From The Ventura County Star
October 14, 2005
Space invaders
Non-native plants can grow rampant in mild climate
By Lisa McKinnon
For Southern California gardeners, October can be one of the busiest months of the year. It follows on the heels of the moisture-sapping heat of summer, offering a window of opportunity for getting new plants into the ground so they can develop healthy roots before winter rains come.
But just because certain shrubs, grasses, ground covers and trees are available from nurseries and garden centers for fall planting doesn't mean they belong in your yard -- ever.
That's the message of the California Invasive Plant Council in Berkeley, which is so troubled by the notion of non-native plants gone wild that it presented a symposium on the subject last weekend in Chico. Among the topics discussed by botanists and agricultural commissioners in attendance was "Are We Creating the Ideal Conditions for Arundo donax Invasion in California?"
For everyday gardeners, the Latin has been translated into plain English: Educational brochures published by the council advise taking a firm, not-in-my-backyard stand against these strangers to the California landscape -- strangers like the Mediterranean native Arundo donax, commonly known as giant reed.
All kinds of plants -- eucalyptus trees from Australia, fountain grasses from Asia and Africa, periwinkle from southern Europe -- grow well in California's myriad microclimates, and that's the problem: After moving in and taking root, some take off, pushing out native plant species and damaging wildlife habitats in the process.
These botanical space invaders may block streams, leading to flooding. Their abundant vegetation can become a fire hazard. Just keeping up with, let alone eradicating, their vigorous growth can cost farmers and other keepers of the land hundreds of thousands of dollars, said David Magney, an Ojai-based botanist, biologist and geographer.
"The appearance of each new invasive species raises the question: 'How do you control this one?' It adds up quickly."
A growing problem
Giant reed is particularly vexing, added Magney, whose company, David Magney Environmental Consulting, has been called in to restore, monitor and map out wetlands and other habitats in Ventura, Santa Barbara, Los Angeles and Contra Costa counties.
Thought to have been introduced to California by missionaries who turned its hollowed-out stalks into musical instruments, giant reed later was valued as a visually striking addition to the landscape, and as a fast-growing windbreak.
Too fast, it turns out. The perennial grass today lives up to its "giant" name, reaching heights of 30 feet in river beds and other waterways, its thick rhizomes, or stemlike roots, digging into concrete and damaging bridges. Encouraged by the heavy rains of last January, the giant-reed crop is especially virile this year, Magney added.
Also wreaking havoc is tree tobacco (Nicotiana glauca) from South America, its leaves poisonous when eaten; Scotch broom, prized by gardeners for its cheery yellow flowers but disparaged by proponents of California-native plants for its habit of running roughshod over wildlands, and pampas grass, an ornamental plant from Argentina. It marches up and down California like a bunch of feather-headdressed Vegas showgirls, trampling sensitive coastal habitats with their high heels.
Consider, too, the Cape ivy, native to South Africa.
Once a popular ornamental plant because of its star-shaped leaves, it somehow managed to escape the confines of domesticity and now can be found draping itself over bushes and dangling from trees in the hills around Lake Casitas, said James Downer, a farm adviser for the University of California Cooperative Extension in Ventura County.
"It's just growing wild up there, with no one stopping it. It's like kudzu," Downer added, referring to the Japanese vine that, left unchecked, has been known to cover entire buildings in the Southeast.
Chaotic exotics
Not all non-native plants are bad characters, notes the California Invasive Plant Council, or Cal-IPC.
The nonprofit organization made up of public and private land managers, ecological consultants, researchers and citizens limits its do-not-plant list to "invasive exotics." These species spread via seeds that germinate wherever they are deposited by birds or the wind, or by roots that replicate themselves like something out of a horror movie, without help from human hands.
The Cal-IPC advises that landscapers and home gardeners not purchase such plants, and that they rip out any volunteers found growing in the yard -- especially if that yard borders on a natural area or wildland preserve.
The council also offers a list of landscape-friendly alternatives to help fill in any resulting gaps. Most are California natives; many were selected to mimic the appearance, if not the pesky growth patterns, of the problem plants they are meant to replace.
Substitutes for the spiky asparagus vine (Asparagus asparagoides) and the trailing periwinkle (Vinca major) include the spiky-leafed common yarrow (Achillea millefolium) and the compact Beach strawberry (Fragaria californica). Replacements for giant reed and pampas grass include lavender (Lavendula species) and California fescue (Festuca californica), a drought-resistant native with blue-green leaves.
But one gardener's desirable plant may be another's weed, good only for being ripped out and stomped into submission.
Witness the iceplant, touted by placards in the city of Santa Barbara's firescape demonstration garden as a good thing to have around the house because its low growth pattern and high moisture content might help stall an approaching wildfire.
Conversely, the Cal-IPC includes iceplant (Carpobrotus edulis) on its do-not-plant list because it forms an impenetrable mat that competes for space with several rare and threatened plants. Plus, small animals can easily carry its seeds from landscape settings into natural areas.
The same goes for cotoneaster (Rosaceae), which also is featured in the firescaping garden in the Santa Barbara hills. Cal-IPC puts its franchetii, lacteus and pannosa varieties on the "moderate" danger list because the plants have "substantial and apparent, but generally not severe, ecological impacts on ecosystems ..."
At a store near you
Cal-IPC literature explains such differences of opinion in regional terms: A plant that behaves itself in one climate zone may wreak havoc in another. So it is that some plants identified as invasive exotics, like periwinkle, may be readily available at the local garden center.
Such plants also may be available because there is consumer demand for them, possible problems be darned.
And that is because some gardeners are "not living within their environment. They want to recreate what they've seen growing in Europe, or on the East Coast," said Magney, who is involved with the Channel Island chapter of the California Native Plant Society.
"We need to be attuned to what grows here naturally and adapt ourselves (to those plants) instead of the other way around."
Available on the Cal-IPC Web site is a business card-sized greeting, suitable for downloading, printing and handing out to the nearest nursery manager found carrying fountain grasses and other presumed botanical no-nos.
"While shopping today, I noticed that you stock the following plant(s), which, to my knowledge, is known to be invasive in California's natural areas," it reads, the type followed by several blank lines just waiting to be filled in. "Please consider stopping the sale of this plant(s).
lmckinnon@VenturaCountyStar.com