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Gardening hangovers, Part 2: Mexican fan palms

April 20, 2010 |  7:05 am
Invasive_MexicanFan When many of us think of Los Angeles, there’s a palm in the picture. That palm is likely Washingtonia robusta, the Mexican fan palm.

Mexican fans are the remarkably tall (up to 100 feet), skinny palms with fan-shaped fronds that have towered over much of the city’s built environment for more than a century. More conspicuous than stars in L.A.’s washed-out night sky, some palm constellations have even been dubbed historic-cultural monuments.

Although other palms have sneaked into the scene, Nicholas Staddon, director of new plants for Monrovia Growers, says Mexican fans are still popular and “very valuable — it’s fast-growing and has a wonderful tropical look.” No primadonna, aptly named robusta thrives in a couple square feet of dirt amid a sea of concrete, even roots in sidewalk cracks.

But the region’s palmy past is seeding trouble. “Most of the dates fall nearby,” says licensed herbicide applicator Bill Neill, “but some will eventually go down the storm drains into the river channels.”

To restore ecosystems, Neill kills aggressive weeds called invasives. He’s whacked and sprayed vast thickets of bamboo-like arundo along the Rio Hondo and San Gabriel River. When grant money is available, he also drills into the trunks of Mexican fan palms, then fills the holes with weed killer.

Left to their own devices, palm groves could shade and crowd out crucial habitat, including an unpaved, two-mile stretch of the Rio Hondo that borders Rosemead. There the river flows freely across the earth. Native willows, mule fat, elderberry and black walnut support rare birds, including the endangered least Bell’s vireo and the yellow-breasted chat.

Mexican fans also reduce the flood-control capacity of the L.A. River (and others). Any vegetation will slow water flow, but the U.S. Army Corps of Engineers rips out invasives before it touches native plants. “Willows don’t burn easily,” says Corps ecologist Carvel Bass, “but fan palms and arundo do, and they don’t contribute to the habitat in any positive way.”

Mexican fans and other weeds often get a leg up when people tinker with natural systems. Many of Southern California’s formerly intermittent streams now pulse with water year-round, creating an oasis for the palms.

On its Weed Watch website, the nonprofit Los Angeles and San Gabriel Rivers Watershed Council recommends alternatives to invasive plants, including palms such as Blue hesper (Brahea armata) and Guadalupe Island fan (Brahea edulis). Gardeners could also turn to Washingtonia filifera, the Mexican fan’s stockier, slower-growing cousin, indigenous to Southern California deserts.

Although the long-lived Mexican fans are likely to be a fixture of L.A. for some time, they and their fronded relatives may become less common. These days, city foresters favor broad-canopied trees, which offer more shade to city streets.

-- Ilsa Setziol

Coming Wednesday: Fountain grass

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Gardening hangovers, Part 3: fountain grass

Gardening hangovers, Part 1: periwinkle

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Photo credit: Brian Vander Brug / Los Angeles Times


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