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Gardening hangovers, Part 2: Mexican fan palms

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


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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The City has installed grates at stormwater inlets to prevent trash from flowing into that system and out to sea. But sand and silt collect in front of the grates and now Washingtonia robusta seeds are germinating in these little oases....little W. robusta farms on every street corner.

I thought the very tall skinny ones were from north Africa.

The Watershed Council has mapped 6000+ mature Mexican Fan Palm trees in LA and San Gabriel River watershed wildlands. Most of them are infesting areas adjacent to rivers and streams in the urban wildland interface, with many many large infestations found in low lying areas and near highly irrigated landscapes where water collects.

We use high resolution aerial photography with field checks to assure accuracy. There are far more trees too small to be visible or in the understory that we don't have the resources to map but our work has defined the most impacted areas. These maps allow partnering agencies to begin to prioritize removal and control.

In urban areas we too have seen Mexican fan palms clogging storm drains resulting in flooded streets and they are they are frequently a strain on resources for public works and parks maintenance crews who have to spend limited resources removing seedlings and discarded palm fronds.

As noted, palm alternatives exist. California fan palm (Washingtonia filifera) is a great street tree alternative in inland areas. Where a little more space is available or for accent trees, Blue hesper (Brahea armata) and Guadalupe Island fan (Brahea edulis) are beautiful alternatives. Reuben Ellis of Ellis Farms Inc. (http://www.ellisfarms.com/) has also suggested the Pindo palm (Butia capitata) and Mediterranean fan palm (Chamaerops humilis).

Thanks to the Times for making space for a well written critique of current garden practices. We're looking forward to more!

Here are some popping out of a storm drain, a common occurrence in Los Angeles. The day before I snapped these photos half the street was flooded; so much for these things being benign in urban areas.



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