By Susan Lewitt, for Let’s Talk Plants! August 2024.
Do You Know This About Ceanothus?
Look for the wonderful California Native Plant Society’s native plant sale, on October 19, two months from now. It’s a great opportunity to add native plants for your landscaping, including ceanothus species. Ceanothus is a great plant for people’s yards because they help with soil fertility by partnering with Frankia, a microorganism that also is associated with other native plant species. The Frankia nodules on the roots take nitrogen from the air, and turn it into ammonia. Small amounts of ammonia in the soil help the soil microorganisms, and allow plants to utilize soil nutrients more efficiently, keeping them healthy.
“The plant-mycorrhiza-frankia (tripartite) relationship often becomes a multi-layered community of associated free-living and plant-related organisms that protect and support each other. The relationships are complex with only the most obvious presently recognized. The different associated organisms are responsible for root hormones, pathogen control, nematode control, root exploration, plant community resource sharing, mineral mining, water retention and many more.” (“Frankia is an actinomycete bacteria that commonly occurs on Ceanothus and many other native species”, https://www.laspilitas.com/classes/Frankia.html)
In their natural settings Ceanothus may live at least 50 to 100 years. Without Frankia, the life sustaining organism, Ceanothus, and other plant species might be short-lived. To help your Ceanothus, other native plants, and associated microorganisms thrive, weedy plants and other unwanted life forms need to be eliminated. Also, don’t make the mistake of fertilizing Ceanothus. They may seem to respond at first and then suddenly die due to the presence of damaging pathogens. With that said, there are several Ceanothus species that do well in San Diego including the following ones.
Nodules of Frankia on Ceanothus roots (left and middle photos, courtesy of Las Pilitas Nursery). These are good because they help keep native plants, like this Hairy Ceanothus, Ceanothus oliganthus, on the right, healthy. (Right photo courtesy of Calscape.)
Buck Brush, Ceanothus cuneatus, is a Ceanothus that is well represented in the wilds of California. Look for its white flowers in the spring, which are sometimes tinted blue or lavender. Since this plant easily hybridizes with other similar plants, its size and appearance may vary. Generally, this evergreen plant is up to 12’ tall by 12’ wide with a pleasing scent and may also flower in the winter and summer. Its rounded spreading form works for bank stabilization and hedges. It needs very little water once established and prefers fast draining soil, and full sun. In Chaparral, Pinyon-Juniper Woodland, or Yellow Pine Forests, Buck Brush may be found growing near Oneneedle Pinyon Pine, Pinus monophylla, Ponderosa Pine, Pinus ponderosa, Foothill Pine, Pinus sabiniana, Blue Oak, Quercus douglasii, Johnny Jump Up, Viola pedunculata, Manzanita, Arctostaphylos spp., and Coffeeberry, Frangula spp. It is known to support caterpillars, butterflies, and moths, including the Salt-and-Pepper Geometer (Biston betularia).
Buck Brush Ceanothus (left and middle) could be visited by the Salt and Pepper Geometer, which may be too well camouflaged to spot. Left and middle photos courtesy of Calscape. Right photo courtesy of Creativecommons.org/publicdomain/zero/1.0/
Hoaryleaf Ceanothus, Ceanothus crassifolius, an upright shrub, is abundant in the lower elevations of the coastal mountains in Southern California, and also Baja, California. Its tiny white flower clusters, seen in winter and spring, are sometimes tinged with yellow or pink. It may grow as large as 14’ high and 10’ wide. It will grow in full sun to partial shade, in fast draining soil and needs very little water in the summer. Companion plants include Bush Poppy, Dendromecon rigida, Thickleaf Yerba Santa, Eriodictyon crassifolium, Toyon, Heteromeles arbutifolia, Scrub Oak, Quercus berberidifolia, and Hollyleaf Cherry, Prunus ilicifolia, in areas of Chaparral, Pinyon-Juniper Woodland, and Yellow Pine Forest. It is enjoyed by birds, bees, butterflies and caterpillars.
Hoaryleaf Ceanothus, Ceanothus Crassifolius, will make a nice addition to any garden, especially a native garden. Top photos courtesy of Calscape. Bottom photos by Keir Morse.
Chaparral Whitethorn, Ceanothus leucodermis, another abundant Ceanothus found in the wild, occurs in California and Baja, California, especially in coastal and inland mountain habitats, such as chaparral, coniferous forest, and oak woodland. Its growth, at a maximum of 13” tall by 7’ wide, is rounded, upright or columnar with winter to spring flowers that may be blue, lavender, purple, and white. It will do well in full sun to partial shade in fast draining soil. It is associated with other Ceanothus such as Woollyleaf Ceanothus, Ceanothus tomentosus, Hoaryleaf Ceanothus, Ceanothus crassifolius, plus Scrub oak species, and Spiny Redberry, Rhamnus crocea. It supports caterpillars, butterflies and moths, including the Brown Elfin and the Ceanothus Silkmoth.
Chaparral Whitethorn adds a splash of lavender and blue to your garden. Left and right photos courtesy of Calscape. Middle photo by Keir Morse.
Hairy Ceanothus, Ceanothus oliganthus, is a winter and spring flowering shrub that does well without summer watering, in fast or medium draining soil, and will give you a pleasant fragrance with its blue and purple flowers. This mounding shrub may get up to 10’ tall by 12’ wide. It may be found on rocky slopes facing the coast in Chaparral, foothill Woodland and Yellow Pine Forest. Its many compatible plants include Purple Sage, Salvia leucophylla, Sticky Monkeyflower, Diplacus aurantiacus, California Sagebrush, Artemisia californica, Deerweed, Acmispon glaber, Brittlebush, Encelia spp., Sage, Salvia spp., Manzanita, Arctostaphylos spp., Oaks, Quercus spp., Lodgepole Pine, Pinus contorta, Ponderosa Pine, Pinus ponderosa, Red Fir, Abies magnifica, Yucca species, native grasses, and Dudleya species. It supports caterpillars and butterflies including Lorquin's Admiral (Limenitis lorquini).
Hairy Ceanothus (left and right) is attractive and gets beautiful visitors, like this Lorquin's Admiral (Limenitis lorquini, middle). Left photo courtesy of Calscape, Middle photo by O, no rights reserved, Right photo by Keir Morse.
White Coast Ceanothus, Ceanothus verrucosus, is a rare species with a limited range. Its black, cream and white flowers are displayed during the winter and spring. This evergreen shrub with a slight fragrance is smaller than the others, reaching a maximum of 10’ tall by 8’ wide. Full sun with fast or medium draining soil and a once-a-month watering in the summer once established will meet its needs. It occurs in the Chaparral, usually southern maritime chaparral, on dry hills, canyons, marine terraces and coastal bluffs. Many other native plants make good companions for it including Laurel Sumac, Malosma laurina, Black Sage, Salvia mellifera, Woollyleaf Ceanothus, Ceanothus tomentosus, Torrey Pine, Pinus torreyana ssp. torreyana, Del Mar Manzanita, Arctostaphylos glandulosa ssp. crassifolia, Summer Holly, Comarostaphylis diversifolia ssp. planifolia, Chamise, Adenostoma fasciculatum var. fasciculatum, San Diego Sage, Salvia munzii, Encinitas Baccharis, Baccharis vanessae, Nuttall's Scrub Oak, Quercus dumosa, Bush Rue, Cneoridium dumosum. Caterpillars, and Butterflies including the Brown Elfin, rely on this plant.
White Coast Ceanothus (left and right photos) support pollinators like this charming, Brown Elfin, (middle photo) Right and left photos courtesy of Calscape. Middle courtesy of Creativecommons.org/publicdomain/zero/1.0/
Plants that I highlight in my articles including these Ceanothus (and other Ceanothus not mentioned), are recommended for the San Diego area by Calscape and are usually found at nurseries and the CNPS plant sale, but availability will vary from year to year. When looking for landscaping choices, you may narrow down the plant choices by looking up Calscape, then entering your zip code, address, or the name of your area where you want to landscape, because there are over 8,000 native plants in California and of those, more than 700 live in San Diego.
Resources and References:
The California Native Landscape: The Homeowner’s Design Guide to Restoring Its Beauty and Balance by Greg Rubin and Lucy Warren, Timber Press, Portland, Oregon 2013
Ceanothus, https://en.wikipedia.org/wiki/Ceanothus
“Frankia is an actinomycete bacteria that commonly occurs on Ceanothus and many other native species”, Las Pilitas Nursey, https://www.laspilitas.com/classes/Frankia.html
“Is Ammonia Good for Plants: The Impact on Plant Health” By Glen Chandler -June 11, 2024 https://plantamerica.com/is-ammonia-good-for-plants/
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