Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
6/3/02
Contacts:
Mark Gleason, Plant Pathology, (515) 294-0579, mgleason@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning June 7
A Few of My Favorite Trees
By Mark Gleason
Extension Plant Pathology Specialist
Iowa State University
When people think about plant pathologists, if they think about them
at all, their reactions are mixed at best. Like cops, doctors, dentists
and lawyers, trouble is our business. No problem for you, no work for
us.
It’s hard to separate the cop from the parking ticket she just gave
you, the dentist from the ordeal of your last root canal or the plant
pathologist from the dismal news about your ailing tree.
"Warm up the chipper" is hardly the verdict you want to hear
for a prized landscape tree that shades your house and beautifies your
yard.But often, the only diagnosis plant pathologists can give is the
final one.
Plant pathologists often play the role of the broom-and-shovel crew at
the end of a circus parade: cleaning up mistakes that were made some time
ago. The classic and way-too-common mistake is planting a tree species
that’s not well adapted to Iowa’s challenging environment.
After 17 years of sweeping and shoveling Iowa landscapes, I’ve developed
affection for the trees that don’t need my help. Here’s a sample
of some of the most reliable, adaptable, durable and problem-free trees
for Iowa.
My Favorites
White pine (Pinus strobus) is the only native pine in Iowa. This
fast-growing tree is easy to transplant and is well adapted throughout
most of eastern and central Iowa. Its needles are thin and soft, and they
make a beautiful sound on windy days (most days in Iowa). White pine will
eventually reach a height of 50 to 80 feet, with a very attractively shaped
mature crown. They are nearly free of major insect and disease problems
in Iowa.
Despite its name, Kentucky coffee tree (Gymnocladus dioicus) is
another Iowa native. Unable to buy Colombian Supremo or Kenyan AA, early
pioneers in Iowa tried to make coffee from the bitter-tasting beans of
this legume. The result was a beverage that only the thirstiest pioneers
could choke down. But Kentucky coffee tree is a wonderful and very under-used
tree for our landscapes.
Kentucky coffee tree is beautiful year-round. In summer, its light, dappled
shade resembles that of honey locust (another legume). In late fall through
mid-spring, its distinctive silvery, scaly bark and stout, crooked branches
make an attractive pattern.
Female Kentucky coffee trees produce hefty chocolate-brown pods, which
add to the tree’s visual interest in the winter. A moderately slow-growing
tree, it eventually reaches a height of 60 to 75 feet. I’ve never
seen a significant disease or insect problem on the Kentucky coffee tree.
You can find it in Iowa nurseries and garden centers, but you may have
to search a bit.
Norway spruce (Picea abies) is not an Iowa native or even a U.S.
native, but it thrives in Iowa. Once widely planted here as a landscape
tree, it has been elbowed aside in recent years by glitzier relatives
like blue spruce. Norway spruce has its own appeal, though.
For one thing, it isn’t bothered by the serious fungal diseases
– Cytospora canker and Rhizosphaera needlecast – that stalk
blue spruce. Norway spruce grows faster and, with its characteristic drooping
branches, produces a more graceful shape than the stubbier, chunkier blue
spruce. Just make sure you give a Norway spruce plenty of room, since
it can easily cover a 30-foot-diameter circle at ground level once it
matures.
What about small trees?
My personal favorites are crabapples. That’s right, crabapples,
that widely planted but much-dumped-upon group. Crabs are tough, adaptable,
beautiful trees that are trouble-free if you plant the right cultivars.
Look for cultivars in the nursery or garden center with a high (not low,
not moderate) level of resistance to the fungal disease apple scab, and
you’ll never experience the annual leaf loss and bare-branches syndrome
that degrades the appeal of scab-susceptible crabs. In modern crab cultivars,
you can find any tree shape, flower color, and fruit characteristics you
want with high resistance to scab.
Another small-tree favorite of mine is Japanese tree lilac (Syringa
reticulata). Unlike the more familiar shrub lilacs, this lilac reaches
20 to 30 feet in height. Its many virtues include showy, fragrant sprays
of flowers in early to mid-June, attractive cherry-like bark, and a graceful
silhouette in winter. It is hardy throughout Iowa and has few disease
or insect problems. Like Kentucky coffee tree, it is under-planted but
is rapidly gaining popularity.
Experience with good and bad trees over 17 years has convinced me that
white pine, Kentucky coffee tree, Norway spruce, crabapple, and Japanese
tree lilac are great trees for Iowa. There’s one risk, though: if
you plant these trees, plant pathologists in Iowa will soon have nothing
to do.
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ml: isugarden
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