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When the beautiful go bad

Special to The Times

WEED. We need only one syllable to differentiate friend from foe in our gardens. Yet the word seems inadequate for a new generation of weeds -- plants that we find beautiful or delicious when we cultivate them but that have escaped into the wild to potentially catastrophic effect.

No single source tells the story of the shifting definition quite so methodically as “Weeds of California and Other Western States.” When UC Davis weed scientist Joseph M. DiTomaso published the two volumes in 2007, they included more than 700 specimens, just about every plant that has stung, inconvenienced or merely displeased people this side of the Rockies. There in the 1,800-plus-page rogues’ gallery, many of our classiest nursery salads and ornamentals have rap sheets. Nasturtiums, weeds? Ice plant? A weed?

The longer one spends with the new directory, the clearer the modern message about weeds becomes. The emphasis is no longer on what wild plants are doing to our gardens but what our gardens are doing to the wild.

For lack of a better term, this new class of super weed is called an “invasive.” Grammarians, cringe and get over it. “Invasive” has become a noun. It’s for the lovely and luminous green shrub tamarisk, aka saltcedar, now sucking the Colorado River dry. It’s for Arundo donax, or giant reed, the bamboo-like hedging plant now clogging Southern California waterways and destroying vital wetland wildlife habitat. It’s for the English and Algerian ivy slowly suffocating our pine forests, the blue-gum eucalyptus whose resinous limbs add explosive fuel to fire zones, and the ice plant choking sand dunes where native plovers can no longer nest.

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If it sounds grim, it is, but nobody’s blaming us. The nursery trade unleashed many of these plants before it or we knew better. Pampas grass now lining much of the Pacific Coast Highway is a perfect example, DiTomaso says. Introduced by a Santa Barbara nursery in 1848, it seemed containable. When commercial production began in 1874, the plants were propagated by dividing them at the root, and only females were selected for their superior plumes.

“To simplify the process, they turned to seeds and planted the seeds and sold plants as tufts before they flowered, so they did not know if they were males or females,” DiTomaso says. “Males got out in the environment and boom, within about 15 years, the plant became an invasive problem. We actually had the solution, but we didn’t stick with it.”

According to Drew Ready, program manager for the Los Angeles and San Gabriel Rivers Watershed Council, pampas grass is now one of the worst offenders, destroying vital bird and marine habitat in Southern California’s most sensitive wetlands.

Yikes. We just liked the wavy plumes.

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The surprising thing is that the runaway fancies causing problems in the garden -- say, the passion vine that becomes 300 vines -- are not necessarily the most wanted of invasives, at least here in California. (Passion vine is a nightmare in Hawaii.) Some of the most common garden weeds of the Los Angeles area, many of them lawn grasses, couldn’t cope in the wild. Rather, we enable them by frequent tillage and chronic overwatering.

But where water-hungry and shade-loving garden plants do escape into the wild, the consequences are devastating, according to Christy Brigham, a restoration ecologist working in the Santa Monica Mountains for the National Park Service.

“It’s so dry here, those creek habitats are hugely important,” she says. “So, for instance, hummingbird sage is a beautiful native that would grow in cool wet areas, especially in Solstice Canyon. Instead, those areas are full of periwinkle and nasturtiums.

“In Solstice Canyon, we’re trying to reintroduce steelhead trout. They need a native plant community to generate the insects to feed the trout. Instead, right now they have periwinkle and nasturtiums.”

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Brigham’s eyes do not light up at the sight of fountain grass fluttering in the breeze along our roads.

“It offers wildlife none of the forage of the native sunflowers that it displaces,” she says. “What’s more, it’s not particularly good at stabilizing slopes.”

If you have a stand that you wish would invade your garden but that has refused, do not doubt the invasive nature of the species. There are two types of fountain grass, or Pennisetum setaceum, commonly found around Los Angeles. One, ‘Rubrum,’ is sterile. The other is anything but, and to judge by the number of runaways choking Southern California coasts and grasslands, even nurseries are not rigorous about which is which.

Rather than stand back and let the state’s exquisite native plants give way to a hodgepodge of escaped ornamentals with little or no wildlife value, the Bay Area nonprofit Sustainable Conservation began pulling together concerned parties four years ago to look at the options.

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Representatives from the UC Davis Arboretum, Nature Conservancy, California Farm Bureau, California Native Plant Society, Huntington Botanical Gardens, California Department of Food and Agriculture and California Assn. of Nurseries and Garden Centers gathered around a table, and soon an umbrella group was formed called PlantRight.

As a first step, PlantRight enlisted master gardeners to scour nurseries to see which invasives were being sold, then began asking the stores and growers to work with them to get the offenders off the shelves in sensitive regions.

THE benefit of this, DiTomaso says, is that regional solutions are crucial. Although ice plants are destructive in a coastal dune setting, they’re a water-wise and fire-resistant ground cover for inland gardens. So a surgical approach to targeting the offenders was needed.

Nicholas Staddon, director of new plant introductions for Monrovia Growers, agrees. Monrovia was one of the first backers of PlantRight, and although his company still grows and sells invasives, he says, it’s working hard and in earnest to keep them off store shelves in sensitive areas. Give nurseries terms they can work with and they’ll buy in, adds Terri Kempton, PlantRight manager for Sustainable Conservation.

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Now the group is focusing on big-box stores. Lowe’s confirms that it is beginning the exhaustive and complicated process of inventorying its stock, pulling offending plants and retraining its growers.

Skeptics need only point out the nasturtium seeds for sale in just about every garden center in Southern California, and PlantRight can seem toothless and wishful. Still, a start is a start, and as a start, PlantRight is exceptionally well organized. A newly revamped website, www.plantright.org, allows gardeners to click on their region and look for local solutions.

The beauty of having botanists and skilled gardeners behind the effort is that consumers are not in for a scolding. For every “don’t,” there are two or more “do’s.” Giant reed is discouraged, but clumping bamboo and New Zealand flax are recommended. Fountain grass is discouraged, but blue oat grass, deer grass and sedges are offered as alternatives.

What Kempton likes about the program is that it gives gardeners a chance to do the right thing while doing the fun thing: buying interesting new plants.

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Once the nursery trade wakes up to the commercial potential of selling those new plants, more stores might begin weeding their shelves in earnest.

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home@latimes.com

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Further reading

Weed guide: “Weeds of California and Other Western States,” by Joseph M. DiTomaso and Evelyn A. Healy, published by UC Department of Agriculture and Natural Resources; $100. Two volumes list about 700 examples. Available through www.calweeds.com.

Weeding sources: For information on invasive plants in home gardens, check with the University of California Cooperative Extension Weed Research & Information Center, wric.ucdavis.edu.

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PlantRight: Sustainable Conservation’s website with regional planting tips for the coasts, coastal mountains, Sierra, Central Valley and deserts; www.plantright.org.

Local outreach: The Los Angeles and San Gabriel Rivers Watershed Council runs an Invasive Plant Monitoring and Outreach Program, www.weedwatch.org.

-- Emily Green


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