Showstoppers from the south

IN Los Angeles, where good looks matter and even our gardens can seem like red carpets dotted with botanical starlets, flowering trees vie for their share of attention. They bloom in pretty pinks, elegant whites, regal purples. This year’s biggest star: the floss silk tree, its canopy a gown of vivid orchid-like blossoms.

The tree, native to Brazil and Argentina, is giving its best performance in years, admirers say. And although those flowers are starting to drop, other trees are lined up for their turn. More than a dozen flowering species -- equally dazzling and also hailing from south of the equator -- do well in Southern California gardens. Think bright yellow acacias, blue-purple jacarandas and scarlet coral trees.

How have these imports from the Southern Hemisphere stolen the show?

For humans, the trees are eye candy -- a spectacle of color, pure and simple. For trees, beauty is a strategy for survival.

Jim Folsom, director of the Huntington Botanical Gardens in San Marino, says most of these trees hail from mixed forests. Because they are scattered throughout the forest, they must declare themselves boldly to bees, birds, butterflies and other pollinators moving from one tree to the next. The effect: a profusion of flowers, brightly hued and rich in nectar and pollen. For optimal exposure, many bloom on leafless branches at the end of a dry season.

The “brilliance” of this process, Folsom says, is that the same kind of tree throughout a forest will flower at the same time -- when conditions are most favorable for seed ripening and germination. “There’s great pressure for synchrony,” he says.

Flowering is triggered by changes in temperature, rainfall and day length, but scientists are still learning the nuances of what makes these trees tick.

Jacarandas, which are native to Argentina and Brazil, typically bloom by June, but Folsom says they may flower (or grow new foliage) any time of year in reaction to light, heat, rain or pruning.

The pink floss silk tree, Chorisia speciosa, usually blooms before its less common white-flowered cousin, C. insignis. The two trees usually blossom in sequence between August and November, but this year they flowered in tandem in late September -- and both were extraordinary. What tweaked them, July’s record heat or some other condition? Experts can only speculate.

Specimens in public landscapes and urban residential gardens are particularly colorful, Folsom says, because they are offspring of the showiest forest trees, selected and propagated by horticulturists for their abundant flowers.

In home gardens, natives of the Southern Hemisphere can straddle the seasons with color. These subtropical and semitropical trees (see list) share one trait: They love heat. Take the golden trumpet tree, often used to line streets. It blooms gloriously when grown inland but rarely flowers by the ocean.

Some, however, are cold-sensitive and too risky for inland gardens. Die-hards will try them in protected niches, on sun-baked walls or in containers that can be moved to warm spots in winter. The African tulip tree (Spathodea campanulata) is a good example -- a fast grower with huge cupped orange or yellow flowers. You’ll find specimens flowering on a frost-free knoll at the L.A. County Arboretum and Botanic Garden in Arcadia.

Patience, however, is as important as planning. Most of these trees are grown from seed and may not flower for five to 10 years. The firewheel tree (Stenocarpus sinuatus) won’t bloom for a decade.

“It’s one of my favorite trees,” says the Huntington’s curator of living collections, Kathy Musial. “It’s extremely slow-growing but really worth the wait.”

Once mature, this Australian tree sports spidery red and orange flowers in waves from summer into winter. The large-lobed foliage looks like giant shiny oak leaves -- a feature to appreciate while you’re waiting for the flowers.

Many of these splendid Southern Hemisphere trees have grown in these parts for more than a century, thanks to the efforts of late horticulturists who helped to define the California landscape: Francesco Franceschi and Peter Riedel of Santa Barbara; Kate Sessions of San Diego; Hugh Evans of Santa Monica and his sons Jack, Morgan and Bernard; and Samuel Ayres of La Canada Flintridge.

Decades after these folks shaped the scenery, new additions are forthcoming. Expect more trumpet trees, including the much-admired apricot-colored hybrid from the L.A. County Arboretum. The staff there also is evaluating a chubby seedling of the floss silk tree that is flowering when the specimen is only 15 feet tall instead of the customary 25 to 30 feet.

Jo O’Connell of Australian Native Plants Nursery in Ventura is pushing her favorite acacia: A. merinthophora, a weeper “like Rapunzel’s hair with yellow flowers.” She also likes Banksia integrifolia for its long-lasting, bright yellow flowers.

Chris Barnhill, curator of plant collections at the Fullerton Arboretum, is a big fan of South African drought-tolerant trees. He’d like to see the pink-clustered pompon tree (Dais cotinifolia) in home gardens, and he thinks the blue-violet tree wisteria (Bolusanthus speciosus) could give jacaranda a run for its money.

One thing is sure: Gardeners in this region dig color -- especially exotic, on high and en masse. So bring on the trees.

Lili Singer can be reached at home@latimes.com.

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Know before you grow

Flowering trees from the Southern Hemisphere make bold seasonal statements in the landscape. Follow these guidelines when planning:

Selection: Do your homework. Large trees need wide berths. Smaller ones fit in tight spaces; a few will even grow in pots. Some species thrive inland; others are best near the coast.

Placement: Most of these trees want fast-draining soil. Some need full sun; others are OK in light shade. Consider leaf drop and, more important, flower drop. Certain blossoms (jacaranda included) are slippery and sticky and can stain pavement.

Planting: Transplant these coldsensitive trees in spring or summer but not in fall. Moved now, they may rot during winter.

Watering, feeding: Though some species are drought-tolerant, all young trees need regular irrigation and a thick layer of mulch to insulate roots and conserve moisture. Feeding needs vary by species, so check with your nursery.

Pruning: Prune these trees after flowering, as needed. Timing may vary between species and from year to year. Some, such as the floss silk tree, are best left untouched; pruning destroys the natural symmetry.

-- Lili Singer

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Favorites

Coral tree, left, Erythrina humeana ‘Raja.’

Firewheel tree, below left, Stenocarpus sinuatus.

Floss silk, Chorisia speciosa (pink) and C. insignis (white).

Cape chestnut, Calodendrum capense. Tall, broad. Pink flowers.

Strawberry snowball, Dombeya cacuminum. Grows fast and tall.

Sweetshade, Hymenosporum flavum, and coral gum, Eucalyptus torquata, both from Australia. Mid-size, narrow, good for tight spaces.

Snow-in-summer, Melaleuca linariifolia, Australia. Round-headed.

Australian flame tree, Brachychiton acerifolius, and Queensland lacebark, B. discolor. Good in pots.

Golden trumpet tree, Tabebuia chrysotricha. Soaks up inland sun but rarely flowers by the ocean.

-- Lili Singer