Colorado Noxious Weeds -- Part 2

By Marilyn Loser: 2013 November 20

In the last Alamosa Flowers column I asked if you had any Colorado Noxious Weed (CNW) -listed plants in your garden.  I do in mine. Mostly I see B List (those for which preventing new infestations is a high priority) plants in my garden and around town.

I ended the last column with a mention of Magenta Dame’s Rocket and will begin with the same flower. It epitomizes the problem with many invasive species. It has a heavenly aroma and, as Rosemary Parker of Kalamazoo says, it lasts longer than most wildflowers when suck in a jar of water and it self-seeds freely.  And therein lays the problem.  It thrives and crowds out native wildflowers along Michigan’s rural roadsides.  In Colorado about 1,160 acres are infested and those are in Denver and the Summit County west of Denver. I’ve been to online seed sites that say they won’t ship to Colorado and several gardening friends have been told they are a “no no”! Mine are dying out and I’m not encouraging them to thrive.

Two other flowers I transplanted from friends’ gardens (didn’t realize were on List B) are Common Tansy (Tanacetum vulgare) and Oxeye Daisy (Chrysanthemum leucanthemum).  I like the yellow tansy.  It doesn’t need much water or care, grows to over 5 feet in my garden, and is long blooming.  The row of yellow flowers in front of the County Courthouse is this tansy. The white Oxeye Daisy came into my garden when I transplanted Gloriosa Daisies (rudbeckia hirta).  The seed must have been in the soil.  These daisies bloom earlier than the more elegant Shasta Daisies.

Salt Cedar (Tamarix chinensis, T. parviflora, and T. ramosissima).  It’s feathery fall blooming, pink flowers are delightful.  Apparently, it was brought into the country as an ornamental and to stabilize stream banks. It can be very aggressive and invasive.  Each plant can produce 600,000 seeds per year according to the CNW website.

The ‘C’ list includes species that aren’t banned state wide.  Rather, the goal is to develop management plans that “will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions that choose to require management,” according to the CNW website. 

I have one plant on this list and certainly consider it a weed.  It’s Field Bindweed (Convolvulus arvensis) and is in the same genus as desirable morning glories. The vine leaves are similar to morning glories, but usually smaller.  The flowers are white and light pink.  I’ve seen a lot of them around town.  It’s very hard to remove them. The stems are very delicate and break when you try to pull them.  They are very good at growing amongst clumps of perennials and when I use a weed digger, I end up damaging the plants I want to save.

I was surprised to see one of my favorite flowers on the “Watch List.” These are species that “have been determined to pose a potential threat to the agricultural productivity and environmental values of the lands of the state,” according to the CNW website. The purpose is to gather information “to assist the Commissioner in determining which species should be designated as noxious weeds.” Perennial Baby’s Breath (Gypsophila paniculata) is the flower I have.
So what should I do about my noxious weeds?  Naturally, I try to remove any that I consider weeds. But since none are on the ‘A’ eradicate list, I don’t have to remove them.  It seems to me that a major goal is to remove threats to agriculture and the environment.  Are my plants a threat?

I took a closer look at the CNW website (just Google Colorado Noxious Weeds – the URL is very long) and clicked on various noxious species to view maps that show the number of infested acres and where they are in the state. For example, Perennial Pepperweed has infested more than 118,000 acres in the state and the San Luis Valley is a main areas.

Russian Olives have infested more than 10,000 acres in Colorado and Alamosa is clearly listed.  Sadly, birds transport the seeds and often drop them in riparian areas where they displace native species. At this point, I don’t plan to rip out my Russian Olives.

Common Tansy has infested 473 acres and most counties have reported 0 acres or have not reported. The concern is that tansy is toxic to livestock if they eat large quantities and it replaces native plants. Hence, the desire is to keep it from becoming a problem. What to do?  I haven’t decided.

To let me know what you think and to see previous columns, go to

"More in a garden grows than what the gardener sows." Spanish Proverb