Southwest scourge

Tips in the battle against the pesky, persistent Siberian elm

by Anne Poirot

They grow from foundations, cracks in the pavement, barren lots and other dry, inhospitable places. Every spring, their button-sized, paper-thin seed pods take flight, floating from yard to yard, filling the air and covering the ground in white. They sprout almost overnight, and you cut one down, only to have its stump sprout several more branches like a vegetative hydra. Of course, we are talking about the ubiquitous and invasive Siberian elm, aka Ulmus pumila. And more than likely, you have one growing in your yard.

The Siberian elm is not native to Colorado. According to Ben Bain, La Plata County Weed Control Manager, the tree came from northeast Asia to the U.S. as early as the 1860s, used as a fast-growing windbreak across the Midwest. It was likely brought to the Southwest in the 1920s. The Siberian elm is now listed as a noxious weed in Colorado and is a bane to many residents. So, what can you do?

Well, first the “goods.” As mentioned, the Siberian elm grows quickly, is droughtresistant, provides shade and can grow in poor soil conditions. However, the trees are not good at sharing water with native species and other plants. The tree was defined by notable horticulturalist Michael Dirr as “one of, if not the, world’s worst trees … a poor ornamental that does not deserve to be planted anywhere.”

Another problem: Siberian elms produce billions of seeds every spring. If you’ve seen the piles of seeds in street corners, gutters or your garden, you al- ready know that the germination rate is extremely high.

Once a Siberian elm takes hold, it quickly out-competes desirable native plants, especially in sparsely vegetated or disturbed areas, according to a U.S. Forest Service report. A high density of Siberian elm can reduce shade-intolerant species and decrease overall diversity.

According to Bain, Siberian elm also have deep roots, which enables them to grow fast but also produces a weak tree with branches prone to breaking and falling, especially during heavy snow. Their root system also impacts pipes, sidewalks and other infrastructure. And with wood that burns very smokey, the Siberian elm is not even ideal for a campfire.

Trying to contain the seeds and trees spread may seem overwhelming, or even hopeless. But knowledge is power. The aforementioned Forest Service report recommends hand removal of new sprouts, cutting back of additional growth at the base of larger trees, treating stumps and root systems with chemicals and “girdling” (cutting a deep ring around the trunk) of trees bigger than 3” in diameter.

The guide also includes tips to keep your Siberian elm population in check:

• Maintain healthy and diverse plant communities to prevent infestations.

• Limit disturbance and/or promptly revegetate disturbed areas with desirable perennials, especially perennial grasses.

• Detect and eradicate new populations of Siberian elm as early as possible.

• Combine mechanical and chemical methods for most effective control.

• Graze goats (if you can) along corridors of heavy new growth of seedlings.

Bain also recommends a treatment such as Rodeo Aquatic Herbicide (water-safe, but wear protective equipment), which has been tested by Mountain Studies Institute as an effective way to treat elm stumps.

Homeowners can receive assistance with a free weed control plan from the county and a 50% rebate on material costs. Bain said although other invasive species are higher on the list than the Siberian elm, it is important to pay attention to invasive trees as they are more difficult to remove once established than smaller plants.

But most importantly, don’t wait. Siberian elm can dominate new locations in a few years due to its adaptability, high rate of germination and rapid growth. Awareness is the first step, followed by action.■