In the Garden:
Western Mountains and High Plains
February, 2005
Regional Report

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Purple loosestrife is an import from Europe that's invading wild areas all across the U.S.

Noxious Weeds

I was a child growing up on a small ranch in Western Colorado when I first learned about noxious weeds. Knapweed (Centaurea diffusa) is a relative of the common garden plant, bachelor's buttons, but it's an escapee in our region, and it invaded our alfalfa fields. The plants grew in patches, producing thousands of seeds to be dispersed by the wind. Pulling it wasn't an effective control, so the infested areas had to sprayed with an herbicide that rendered the soil sterile for a year or more.

Now, as a horticulturist, I'm faced with how to handle the invasive characteristics of introduced plants. These are plants that did not originate here, and they often lack natural enemies -- except browsing goats. Once happily established in the landscape, they soon become so aggressive that they crowd out other desirable plants or can even destroy a natural ecosystem.

Certain weedy types spread either by seed or by root structures such as stolons and rhizomes. They are able to take over certain areas and continue to move on. Humans and animals contribute to the problem by inadvertently spreading the seeds. Weed experts are supplying evidence that the impact invasive plants have on native ecosystems is of great concern. These noxious weeds are now considered a threat to the environment, and they also affect the economic value of our lands.

To many people, the solution is to plant only natives, since they are indigenous to a region. New plants can pose an ecological threat to farmland, national forests, natural drainage areas, and areas of our wilderness. While I can become excited about some of the new plant introductions that adapt well in the region, I'm inclined to follow the wisdom of nature and be protective of our ecosystem and native plants that live there.

There is a growing list of noxious weeds or invasive plants, but there's only space here to feature a few of great concern. Check with your local weed district or land grant university to find out more about the specific problem plants in your area.

Purple Loosestrife
Perhaps the most recognized and invasive ornamental native to Europe is purple loosestrife (Lythrum salicaria). It's a rugged survivor, with upright stalks 2 to 5 feet tall. The flowers are attractive, purplish rose spikes. The mature plants can produce millions of seeds, and the plant can even grow from broken segments. It prefers moist environments and has become a big problem in riparian ecosystems. In poses a threat to wildlife habitat, restricts the flow of irrigation water, and clogs natural drainage basins.

Control of loosestrife is difficult since it grows in waterways, making herbicide applications more threatening to wildlife. Plants can be dug or pulled out by hand, but good luck. If you see purple loosestrife, report it to your weed district.

Russian-Olive
Another intruder to riparian areas and along rivers, streams, and ditches is Russian-olive (Elaeagnus angustifolia). Once a widely used tree for windbreaks, it has engaged us in a subtle takeover. Seedlings should be dug as soon as they sprout, and mature trees removed.

Mediterranean Sage
Mediterranean sage (Salvia aethopsis) is a native of the Mediterranean and North Africa. A member of the mint family, it's a biennial that grows 2 to 3 feet tall. The first season it grows a rosette with large, grayish, aromatic, woolly leaves. In the second year it sends up flowering stalks with showy white blooms that eventually produce thousands of seeds. Cutting it out in the first season is a good cultural management control method, or you can spot-treat with an appropriate herbicide.

These are but a few of the invasive or noxious plants that we need to be on the lookout for. Once thought of as ornamental garden plants, they have the potential to invade, rather than complement, the landscape.


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