Yard plants: Nurturing natives and ousting aliens

By Gary Raham
Nature Writer and Illustrator

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Like many naturalists, I used to be an animal chauvinist. I paid attention to creatures that hopped, scurried, lumbered or slinked across the landscape, and I treated the green stuff through which they moved as potential food, barriers, poisons or decoration.

I'm now reformed. While still enamored by my animal colleagues, I've come to better appreciate the variety and complexity of plants and their natural habitats. In fact, Colorado State University Extension has even honored me with the title of Native Plant Master for completing a series of summer courses at various regional natural areas. I carry the title with profound humility.

Mastery of any topic in biology is a temporary and illusory state at best. But, like a reformed smoker, I'm now prepared to share my epiphanies about the necessity of nurturing native plants and policing the invasion of destructive, alien species.

Why nurture natives?

Plants grow and evolve to match local climates and soil conditions. Those surrounded by concrete and asphalt most of the time may forget that they live in a semi-arid grassland receiving about 14 inches of rain per year and only enjoying 120 to 210 frost-free days.

Native plants have adapted to best flourish under these conditions. They also have accommodated themselves to the community of plants, animals and pathogens that have evolved with them. Longtime ecosystems are also the most diverse in terms of number of species. Diversity provides more choices during times of climate change and variability that make ecosystems more resilient over the long haul.

Alien species may flourish when they first invade new territory because they lack natural checks and balances. They may displace native plant species and in turn alter habitat for animals dependent on specific food plants for survival.

Purple loosestrife (Lythrum salicaria), an attractive lavender flower on tall spikes, serves as an example of how aliens invade new territory both by accident and uninformed design.

Purple loosestrife seeds invaded New England soils in the 1800s largely as unintended cargo in European soils used as ballast in sailing ships. When ships arrived in New York, Boston or other ports, these soils were dumped in coastal "ballast grounds." Loosestrife thrives along canals and other wetland habitats.

Some loosestrife seeds also found their way to the new world stuck in the wool of European sheep exports. Individuals also imported loosestrife intentionally as a medicinal herb to control bleeding and dysentery. Loosestrife gradually moved westward along shipping corridors and beekeepers planted it intentionally as a food plant for their pollinators.

Surprisingly, loosestrife wasn't recognized as a pest species until the 1930s when it began to take over many wetland habitats. While now common throughout much of the United States and Canada, it is still fairly rare in Colorado, and conservationists want to keep it that way.

Culpable gardeners

Gardeners looking for beauty may cultivate aliens instead of natives, not realizing the dangers if their charges escape the yard and run amok.

Toadflaxes, also called butter-and-eggs, became ornamental plants in the 1830s. They have extensive root systems and efficient seed dispersal that makes them hard to control in the wild. Because they like dry summers, they have been spreading in Colorado and now infest more than 40,000 acres.

I've seen toadflax in recent years in natural areas in Larimer County including Reservoir Ridge along the northeast side of Horsetooth Reservoir. While Linaria dalmatica and Linaria genistifolia, the broad- and narrow-leaved toadflaxes, sport beautiful yellow flowers with distinctive spurs, many native alternatives look just as flashy in the garden. Golden banner (Thermopsis ssp.) waves golden pea-style blossoms during summer months. Yellowish to orange wallflowers, Erysium asperum, also make great substitutes.

Recognizing invaders

The Native Plant Master courses are a great way to learn about native and alien plant species if one can carve out the time for three 12-contact-hour sessions during the summer. I thoroughly enjoyed exploring South Valley Open Space, the Plains Conservation Center and Lair 'O the Bear Open Space Park through Jeffco's version of the CSU Extension program between 2004 and 2007. I shared the trail with teachers, retired professors, gardeners and nature enthusiasts of all kinds.

Find details about applying for this program and others like Colorado Master Gardeners at www.answerlink.info under "horticulture." I applied for the courses after hearing about them through the Master Naturalist Program sponsored by Fort Collins - another great way to learn and share knowledge about the inhabitants of local natural areas.

The CSU Extension answerlink site noted above also provides information about all sorts of gardening issues, from xeriscaping to wildlife management, insect information and control, as well as plant-related issues.

Colorado Weed Management Association (www.cwma.org) publishes "Noxious Weeds of Colorado." The ninth addition became available in 2007. They place plants on an A, B or C list. The A list includes species specially targeted for immediate eradication and lists species like meadow knapweed, Mediterranean sage and Medusahead rye. Yellow toadflax and leafy spurge are two of 39 species in the B list, targeted for aggressive management to control their spread. Conservationists struggle to manage C list species like field bindweed that are comfortably entrenched and widespread.

I enjoy the smell and blue-green color of native sage (Artemesia frigida) in my front yard and the yellow blossoms of rabbit brush (Chrysothamnus nauseosus) in my back yard. We nurture Colorado's state plant, the columbine, and have grown the red and yellow daisy-like Gaillardia (blanketflower).

I haven't cut down my Russian olive tree yet, but it may be almost time to say "nyet" to my thorny alien tree and find a native more inviting to nesting birds.

A little animal chauvinism lingers yet.