Ask SAM: Where do weeds come from?

This column is provided by Larimer County Extension's Small Acreage Management (SAM) Program to assist rural residents.

Dear SAM,

Where do all these noxious weeds come from?

Sandy

Dear Sandy,

There seem to be as many paths for a weed seed to travel as there are weeds.

Many of our worst weeds came to North America in the 19th century. Often, the weed seeds were hiding in bags of grain or crop seed imported from Europe or Asia.

Some weeds have entered as seeds in ships, cars, planes and trains. During the 1800s, ships traveling across the ocean often used soil or water as ballast. Upon arriving in North America, ballast was dumped and the seeds were thus delivered.

Today, weeds get caught on the bodies of cars, trucks and ATVs. As the vehicles travel down the road, the weeds and their seeds are transported to an area where a new infestation takes root.

Weeds can hitchhike as contaminants in hay. This has been a concern during our recent drought, as livestock owners have looked outside our region for sources of hay. Yellow starthistle is a weed of particular concern as a contaminant in hay coming from far western states.

Sometimes a common name describes the travels of a weed. Though its origins are in Europe, Canada thistle got its name because people believe it made its way to the United States from Canada. Australians use the name "Californian thistle" to describe the same plant, because they believe it entered their country in a shipment from California.

Some of our most devastating weeds, such as tamarisk, were introduced to North America intentionally as tools for erosion control. Now an aggressive riparian weed, tamarisk is attacking several Front Range river corridors. Ironically, nurseries in the northeastern United States continue to sell tamarisk as an ornamental.

Currently, many of our most problematic new weeds are originating as escaped ornamentals. Examples include yellow toadflax, also known as butter-and-eggs, myrtle spurge and Mediterranean sage. Gardeners plant these species because they are drought tolerant, hardy and spreading. They are also prolific seed producers. These same qualities make the plants invasive once they escape the garden.

Keep this in mind if you are planting a drought-tolerant garden. The xeriscaping trend has led to the introduction of many drought tolerant species from throughout the world. While most of these species will never become a problem, some could become our next noxious weed menaces. Avoid using plants in your landscape that have the characteristics noted above. Try to use native plants in your xeriscape as much as possible.

SAM

Have a question about rural living? Write to Ask SAM, Larimer County Cooperative Extension, P.O. Box 543, Fort Collins, CO 80522.