By Susan Lewitt.
Pick up a postcard of San Diego. What do you see besides iconic landmarks? Mexican Fan Palms, Washingtonia robusta, Canary Island Date Palms, Phoenix canariensis, and a few other palm species which are non-native invasive plants not representative of the wonderfully diverse San Diego native plant community! When I walk around my neighborhood, I see evidence of the Mexican Fan Palms trying to take over, with seedlings popping up everywhere, especially within 100 yards of the parent tree. Birds will disperse their seeds even further. They’re easy to remove when they first sprout, but if ignored, become much harder to pull out. Left alone, they spread to undeveloped natural areas, displacing natives.
These palms aren’t just overly prolific, but will hybridize with the California Fan Palm, Washingtonia filifera. If overwatered, they develop root rot. They are subject to Gandoderma butt rot, only cured by removing the infected plants, and Thielaviopis trunk rot, affecting young plants that have had their leaves ripped off improperly. Fan Palms can have borer infestations. They also hold onto their leaves forming a dry skirt or thatch of dead leaves, which is a fire hazard, and creates a haven for rats, and snakes. As they grow taller, it can be expensive to hire a professional for leaf removal. Their mature thorny massive size makes them a poor choice for yards unless they are professionally trimmed.
Several non-native palms recommended by the California Invasive Plant Council (CAL-IPC), but not by CNPS, are the King Palm, Archotophoenix alexandrae, which is frost sensitive, Pindo palms, aka Jelly palms, Butia capitate, the Mediterranean Fan Palm, Chamaerops humilis, the Guadalupe Palm, Brahea edulis and the Chilean Wine Palm, Jubaea chilensis. The Blue Hesper Palm, Brahea armata, also recommended by CAL-IPC, is sometimes sold at CNPS plant sales. Other nursery Palms include the Queen Palm and the Date palm which are not recommended by CNPS. Although the California Fan Palm, Washingtonia filifera, is a native that supports some of the native fauna, it is seen also as a poor landscaping choice.
So, how about some nice trees, like the Coast Live Oak, Quercus agrifolia? These oaks may obtain a height of 25 to 82 ft tall and a width of 35 feet with a sizable trunk. Currently, I am growing one in my curb strip near some native grass, two Scrub Oaks and a Eucalyptus tree. Other good companion plants as understory or neighbors are Coyote Brush, California Buckwheat, Coast Sagebrush, Toyon, California Coffeeberry, Woolly Bluecurls, Snapdragon Penstemon, Fuchsia-flowering Gooseberry, California Wild Rose, Manzanita ssp, Ceanothus ssp, Salvia ssp, and annual wildflowers such as Poppy ssp. and Chinese Houses. My Coast Live Oak is roughly 4 years old and has obtained a height of almost 4 feet tall with its last growth spurt of over 18 inches since this past January. As it matures it may attract quite a few native birds, mammals, reptiles and invertebrates. Some of the pollinators I hope it will attract include the California Sister, the Propertius Duskywing, the Polyphemus Moth, the California Oak Moth and the Oak Winter Highflier Moth. It does well in full sun, to part shade, with low moisture, and a maximum of once-a-month summertime watering when established. It tolerates a variety of soils but prefers well-draining loam. It is evergreen, but will drop leaves on a continuing basis which enrich the soil around it.
Hollyleaf Cherry, Prunus ilicifolia ssp. ilicifolia is another good choice attracting many birds and some mammals to its fruit. It is the host plant for Western Tiger Swallowtails, Pale Tiger Swallowtails, Elegant Sphinx Moths, Epinolia Iomonana, Lorquin’s Admirals, and California Hairstreaks. This plant does well with quite a few trees and other plants, including Manzanita, Barberry, Ceanothus ssp., Toyon, Bushmallow, Pine ssp., Oak ssp., Flannelbush, Currant ssp., plus more. It grows up to 50’ tall by 20’ wide, accepting full sun to part shade and very low moisture. It should be watered no more than once a month in summertime when mature, preferring medium- to fast-draining coarse soil. Cream and white colored flowers appear from winter to spring.
As you have read, most palms are not ideal for landscaping, but native trees such as the Coast Live Oak and the Hollyleaf Cherry, especially when planted alongside other natives, are excellent choices, enhancing San Diego’s biodiversity by attracting and supporting our native wildlife. For more information on these trees and other plants that work well for your area, please visit Calscape and enter your zip code. (https://www.calscape.org/)
