Southern California Climate
Southern California is made up of six counties: Los Angeles, Orange, San Bernardino, Riverside, Ventura and Imperial. It is a complex area influenced by the Pacific Ocean and elevational changes due to mountain ranges. U.S. Department of Agriculture plant hardiness zones range from zones 10 and 11 along the coast to zone 7 at the tops of interior mountain ranges. Average annual rainfall varies from 8 inches to 30 inches depending primarily on elevation and the rain shadow effect of the mountains. Where you live in Southern California determines what type of hibiscus will survive the winter.
If you live in the warmest areas of Southern California, you can grow tropical hibiscus outdoors. Zone 10a can occasionally have winter temperatures between 30 and 35 degrees Fahrenheit, so be prepared to protect it during freezing weather. Locate tropical hibiscus in a sheltered microclimate, such as along a south-facing wall. If freeze damage occurs, wait until spring when new growth begins and prune away dead growth to where the first new bud emerges. Flowers reach up to 8 inches wide and come in most colors except blue and black. Many cultivars exist, from dwarf to tall-growing and from single to double flowers. Bushes rarely exceed more than 15 feet tall in the continental U.S. Native to Asia, tropical hibiscus is grown worldwide in tropical areas.
Hardy hibiscus are suited for growing in Southern California's interior valleys, foothills and mountains where freezing temperatures regularly occur. They prefer rich, moist soil, so growing it in more arid areas will require frequent watering during hot summer months. Confederate rose (Hibiscus mutabilis) is native to China, growing in USDA zones 7 through 9. Large, 5- to 7-inch-long leaves look somewhat like maple leaves, and single or double white to pink flowers are 3 to 5 inches wide. Common rose mallow (Hibiscus moscheutos) is native to the Southeast in USDA zones 5 through 10, growing 6 to 10 feet tall with 8-inch-wide pink, red or white flowers. Hardy hibiscus die back in the winter and regrow from perennial roots.
Both types of hibiscus are suited to container growing, which allows them to be moved onto patios, decks and other outdoor living spaces when in bloom. Move hardy hibiscus in containers indoors if temperatures are predicted to fall below 15 degrees F. Give hibiscus full sun for compact growth, although hardy hibiscus tolerates partial shade, and tropical hibiscus benefits from afternoon shade during hot summer afternoons in inland valleys. Prune tropical hibiscus in early spring to stimulate new growth, which bears the flowers, and remove faded flowers to prolong the bloom period. Give moisture-loving hardy hibiscus a layer of mulch to conserve soil moisture, and protect the tall stems from strong winds.