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Gardening hangovers, Part 3: fountain grass

April 21, 2010 |  7:05 am
Invasive_FountainGrass Grasses are among California’s most prolific weeds. Exotic bromes and other annual grasses now carpet millions of acres, displacing of native wildflowers, bunch grasses and shrubs.

Most arrived with 19th century settlers and livestock (as contaminants in feed or lodged in animals’ coats, for example). But in recent years, ornamental grasses have joined the fray.

“Grasses are useful in a landscape,” says Jim Folsom, director of botanical gardens at the Huntington, “but by nature they are invasive; being a grass generally means being able to cover a lot territory fast.”

A nasty example festers at Arcadia Wilderness Park. Three acres of a steep, dry slope are bristling with a billowy plant with fuzzy seed heads, called fountain grass (Pennisetum setaceum). This runaway garden plant is also slurping up water in a nearby stream bed. Drew Ready of the nonprofit Los Angeles and San Gabriel Rivers Watershed Council says it’s converted “a biologically diverse stand of chaparral” into “a biological wasteland.”

The grass’ bad seed gets around easily — roving perhaps miles in strong wind. It has most likely already plopped into the adjacent Angeles National Forest, and needs only a disturbance -- fire or mudslide — to spread rapidly.

Like other alien grasses, fountain grass makes wildlands more fire-prone. “It provides a layer of really fine fuel that ignites very easily,” Ready explains. Coupled with an increase in human-sparked fires, exotic grasses threaten to extirpate plant communities on Southern California’s hillsides, including rare coastal sage scrub habitats. “Native species can’t endure these frequent fires and die off,” says Ileene Anderson, biologist with the Center for Biological Diversity.

In an attempt to keep fountain grass from escaping gardens, horticulturists have selected cultivars that aren’t supposed to reproduce, including purple-colored ‘Rubrum.’ But Ready doesn’t think they’re a safe bet: “Most nurserymen will tell you they’re not always sterile.” 

Ready advises gardeners to avoid all fountain grasses. “There are so many safe and beautiful alternatives,” he says, listing native deer grass, blue oat grass and "Canyon Prince" wild rye as examples.

He’s also concerned about the recent popularity of Mexican feathergrass; “because it spreads so readily by seed, it’s at best a garden nuisance; at worst it will become as much of a scourge as fountain grass.”

The Watershed Council promotes alternatives to the region’s most invasive plants on its Weed Watch website.

-- Ilsa Setziol

Coming Thursday: acacia


Gardening hangovers, Part 2: Mexican fan palms

Gardening hangovers, Part 1: periwinkle

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Photo credit: Ricardo DeAratanha / Los Angeles Times