How Did Trees Come to San Diego?
From sagebrush to an urban forest
As a resident of six years, if you were to ask me to list things I associate with San Diego, California, I’d say: cliffside beaches, clear water, blue skies, and eucalyptus trees galore. Seriously, if you’ve visited this city, you’ll know what I’m talking about. From my desk, I can look out my window and see five one-hundred-foot eucalyptus trees on my block.
Because of this fact, you’d be excused for thinking San Diego a lush city, but it hasn’t always been this green. In fact, this SoCal city started out as a dusty Spanish mission between semi-arid mesas.1 Early descriptions of 19th-century San Diego often mention a landscape of dirt roads and sparse vegetation, mostly coastal scrub and sagebrush. Not much changed when San Diego became part of the United States in 1850.
The climate of Southern California is Mediterranean semi-desert, with mild winters and very little rain, so dense native forests never formed here. As the San Diego Floral Association noted, early San Diego homes were surrounded with “bare dirt and a few struggling plants.” Early city planners had big dreams, though. In 1868, civic leaders set aside 1,400 acres of scrubland under the name “City Park” (what we now call Balboa Park), envisioning that this barren mesa overlooking downtown could someday be a great urban park. For years, however, the “park” remained nothing but dry chaparral and dirt. Locals even grazed cattle there.
By the 1880s and 1890s, San Diego’s boosters realized the city needed more greenery to attract residents and visitors. Other cities in Southern California were planting trees along streets and establishing lush parks, so why not San Diego? The challenge, of course, was water (a recurring theme in San Diego’s history) and finding tree species that could survive the dry summers. A few enterprising residents began experimenting with planting non-native trees that might handle the climate. Notably, some early imports included the California pepper tree (actually from Peru) and eucalyptus from Australia – hardy species that grew quickly. Yet it wasn’t until a determined horticulturist named Kate Sessions came along that San Diego’s transformation from brown to green truly took off.
The “Mother of Balboa Park” and Her Experimental Forest
Kate Sessions (1857-1940), often called “the Mother of Balboa Park,” arrived in San Diego from Northern California in 1883. A horticulturalist and landscape architect, Sessions quickly developed a passion for greening the city.
In 1892, Sessions struck a deal with the City: she would lease 30 acres in City Park for her commercial nursery in exchange for planting 100 park trees per year and giving San Diego’s government an additional 300 per year.2 At that time City Park was mostly barren ground, so the idea was transformative. Sessions got to work, importing seeds and saplings from around the world to test in San Diego’s soil. Soon, cypress, cork oak, camphor, pepper trees, rubber trees, and eucalyptus saplings—many grown from seeds she sourced globally—began dotting the park’s landscape. Thanks to her, nearly all the oldest large trees in Balboa Park today were planted in that era.
Sessions was nothing if not adventurous in her plant choices. She traveled as far as Baja California in 1900 to find new species. “I dug from the field five small palms… and brought them to San Diego… Later a few thousands seeds were planted,” Sessions wrote in the California Garden publication. The palms she referred to were the San José Hesper Palm (Brahea brandegeei), which she subsequently planted by the hundreds in Balboa Park’s Cabrillo Canyon. Many of those palms still thrive today, forming a picturesque palm grove at the park’s western approach. She also famously introduced the city to the jacaranda, a subtropical tree from South America (and one of my personal favorites) that dazzles each spring with purple blossoms—in fact, the jacaranda is now the official urban tree of the City of San Diego. (If you brave San Diego in the gloomy months of May and June, you can experience the “purple haze” of jacaranda blooming across San Diego’s neighborhoods.)
Perhaps Kate Sessions’ greatest contribution, beyond the specific species, was fostering a culture of horticulture in a place where it had been lacking. She co-founded the San Diego Floral Association in 1907 to teach locals how to grow ornamentals and garden. Neighborhoods like Mission Hills and North Park soon benefited from her nursery stock—acacias, palms, pines, and more—which she proved could thrive in San Diego’s climate. By the time of the 1915 Panama-California Exposition in Balboa Park, Sessions’ vision had literally taken root: a lush, green space that impressed the millions of expo visitors and put San Diego on the map.
Trial and Error—Which Trees Took Root (and Which Didn’t)
Greening a semi-arid city was not without challenges. Early horticulturists like Sessions had to experiment to find trees that could handle San Diego’s mild winters, dry summers, and occasional strong winds. Many of her choices proved brilliant—Canary Island palms, Mexican fan palms, and many other palm species thrived with moderate watering. Aleppo pines and cypress grew well on the park’s mesas, and pepper trees provided quick shade along dusty roads. The beloved jacaranda, once exotic, took so well to San Diego that it’s now ubiquitous. Sessions even successfully cultivated oaks and wildflowers native to other parts of California.
However, not every tree was a perfect fit. One notable lesson came from the aforementioned eucalyptus. Sessions and others planted thousands of fast-growing Tasmanian blue gum eucalyptus around San Diego in the late 19th and early 20th centuries, hoping to create quick shade and even use them for timber. The trees did grow rapidly, but over time they revealed downsides. These Australian imports proved too well-adapted—invasively so, crowding out native plants. Their oily wood and dropped bark also pose a fire hazard in the dry climate. (Tasmanian blue gums were one of the primary culprits in spreading the deadly wildfires in Los Angeles earlier this year.) It doesn’t take much searching online to find a litany of anti-eucalyptus rants from San Diegans.
Water was, and remains, another constraint. Some tree species that looked promising (e.g., maples and elms) failed simply due to lack of moisture. Historical records mention that certain imported trees withered during drought years or had to be removed because they drank more water than the city could afford. Over time, the city adjusted by planting hardy, drought-tolerant varieties in public areas—think olive trees, stone pines, and citrus—and saving thirstier trees for spots that could be well-irrigated (like Balboa Park’s cultivated gardens).
Despite the setbacks and a few failed experiments, San Diego in the mid-20th century was now shaded by canopies of palms, pines, and flowering trees, from downtown all the way to outlying neighborhoods.
Today’s Urban Forest in San Diego
Fast forward to today, and San Diego’s urban forest is a vital part of the city’s identity. Strolling through areas like Balboa Park, Bankers Hill, or Point Loma, you’ll find mature trees everywhere—an urban canopy that is the legacy of those early greening efforts. In 2017, it was estimated that the City of San Diego had around 4.9 million trees in total across streets, parks, canyons, and private yards. Among these, the most common species include some interesting mixes of natives and imports: Chinese banyan (ficus) trees shade many older streets, arroyo willows thrive near creek beds, Japanese cheesewood (an ornamental tree) pops up in yards, Aleppo pines from the Mediterranean still stand tall, and petite pygmy date palms adorn countless gardens. San Diego counts about 12,000 jacarandas lining its streets and parks. And perhaps most emblematic of Southern California, the Mexican fan palms tower over homes and line many streets in the city.
Maintaining an urban forest in a big city is no small feat. The City of San Diego’s Urban Forestry Program now manages over 250,000 street trees planted along roads and in public rights-of-way. City arborists and community groups work together on tree planting events, mindful of increasing tree canopy in underserved areas. (San Diego’s overall tree canopy coverage is about 13% of the city’s area—still relatively low, so there’s a big push to plant more.) New initiatives like the “Free Tree” program even let residents request a street tree to be planted in front of their home, part of the city’s climate action goals to expand urban greenery. The spirit of Kate Sessions lives on in these modern efforts. San Diego’s urban forest is a human-made forest, grown tree by tree, story by story.
Iris Engstrand, San Diego: California’s Cornerstone, (San Diego: Sunbelt Publications, 2005), 50.
Engstrand, San Diego, 115.