CHRIS CLARKE: THE IRASCIBLE GARDENER
Invasive plants threaten natives

Posted on Sat, May. 18, 2002

THERE'S A VERY NICE house not far from mine, with a very nice lawn and a very nice bit of garden at the margins. Not long ago, the residents must have decided to fill a little gap with a flowering plant. They picked one with appealing green leaves and bright yellow flowers. They planted it, and it's blooming there now, not much larger than it was in the nursery. It's a scotch broom, Cytisus scoparius, the invasive shrub that now covers huge swaths of the West Coast from Monterey almost all the way to Alaska.

My neighbors' plant has already started to set seeds. Broom seeds develop in little pods. When ripe, the pods explode, sending seeds far and wide. Each plant can produce hundreds, if not thousands, of seeds, which remain viable for quite a few years, waiting for the right combination of sun and moisture to sprout. Sun my neighborhood's got; it's essentially an open oak grassland with houses. Moisture will come soon enough. Probable result: hundreds more little broom plants, each making thousands of seeds.

Sweep out broom

The problem? Other plants can't compete. If you want to preserve your native plants, or keep your rose bushes weed-free, or in fact grow anything other than broom, you need to pull the broom plants. This is harder than you might think. The plants send a tap root down, seemingly, to hell. There's a special tool, called a weed wrench, designed to pull broom; it doesn't always work. California government and private agencies spend millions of your dollars every year trying to beat back broom, and untold numbers of private landowners spend days or weeks each year pulling it, all because people thought it looked nice.

I don't blame my neighbors for planting the stuff. It does look nice. It's a reliably yellow flowering shrub for people who miss forsythia. And -- this is the kicker -- some nursery sold it to them, perfectly legally. Their broom even had the little nursery tag still on it. I sneaked a look at the tag, and the only hint that this plant might be less than perfectly behaved was "may reseed."

"May reseed." That's like saying a fifth of Old Overcoat "may cause drowsiness."

More invaders

It isn't just broom. Shopping for fruit trees this month, I found not one but two nurseries selling flats of Aptenia cordifolia, a charming little succulent ground cover with an appealing red flower that is now choking the life out of wetlands from Los Angeles to Oregon. It smothers irrigation ditches in the Central Valley, sucking up precious agricultural water and forcing farmers to spend money to get rid of it.

Right next to the Aptenia in one nursery were flats of English ivy, a plant so invasive that even its fans regard it somewhat ruefully, to mix a horticultural metaphor.

You can still buy pampas grass in most California cities: I had a nursery worker tell me recently that true pampas grass (Cortaderia selloana) wasn't invasive, that it was pampas grass' close cousin C. jubata that was causing all the problems. Jubata grass is hellaciously invasive, to be sure, but selloana is reasonably destructive in its own right.

And then there are the aquatics. Water hyacinth (Eichhornia crassipes) is sold not just in nurseries but in pet stores as well, as an aquarium plant. Go boating in the Delta near Stockton to see the results of that: Water hyacinth is widely considered the world's worst weed. Anacharis, a popular "seaweed" also sold in nurseries and pet stores, chokes freshwater lakes and streams from San Francisco Bay to the San Jacinto range.

Some plants in the invasive rogues' gallery might be surprising to the average gardener. Foxglove, for instance, which reseeds daintily in your average flower garden, becomes positively aggressive in moist meadows such as those in the Sierra Nevada or along coastal streams. Ficus carica, the popular fig tree, invades the Central Valley's riparian forests -- one of the state's most threatened ecosystems. The refined cotoneaster, a popular shrub in formal landscapes, has escaped cultivation in a number of places along the coast and is thought to pose a potential threat to the native toyon.

I suppose some nurseries could be excused for not knowing foxglove and cotoneaster are invasive. But there's not a nursery worker in the state who shouldn't know that broom and pampas grass, ivy and vinca major are threats to the landscape. And still they're sold, no warnings, no labels, no need to sign a waiver in case your neighbors sue you for unleashing the hounds of horticultural hell on their properties.

There oughtta be a law. I mean that literally.

I imagine some people will make the argument that gardeners have the right to plant what they want in their own yards, and that the state has no right to interfere.

We all, I would hope, recognize that we have no God-given right to dump oil down the storm drain. A moment of convenience for the oil changer translates into thousands of dollars' worth of damage to streams, bay and wildlife for each quart of oil. It's a pretty straightforward equation.

Well, planting invasive plants is also pollution. It's as if your quart of motor oil multiplied in the Bay, becoming several thousand barrels in a decade's time.

Plant broom, and you release the seeds of environmental destruction. Sell broom, and you profit from the demise of the native California landscape. If an auto-parts store sold motor oil whose label bore the directions "discard used oil in Bay," who would complain if that chain were penalized, or even closed down?

Many ethical nurseries refuse to sell the worst of the invasive plants. They don't seem to have lost any business as a result. No broom, no pampas grass, no tamarisk or arundo, and they still seem to be able to make ends meet.

I don't think it's asking too much for the good folks in the state Capitol -- and I suspect there are some -- to make it illegal to sell the worst of the invasive plants. And if nursery owners are concerned by that prospect, perhaps they could forestall such legislation by labeling such plants as "highly invasive," and suggesting their customers try something else instead. They could even come up with a voluntary certification program. Wouldn't you buy from a nursery certified "invasive-free"?

Chris Clarke is a garden and nature writer who lives in Pinole. He also is editor of Faultline Magazine on state environmental news; see www.faultline.org. E-mail him at irascible@faultline.org.