Nestled in a corner of Golden Gate Park is an unlikely slice of tropical rain forest.
Each morning, thick fog shrouds its trees and shrubs, snuggling them with moisture. As the fog lifts, a wonderland of flowers appears. Regular heavy mist makes these plants happy. They may come from close to the equator, but they grow best when temperatures hover around 60 to 70 degrees.
Just like an autumn day in San Francisco.
Vaguely familiar but exotic, these blooms look like they were plucked out of Dr. Seuss fantasies. Giant lavender powder puffs buzz with bees. Cosmos-like magenta dahlias cover small trees. Draped from trail-side bushes, golden teardrops hang like jeweled earrings.
By noon, dew lines pine needles like shiny crystals, slowly dripping to the earth. The shaggy needles hang downward to ease the water’s steady flow, an adaptation to rain forest’s constant damp. Clouds of monarch butterflies flutter over mammoth white sunflowers stretching 40 feet tall.
This microclimate in the San Francisco Botanical Garden turns out to be the perfect paradise for tropical plants, native to the mountains of Mexico and Central America.
Called the Mesoamerican Cloud Forest, this unusual collection is a rare opportunity to see these mountain beauties – especially considering its near sea-level location. Used to cool clouds in their native mountain climates, they thrive on San Francisco fog near the bay.
“These plants grow at 5,000 foot elevation or higher where they’re constantly in the clouds,” explained Don Mahoney, curator of the San Francisco Botanical Garden. “The cloud bank is like perpetual fog.
“These plants love a cold summer,” he added, “so San Francisco is perfect for them.”
One of only a handful worldwide, this curated cloud forest is at its peak of bloom.
“Out of the 700 species we have planted here, only about 10 bloom in spring,” Mahoney said. “October through January is when these plants bloom.”
Maps make it easy to traverse the forest’s miles of trails and identify many plants. But bring mosquito repellant; the bugs like it here, too.
As part of its current “Cloud Forest Experience,” the botanical garden developed a new app to help with plant identification.
Some of the plants are endangered or extinct in the wild. Mahoney points to the jaw-dropping Deppea splendens – those dazzling 3-inch-long golden earrings with the ruby red calyx cap – as a prime example. The original specimen was collected as seed by Bay Area botanist Dennis Breedlove in 1973 in the mountains of southern Mexico.
A member of the coffee family, this shrub easily reaches 6 to 8 feet in San Francisco; in Mexico, it could be double that size. This distinctive species grew wild in only one location that anyone knew about. When Breedlove returned to the same site in 1986, Deppea had vanished, the victim of farmland development. Now believed extinct in the wild, Deppea splendens ranks among the rarest flowers in cultivation today.
“We’re preserving this flower for generations to come,” Mahoney said. “Some day, it may be reintroduced into the wild. Hummingbirds certainly like it.”
Such rarities dot the Cloud Forest. A 3-foot-tall begonia with daisylike flowers pops out of the shade. A blanket of bright orange gesneriads (the same family as African violets) covers a slope.
Planted on a terraced hillside, the Cloud Forest takes up only about 21/2 acres of the 55-acre botanical garden complex. This site started as a grove of cypress trees, planted more than a century ago. For decades, camellias and magnolias occupied the cypress shade.
Mahoney envisioned the grove as a perfect place to try something different. The conversion started about 30 years ago. “Fortunately, cloud forests feature many magnolias,” he said.
The cypress trees, now towering more than 200 feet, form the top canopy for the rain forest below.
“Cloud forests have five distinct layers,” Mahoney explained. “We mimic that.”
Oaks and pines, many more than 100 feet tall, form the second layer. Under those giants, smaller shade-loving trees, topping out at about 30 or 40 feet, thrive in the third layer’s dappled sun.
At home in deeper shade, flowering shrubs and perennials create a fourth layer. With no sun, ground covers soak up moisture at the base of the rainforest in the fifth and bottom layer.
Mahoney became enchanted by cloud forests when he took a trip to Mexico with Breedlove, curator of the California Academy of Sciences.
“You’re up 3,000 feet,” Mahoney recalled. “Every bend, there’s a waterfall and you drive right under the falls or over the falls on metal gratings. It was absolutely scary.” But when they stopped to look at the rain forest, Mahoney was awestruck.
“Bamboo and ferns grew so thick, you couldn’t walk,” he said. “The debris (from trees) on the ground was 8 feet thick; if you fell into it, no one would find you. So, we stuck to the road.”
But they kept finding plants like they’d never seen before. “Dennis Breedlove was responsible for collecting lots of plants (for this garden),” Mahoney added. “Back in the 1970s, he brought in thousands of specimens for UC Berkeley’s botanical garden, our garden in San Francisco and the Huntington (in Pasadena). If it wasn’t for him, some of these plants would be totally gone.”
Many plants tantalize with their familiarity but surprise with unexpected size and colors.
“There are more than a hundred species of salvia in the cloud forest,” said Mahoney, noting the blooms in colors from near-black blue-purples to lipstick red to nearly neon lime green. Salvias, such as the blue-vine sage, pop up around every corner on the trails.
“The signature plant is the fuchsia,” Mahoney noted. “Fuchsia microphylla, the little leaf fuchsia in particular. It grows like a weed. If you see fuchsias, you know you’re in cloud forest.”
The tree dahlia (Dahlia imperialis) is a “mini,” only 12 feet tall. In Central America, it tops 20 feet.
The plants grow shorter by design. “In the true cloud forest, they get 300-plus inches of rain a year,” Mahoney said. “We don’t give them anywhere near that much. If we did, you’d need a machete to walk the trails.”
Likewise, the “world’s tallest sunflowers” stay in the manageable 30- to 40-foot range; in Central America, they reach 70 feet. Anywhere they find them, Monarch butterflies can’t resist.
“They’re the same food source the Monarchs feed on (in Mexico) before they migrate to California,” Mahoney said. “They feel right at home.”
Also indicative of cloud forest are bromeliads and orchids. Although the garden has reintroduced some colorful bromeliads, orchids became rare in this display; not because they wouldn’t grow, but some visitors coveted them too much.
“People kept walking off with them,” Mahoney said. Warren Roberts, superintendent emeritus of the UC Davis Arboretum, loves San Francisco’s Cloud Forest.
“San Francisco is probably the best place in California to create a cloud forest,” Roberts said. “The city has a perfect blend of cloud, or fog, and cool weather but almost no frost, just the right amount of heat, and good water.
“And the Cloud Forest is in a shady and out-of-the-wind corner of the botanical garden,” he added.
Over the decades, Roberts contributed some rare shrubs and trees to the Cloud Forest collection. He knows they’ll grow better there than in the UC Davis Arboretum, or elsewhere in the Central Valley.
“The farther away we get from the Golden Gate, the less likely that we would be successful in creating an outdoor tropical highland cloud forest,” he said.
This fall, thousands of visitors will trek through the Cloud Forest. “You can spend a lot of time wandering the trails,” said Mahoney, who walks those paths every day. “It takes about four hours to see everything. But even an hour is worth it.”