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.
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.
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."
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.