Is So Cal a Desert?

The following is a draft of an article I am preparing for the California Native Plant Society (CNPS) – San Gabriel Mountains Chapter newsletter.

Enjoying the wildflower display in Anza Borrego, March 2008.

From Wild Suburbia

Q. We get so little rain here that it seems like it is a desert. Do we live in a desert?

A. Our chapter of CNPS covers both the San Gabriel Valley and Mountains. This region and much of coastal California are defined by a unique mediterranean climate. Although we do not have high levels of annual precipitation, it is the pattern of rainfall that is so unusual. Nearly all of our rain, which averages 18 inches per year but is quite variable in time and space, comes during mild winter months. We share this climate – hot, dry summers, and cool, wet winters – with four other regions of the world. It comprises less than three percent of the world’s surface, but offers a high level of plant diversity.

Returning to the question, there are two major differences that are important for gardeners to know when considering growing desert plants. First of all, we generally receive more annual precipitation, but more importantly, we get it in the winter. Desert plants can do very well in our climate, especially during times of low annual rainfall. Cold, wet, El Nino winters, when they occur, can be very difficult for these plants. This is especially true in gardens with heavy loam or clay soil that stays wet for long periods. A desert garden may thrive for many years in our mediterranean climate, only to rot out during El Nino.

The second important difference between local deserts and scrubland areas is that deserts sometimes get heavy bursts of rain during the summer. Although there may be very little accumulation, desert plants are adapted to this condition and respond quickly to the rain, often with an outbreak of riotous flowers. Chaparral and scrub plants do not expect, nor appreciate much summer rain. In fact some, like the notorious flannel bush (Fremontodendron californicum), can not accept any. I grow fragrant evening primrose (Oenothera caespitosa) in my garden in South Pasadena. Occurring in Great Basin and Desert Provinces of eastern California, it requires very little water, but responds to a summer soaking with a massive floral display. Since my garden has heavy loam soil, the plant typically lasts about three years before burning itself out.

Sphinx spider on fragrant evening primrose (Oenothera caespitosa) blooming in my garden in late May 2006.

From Wild Suburbia

Q. Are there any desert plants, other than cactus, that can be grown in my garden and what do I need to do to keep them healthy?

A. Beginning with the second part of the question first, desert plants will do better if you have well-drained soil. Amending soil is a tricky business that we don’t recommend. If you have heavy soil, consider using desert plants in containers and sticking to plants that are adapted to your soil type. Be sure to provide very little additional water, only several times each year. Do not amend, fertilize or enrich the soil. If you are going to mulch your garden, use inorganic material such as decomposed granite, gravel, pebbles, or rocks.

Desert Museum palo verde (Parkinsonia ‘Desert Museum’), a three-way cross, provides shade and color in late May in the Cultivar Garden at Rancho Santa Ana Botanic Garden.

From Wild Suburbia

Some of the plants that are found in desert washes make excellent garden specimens. Two trees in this category are: palo verde (Parkinsonia florida), and desert willow (Chilopsis linearis). The palo verde’s striking yellow flowers appear in late spring, while the showy pink trumpet-shaped flowers of the desert willow grace the garden in mid summer.

Desert willow (Chilopsis linearis ‘Regal’) blooming in late June.

From Wild Suburbia

Indian mallow (Abutilon palmeri) is a delightful shrub from the southern reaches of the state that has fuzzy, gray leaves with flowers the color of the soft drink Tang®. It blooms profusely throughout the spring and intermittently all year long.

Orange flowers of Indian mallow (Abutilon palmeri) contrast with its soft gray leaves.

From Wild Suburbia

Desert mallow (Sphaeralcea ambigua) is a subshrub with long flowering stems. In the wild the flowers are typically apricot-colored, but the cultivar, Louis Hamilton, has cherry red blossoms. This plant flowers in the spring and can be cut back after it blooms. Both the desert and Indian mallows will reseed in the garden.

Louis Hamilton desert mallow (Sphaeralcea ambigua ‘Louis Hamilton’) at RSABG.

From Wild Suburbia

And finally, I would be remiss if I didn’t call out at least one desert bunch grass. Alkali sacaton (Sporobolus airoides) is a warm-season grass that looks similar to deergrass (Muhlenbergia rigens) except that it has an airy, delicate inflorescence.

There are many other desert plants well suited to our gardens. Consult the California Classics Plant List on the Rancho Santa Ana Botanic Garden website (www.rsabg.org) for more suggestions.