spp.), oak (Quercus spp.), hornbeam (Carpinus spp.), sweetgum (Liquidambar styraciflua), blackgum (Nyssa sylvatica), hophornbeam (Ostrya virginiana), witch hazel (Hamamelis spp.) and most evergreens.

No matter what you plant, pay attention to the planting site, then pick species that are happy in that kind of spot. Is it hot and sunny? Crabapples and oaks would make more sense than redbuds and dogwoods. Is it damp? River birch and sweetbay magnolia would deal with that much better than firs and beech. Is the soil clayish or compacted? Japanese tree lilacs and ginkgos would tolerate that better than stewartias or flowering cherries.

In other words, do site-specific homework.

The final piece of the safety puzzle is keeping trees healthy. At planting, get the depth right. You should be able to see the base of the trunk slightly flare out just above grade. Otherwise, you may be planting too deeply, which can rot roots and weaken trees prematurely.

Remember, a healthy tree in a happy spot is much less likely to fail than a stressed one.


Korean stewartia is not only a small and strong-limbed tree, it’s beautiful in more than one season.

Once in the ground, these steps will lessen tree failure:

Don’t overfertilize. Most trees need far less fertilizer than people assume. Overdoing it can lead to too-fast growth which can increase the odds of failure.

Prune properly. Good cuts thin out the canopy and reduce the “sail effect” that otherwise increases the wind’s blow-down force. Bad cuts can create weak, excess new growth or wrongly distribute too much weight to the branch ends, which makes a tree more prone to blowing over.

Keep mulch off the bark. About 3 to 4 inches of wood mulch over the roots is fine, but mulch on the trunk can rot the bark and kill a tree.

Don’t cut roots or scalp exposed ones with your lawn mower. Avoid using herbicides around roots, too.

Water deeply once a week in a drought.

Call a certified arborist to have a tree’s health assessed if you notice: a tree leaning; the growth of flat, shelf-like fungal growths on the trunk or roots; dying branches; leaves smaller than they used to be, and any signs of cracking, peeling bark or decay.

Two good sources for more tree-care information are the Arbor Day Foundation at www.arborday.org and the International Society of Arboriculture at www.treesaregood.org.

For help picking the right tree for the right spot, the University of Illinois has an excellent online tool that lets you plug in traits and then kicks out a list of possibilities. It’s at http://urbanext.illinois.edu/treeselector.

 

Photo Credit: George Weigel.

 

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