Interior West 6

BY LAUREN SPRINGER / Fort Collings, Colorado, USDA Zone 5


Weeds of the West

Tom Whitson, editor

The Western Society of Weed Science and the Western United States Land Grant Universities Cooperative Extension Services; 1992

To conquer one’s enemies, one must know them. This book’s excellent photographs identify the interlopers, and its information on their habits and life cycles prepares the gardener to deal with them. You may actually be won over by weeds, for they are charming and fascinating in their own right.

The Three Banditos

One would think that in the difficult climate of the Interior West, weeds might struggle. Not so. There are many unwelcome plants thriving in these parts, but three particular creeping herbaceous perennials have made themselves so utterly comfortable here, and are so adaptable and antisocial, that they deserve special attention: Canada thistle, leafy spurge, and field bindweed—the three banditos.

They came from Eurasia in agricultural crop seed well over a century ago, and share lengthy seed viabilities of eight to 50 years and tunneling roots that can send up a shoot on pieces less than an inch long. These roots may reach down six to 15 feet. The plants adapt to all soil types, tolerate intense drought, and ignore high altitude and cold. They prefer to colonize disturbed areas but easily move into pristine climax communities of native plants, once given a toehold. In other words, these are truly uber-weeds. Of the three, only Canada thistle benefits significant numbers of insects and birds. Leafy spurge is toxic to cattle, causing mouth and digestive irritation severe enough to kill. All three form dense monocultures by nature of their aggressive growth habits and possibly also with the help of allelopathic chemicals (secreted by their roots), which suppress neighboring plants.

Canada thistle (Cirsium arvense) forms colonies of prickly-leaved, one- to four-foot-tall stems topped with a cluster of rosy purple, fluffy flowers in midsummer. Roots can spread 15 feet; a piece of root can survive for 100 days without light and still grow on. The foliage emerges in leafy rosettes in midspring. Birds and wind help spread the seed.

Leafy spurge (Euphorbia esula) is a pretty thing. I was smitten by its chartreuse-yellow flower umbels my first May in Colorado, before I knew of its self-important ways. It has the characteristic milky sap of its genus, and grows one to three feet tall on slender, unbranched stems clothed in blue-green, narrow foliage. The seeds are ejected up to 15 feet from the plant and also float, spreading the plant along ditches and streams. Close to three million acres in southern Canada and north-central United States have been overtaken by this noxious plant.

Field bindweed (Convolvulus arvensis) is a twining plant with showy white or pink morning-glory-like flowers that carry on from June until frost. When not given other plants or objects to clamber over, it sprawls prostrate across the ground in dense mats of arrow-shaped blue-green foliage. If it weren’t so obnoxious, it would make a fabulous groundcover.

The key to controlling the three banditos is starving them to death. By consistently pulling new growth, or smothering it with an impenetrable plastic barrier, or damaging the foliage repeatedly with a blow torch, herbicide, or vinegar spray, the plant cannot replenish its underground reserves. Over time it will succumb; a young patch can be killed off in one growing season, but an established stand may take several years of vigilant activity. Be on the lookout for new seedlings; the three banditos are now as much a part of the West as ponderosa pine, penstemon, and prickly pear. H


Yellowhorn Xanthoceras sorbifolium

This 15- to 24-foot small tree from northern China is one of the few hardy members of the otherwise tropical Sapindaceae. Its pinnate deciduous foliage and large trusses of fragrant white spring flowers have an exotic flair. Each blossom’s central blotch changes from yellow to red upon pollination. Sun-loving yellowhorn is slow growing but adaptable to most soil types. Hardy in USDA Zones 4–7. Sources, page 96.

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