Recommended Street Trees for Fall
By Carl Wilson, Colorado State University Cooperative
Extension Agent, Horticulture, Denver County
If you missed spring planting, now is your next best chance to
establish a tree before winter begins.
In the Denver area, a tree's chances of survival increases if its
planted after the summer heat breaks in September, but before October 15. Based on long
term climatic averages, this timing allows trees six weeks to grow new roots before the
soil freezes. This root growth can make a real difference in how well a fall- planted tree
survives the winter.
Keep two tips in mind when you plant street trees.
Look for one of the newer varieties of so-called "skinny
trees" that are much better suited to streetside life.
Check with local government authorities for area regulations
governing tree spacing, location, or non-allowable tree species.
The following trees have been tested by the Colorado State University
Horticulture Department at their arboretum in Fort Collins. They are all selected for
their suitability for street planting although they also will make fine yard trees.
`Autumn Purple' American ash (Fraxinus americana)
is rapidly becoming a Colorado favorite. This tree requires low to medium watering and its
foliage turns a striking shade of purple in the fall.
'Marshall's Seedless' ash (Fraxinus pennsylvanica) also is suitable for street tree
use. This ash turns yellow in the fall.
Japanese pagodatree (Sophora japonica) may be an alternative for people
seeking a flowering tree, but who are wary of severe fireblight-disease outbreaks seen on
crabapple this year. Pagodatree bears large creamy flowers in mid-summer and bead-like
pods in fall.
Swamp white oak (Quercus bicolor)
is a more handsome tree than its common name might imply. It is native to low oxygen, wet
locations, so it adapts well to our heavy, low oxygen clay soils. Some oaks grow very
slowly, but this species is faster growing.
Three options are available for people lucky enough to live along the
Front Range where soils are less alkaline.
'Armstrong' red maple (Acer rubrum)
is one of the best adapted of the red maples for our soil and climate conditions. In
trials at Colorado State, it grows narrow and columnar, and it displays a vibrant red fall
Red oak (Quercus rubra)
turns red in the fall.
English oak (Quercus robur)
is notable for its glossy, dark green leaves throughout the summer.
Both Red oak and English oak are recommended for better, less alkaline
Additional street tree choices for most any location include common hackberry (Celtis occidentalis), littleleaf linden (Tilia americana) and Norway maple (Acer platanoides).
If your nurseryman doesn't stock the desired type or variety of tree,
ask that it be ordered from the supplier.
Photograph courtesy of Judy Sedbrook.
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