Southwest Gardener

Rethink Aspens for Your Yard

Quaking aspen (populus tremuloides) prefer the cooler climates offered above 7,500 feet.
Marisa Thompson, December 2017
Posted

Q: I have a spot with southern exposure in my yard where I would like to plant a quaking aspen (5,792 feet elevation). Is quaking aspen suitable for this environment?

A: I traveled across New Mexico during the past few weeks, enjoying the striking fall colors. It’s no surprise that you’re feeling inspired to plant such a sensational tree.

Quaking aspen (populus tremuloides) prefer the cooler climates offered above 7,500 feet. Some say they can be planted above 6,000 feet, but only with very special care and in a very cool spot along the north or east side of a building, where the soil remains mostly shaded.

Even if you babied your tree by providing extra water, it would likely suffer from heat stress every summer.

Another reason to resist the urge for urban plantings of aspen trees is described by Tom Zegler, a New Mexico state forester for the Socorro District. He warns that “their biological strategy is at odds with what we want from a tree. As an aggressive pioneer species with a short lifespan, they budget energy for height growth and root suckering at the expense of defense and maintenance of individual stems. In fact, above-ground biomass is a dispensable part of the organism. This is why aspen in a horticultural setting are dependable for nothing but eventual disappointment.”

When selecting plants for our gardens, the top concern is usually cold-hardiness, which refers to the minimum temperature a plant can be exposed to and still survive. The USDA developed cold-hardiness zone maps of the U.S. to help gardeners match the hardiness of a particular plant with the zone in which they live. In New Mexico, cold-hardiness zones range from 4b, where average annual extreme minimum temperatures are -20 to -25 degrees, to 8a, with minimum temperature from 15 to 10 degrees.

Heat tolerance also needs to be considered. The American Horticultural Society created a tool akin to the USDA cold-hardiness zone map. This Plant Heat-Zone Map defines zones based on the average number of days per year above 86 degrees. According to NMSU climatologist Dr. Dave Dubois, average temperatures in Albuquerque’ Northeast Heights have continued to increase over the past few years.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center. She can be reached at desertblooms@nmsu.edu.

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