These ornamental trees also are valuable for their timber which,
being tough, is used for tool handles and sports equipment.
Unfortunately, a new invasive and exotic pest—the emerald ash
borer— threatens these in the Midwest and mid-Atlantic states, and
is slowly spreading throughout New England. It now has been found
in Vermont, too, and some experts predict that within 10 years
there will be few ash trees left there. The purple rectangles you
may see hanging along roads from trees are monitoring traps for
this pest. Since trees affected with this borer lose half their
leaves in 2 years and often die within 4 years, it may be wise to
plant trees other than ash. Or, if you have ash trees, you may
want to plant others growing near them as future replacements.
This introduced pest was first spotted in southeastern Michigan
near Detroit in 2002, likely coming into our country from Asia on
wooden packing materials. A study was begun in 2003 by Dr. Bert
Cregg and others at Michigan State University, near the epicenter
of the original outbreak, on suitable alternative trees to the
ash. Recently, several cities and towns in Vermont have begun
planting replacement trees near ash, so they’ll be established
when the ash trees die.
If you’re planting more than one tree, it’s best to plant a
diversity of species. This is better for wildlife and, if another
pest or disease comes along, it will most likely not affect all
the trees. A research geneticist with the U.S.D.A. in 1990 (Dr.
Frank Santamour) is credited with popularizing the 10-20-30 rule
for planting, to avoid catastrophic losses from tree pests. This
rule says to plant no more than 30 percent of the same family
(such as the maple family—now reclassified by botanists as part of
the soapberry family), no more than 20 percent of a genus (such as
maples), and no more than 10 percent of a species (such as sugar
So, to start with maples, there are several that you might
consider instead of ashes, including the sugar (Acer saccharum),
red (A. rubrum), Freeman (A. x freemanii)—a hybrid
of red and silver maples, and Miyabe (A. miyabei). All
these are hardy to at least USDA zone 4 (average winter minimum
temperatures of -20 to -30, F). The Miyabe can reach 25 feet in
10 years. 'Morton' (also seen as State Street) is a Miyabe
cultivar (cultivated variety) from the Morton Arboretum near
Chicago, having a dense crown and dark green leaves.
Even though Norway maples (A. platanoides) have been
widely planted in the past, they are no longer recommended as they
can be quite seed invasive. Make sure to not confuse the ‘Crimson
King’ Norway maple with its dark red leaves, with the red maple
There are several Freeman maple cultivars available, including
the broadly oval Autumn Blaze, the upright Scarlet Sentinel, and
the narrowly upright ‘Armstrong’. Freeman maples are generally
orange to red in the fall, 40 to 60 feet tall, and can tolerate
drought or wet soils when established. Celebration is a
particularly drought-tolerant cultivar, with yellow fall foliage.
There are many red maples to choose from, fall colors varying
with cultivar, but generally with a red effect in spring from the
seeds and emerging leaves. Most are dense and
oval in shape, 40 to 60 feet tall. Some tolerate wet soils, and many are moderate to fast growing. A few examples include Autumn Flame which, as its name indicates, has bright red fall color; Brandywine has a deep red fall color; Red Sunset is bright red to orange in fall; Karpick is orange to yellow in fall, with a narrower habit; and October Glory turns orange to red early in fall.
Sugar maples grow 40 to 80 feet tall, generally with a rounded
shape. Although they grow relatively slow, they generally are
long-lived. Most know the yellow to orange gorgeous fall colors,
and the leaf shape from the symbol of Canada. Of course, it is
the Vermont state tree. Examples of this species include ‘Green
Mountain’, which is orange to scarlet in fall, broadly pyramidal,
and somewhat faster growing; similar is the newer Fall Fiesta;
‘Goldspire’ is narrower in shape, turning orange-yellow in fall.
All three linden or basswood cultivars (Tilia) in the
Michigan trials have proved outstanding. After 10 years of
growth, 'Redmond' (T. americana) was 20 feet tall,
'Greenspire' (T. cordata) was 22 feet, and American Sentry
(T. americana) was 23 feet. All are pyramidal with dark
green leaves. 'Greenspire' is hardy to zone 4, the other two even
colder to zone 3.
Several oaks (Quercus) have proven good ash alternatives,
although they may grow more slowly. The northern pin oak (Q.
ellipsoidalis) may reach just over 10 feet high in 10 years,
is hardy to at least zone 4, is native to the Midwest, and doesn't
get the yellowed chlorotic leaves you may find on the standard pin
oak (Q. palustris). A couple other of the hardier oaks
to consider are the Bur (Q. macrocarpa) and the Swamp white
(Q. bicolor). Other good oaks, hardy to the warmer zone 5
found in much of central New England, include the shingle (Q.
imbricaria), chinquapin (Q. muehlenbergii), and the
sawtooth (Q. acutissima).
It's ironic that some of the American elm replacements, bred to
resist the Dutch elm disease, now are recommended to replace ashes
as these are killed by the emerald ash borer. Accolade elms are
hardy to zone 4, and fast growing-- reaching 27 feet after 10
years. Triumph elm, also developed at the Morton Arboretum as was
Accolade, has a similar growth rate but is rated hardy to the
warmer zone 5 (average annual minimum of -10 to -20 degrees, F).
The maidenhair tree (Ginkgo biloba) has a similar yellow
fall color to ash, with a pyramidal shape when young and
wide-spreading when older. It is a tree that has been around for
150 million years, and has a unique triangular leaf shape. It
tolerates most soils and tough conditions. A native tree tolerant
of tough soils and conditions, the Kentucky coffeetree (Gymnocladus
dioica) has fruit (beans) that were used by native Americans
to brew coffee. It can be a slow grower, produces an irregular
open habit, and has yellow fall color. Amur corktree (Phellodendron
amurense) is hardy to zone 3, rounded at 40 feet eventually,
with yellow to bronze-yellow fall color, a moderate to fast growth
rate, and tolerates drought and pollution.
Hackberry (Celtis occidentalis) is native to much of
eastern North America and tolerates dry, compacted and alkaline
soils. When mature, it reaches 50 or more feet tall, with a vase
shape and arching branches. Fall leaves are yellowish. The native
yellow buckeye (Aesculus flava)— is hardy to zone 4 and can
reach about 20 feet in 10 years, forming a rounded habit. For a
lower tree, consider the American hophornbeam (Ostrya
virginiana) with its flowers resembling hops. It is hardy
to zone 4, but rather slow growing, reaching 14 feet in 10 years.
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