Cool Blue Blooms of Fall

plumbago (Plumbago auriculata)

plumbago (Plumbago auriculata)

And so, in the end, it has been left to the cool blue blooms of November to finally grant us a reprieve from the die-hard summer of ’96. Until a few days ago, it seemed that this summer, regardless of what the calendar said, would never, ever truly go away.
The cape plumbago (Plumbago auriculata), especially, has been our saving grace. In Los Angeles, the powder-blue flowers of this plant are the freeway traveler’s companion each fall. New England aristocrats may boast of burnished autumn leaves, yet their brilliant coloration depends on chilly weather. Our more plebeian plumbaginous pleasure is, at least, predictable.
Did I say plebeian? There is a cultivar of plumbago known as Royal Cape whose flowers are a deep, majestic blue. A long, mounding hedge of it may be observed near the entrance to the Los Angeles County Arboretum in Arcadia. A white-flowered cultivar of this plant is also available.
A closely related species with true blue flowers is the dwarf plumbago (Ceratostigma plumbaginoides). Native to the mountains of western China, this is an extremely hardy, foot-tall ground cover whose leaves turn red in the fall. Other Ceratostigma species, with similar characteristics, may occasionally be found in local nurseries.
Three sages with blue flowers are blooming now. My favorite is Guatemalan blue sage (Salvia cacaliifolia), with fresh light green, almost succulent, triangular leaves and matchless sky-blue flowers. Unlike most sages, this one needs protection from the sun, but grows out nicely from the shade provided by a tall shrub or small tree. Like other tropical ornamentals – hibiscus, canna and princess flower come to mind – Guatemalan sage grows best with its feet in the shade and its head in the sun. Salvia chamaedryoides is a trailing sage with gray leaves and blue flowers. The mealy cup sage, Salvia farinacea, is familiar to bedding plant enthusiasts; it is one of the few annuals that blooms in blue.
The outstanding blue flowering annual, of course, is lobelia. The cultivar Crystal Palace is royal blue, while Cambridge Blue has pale blue flowers the color of our freeway plumbago. Lobelia is the ideal edging plant, growing no more than 6 inches tall.
Borage (Borago officinalis) is a self-sowing annual with light-blue star flowers; it is just starting to bloom. Its leaves are edible and have the flavor of cucumber. Be careful that you eat only the very young seedling leaves fresh; older leaves are somewhat prickly and will stick in your throat unless they are cooked prior to consumption.
Blue daze (Evolvulus glomeratus) is a strong ground cover with miniature, sky-blue, morning-glory flowers. It grows well in eastern exposures or wherever ivy geraniums flourish.
Blue butterfly (Clerodendrum ugadense) is one of those subtle shrubs that will catch the eye of children and their grandparents, even as the middle generation hustles on by. Its blooms are neither loud, nor numerous, nor long-lasting enough to win the approval of calculating flower watchers. Yet its appeal is undeniable when you stop and take a second look. Its flowers are meticulously crafted, two-tone blue miniatures, resembling – in truth – a troop of tropical butterflies.
From casual observation, it is apparent that blue flowers tend to look their best in combination with pink and/or violet ones. Borage nicely offsets Queen Elizabeth roses, and dwarf plumbago looks fine against a background of Mexican sage (Salvia leucantha). Blue daze grows in perfect harmony with pink Balcon ivy geraniums. Red may also be a fitting companion, as is illustrated by a tapestry hedge of bottlebrush (Callistemon citrinus) and cape plumbago.
A mimosa mix: George Frankie of Studio City writes: “I have received some mimosa (Albizia julibrissin) seeds that I would like to germinate.
Because of the hard shell of the seed, I would appreciate your advice on how to increase the chances of germination.”
Like the seeds of many leguminous trees, those of the mimosa or silk tree have hard seedcoats (you call them shells) that create a physical barrier to germination. This characteristic allows such trees to survive periods of drought but prevents us from easily germinating them. In “Seeds of Woody Plants in the United States,” published by the U.S. Forest Service, the following two preplanting treatments for mimosa seeds are given: Scarify (scar the seedcoat with a file), then soak seed in sulfuric acid for 15 minutes – be careful, this stuff burns! – and finally soak seed in water for an additional 15 minutes. Or, put seed in boiling water, remove water from heat source and allow seed to soak for 24 hours.
Tip of the Week: The mimosa or silk tree is a good choice for those who want a fast-growing, flowering shade tree that doesn’t get too big. In Los Angeles, the silk tree generally grows to about 30 feet tall with equal spread. November is an excellent month for planting silk trees.

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