Environment & Science

Bad Seeds, Part 2 - Invasive plants in your local nursery

One of the few Humboldt lilies (also called leopard lilies)  that survives in Big Santa Anita canyon. English Ivy has smothered most of  the native plants along a 3-mile stretch of the stream.
One of the few Humboldt lilies (also called leopard lilies) that survives in Big Santa Anita canyon. English Ivy has smothered most of the native plants along a 3-mile stretch of the stream.
Ilsa Setziol/KPCC

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About two dozen non-native plants have escaped Southern California gardens and are threatening a number of the state's plants and animals. Not only are these invasive plants very difficult to control, they are on sale in local nurseries.

The problem is visible high in the San Gabriel Mountains, above Sierra Madre, where Sturtevant Falls spills into Big Santa Anita Canyon. For more than a century, people have come to this secluded spot to escape the city.

Alders and sycamores still shade the stream. A very few orange leopard lilies persist. They glow like paper lanterns amidst a vast green shroud of a common garden plant – English Ivy.

Cabin owners who lease land in the canyon planted the ivy decades ago. They tried to control it, but their efforts failed. Today it has choked out most of the native plants.

English Ivy is only one of about two dozen invasive garden plants threatening California’s native plants and animals. Conservationists are frustrated not only that these invasives are available in some local nurseries, but that the state has done little to remove them from the market.

"Our state agricultural agency regulates weeds that are primarily agricultural pests," says Drew Ready of the Watershed Council.

"These wildland weeds are now on the radar. There's movement to ban some of them from the trade, but we’re still probably a few years away from that."

Oregon recently banned English Ivy, but California law precludes banning plants sold in nurseries. And the state’s conservationists are so wary of alienating California’s large horticultural industry that most are not pushing to change the law.

Some are advocating a more incremental approach.

"In this day and age of strapped budgets, the idea of passing simple legislation that says you can’t sell this plant and then trying to enforce it is going to be less productive than actually getting the industry on board and developing the mentality that plants they sell have to be safe," says Doug Johnson, head of the California Invasive Plant Council.

The nursery industry says it has developed that mentality. "I feel confident the nursery industry wants to be part of the solution," says Nicholas Staddon, director of new plants for Monrovia Growers. "The opportunity ... is to breed traits into plants that make the plant a better-behaved garden plant."

The industry has developed sterile versions of some runaway plants, but there is a lack of standards. And scientific research is sparse. Plus, plants can cross-pollinate in the wild, creating hybrids.

Further complicating matters, an invasive might be harmful in some habitats, and harmless in others. For example, in Southern California, ivy only invades stream banks, so some in the industry have argued that it should not be restricted statewide, or even regionally.

Nicholas Staddon of Monrovia Growers says some invasive plants are very useful in gardens. "Where is the happy medium between ... iceplant [or] ivy that can be planted in ... highly populated areas where they will never have the opportunity to become invasive?" he asks.

The Watershed Council's Drew Ready doubts that approach will work. "With the ivies, the berries will travel as far as a bird will," he says. "A very urban planting of ivy could get established miles away from the source."

Ready estimates about 5 million California homes are within a few miles of a wildland, creek or park.

Meanwhile, invasive plants remain on sale at nurseries. A group of growers and conservationists has taken one step to address the problem: it has produced a website and brochures that profile the rogue plants and recommends alternatives that don’t damage wildlands.