If a landscape design calls for tropical plant species, one cannot go wrong with including Hibiscus rosa-sinensis. Its genus, Hibiscus, is part of its common name, Chinese hibiscus or tropical hibiscus, but all too often this is the plant people simply call hibiscus. The flowers are large, bold, and prolific, always a bright spot during their long, all summer bloom season.
We had one as a foundation planting at my childhood home in Palo Alto. Bright red. Reliable. Located in a raised brick planter with southern exposure, it endured heat all day through the summer. Through winter, it still thrived except for some frost damage at its tips and a few dropped leaves, even when it snowed in 1976. I remember walking to school that day, taking my time, enjoying the unusually white landscape for my Bay Area hometown. And still the tropical hibiscus continued to flourish as soon as the weather warmed in spring.
One of the reasons why it might have performed so well was indeed that southern exposure keeping it just warm enough on cold days, a slight house eve providing further protection. This is how Colonial Williamsburg is able to grow pomegranates, as I mentioned observing them planted against a south-facing brick wall. This hibiscus also thrived and bloomed during hot summers with little additional irrigation. In fact, we did not have irrigation in that planter, so how could it manage with highly irregular hand watering? As a foundation planting, its roots grew under the house slab where the soil was cool and moist. This part of Palo Alto at one time was marshy, right adjacent to Matadero Creek. Consequently, there was and is a high water table. Given the clay soil, water was readily accessible.
How do I know about the high water table? After that snowfall in '76, we experienced a drought, prompting Dad to dig a well, by hand, so we could water our garden. He only needed to dig to 22' before tapping the aquifer below. Did we ever use it? No, the hand pump became more of a novelty than a practicality. Still, that is how I understood our water table, and why our slab house always shifted with the changes in weather. But I digress.
Hibiscus are available in bold colors and white, single and double flowers. Growers will train them as standards, but they naturally are multi-stemmed shrub forms. The photo below of the double red standard was taken at Thomas Jefferson's Monticello, highlighting our former president's interest in exotic plants to grow on a terrace in the summer, then move them into a greenhouse or solarium over winter. In many parts of the country, hibiscus are grown as an indoor plant, but since we are in California, we can grow them outdoors, year-round in most places. They are not as drought tolerant as other shrubs, so their use should be limited. Yet if the right conditions exist, as in my personal example tucked close to a home on a high water table, then watering could be a non-issue. An example of why landscape architects and designers can benefit from a thorough site analysis, to take advantage of those idiosyncrasies (we might say microclimates), found on sites.
Botanical Name: Hibiscus rosa-sinensis
Hibiscus: Greek, hibiskos, a vernacular name closely associated with marshmallow. The Royal Horticulture Society also suggests the name may come from ibiskum for a plant that would live in the regions associated with the bird, ibis (p.155).
Rosa-sinensis: Rose of China
Common Name: Chinese hibiscus, tropical hibiscus
Family Name: Malvaceae
Origin: Southeastern Asia
Positioning: Background, foundation (smaller cultivars), planters
Garden Themes: Tropical, pollinator, courtyard/patio, coastal
Uses: Border, screen, informal hedge, topiary, accent, container, espalier, screen
Type: Evergreen shrub
Form: Upright, round to arching if left unpruned
Size: 10' tall by 8' wide (cultivars will vary; can reach 30' tall in Hawaii)
Outstanding Feature(s): Flower
Stem: Slightly red turning light brown to gray with maturity
Shape: Ovate (high variability)
Color: Dark green (variegated cultivars)
Surface: Glabrous, glossy
Flower: Summer. Large, showy, single or double, funnel-shaped with prominent stigma. White and shades of pink, red, yellow, and orange. Flowers may only last one day but are prolific. Edible
Fruit: Autumn. Inconspicuous brown capsule.
cultural requirements, tolerances & problems
Sunset Zones: 9, 12-16, 19-24; H1, H2
USDA Zones: 9-12
Light: Sun to light partial shade
WUCOLS SF Bay Area Hydro Zone: Moderate
Texture: Sand, loam, clay
Moisture Retention: Evenly moist with minor, periodic dryness
pH: Acidic to slightly alkaline
Tolerances: Mild drought
Branch Strength: Medium
Insects: Mealybugs, spider mites, aphids, scales, thrips
Disease: Leaf spot, canker, chlorosis, armillaria, phytophthora, root rot
citations & attributions
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Bodine, A. (2018, November 28) "Homemade Insecticidal Soap for Hibiscus Plants." SFGate, San Francisco. Accessed on September 4, 2021, from https://homeguides.sfgate.com/homemade-insecticidal-soap-hibiscus-plants-91610.html.
Extension Gardener. "Hibiscus rosa-sinensis." North Carolina State University, Raleigh. Accessed on September 4, 2021 from https://plants.ces.ncsu.edu/plants/hibiscus-rosa-sinensis/.
Gillman, E.F. (1999, October). "Hibiscus rosa-sinensis." University of Florida Cooperative Extension, Gainesville. Accessed on September 4, 2021, from https://hort.ifas.ufl.edu/shrubs/HIBROSA.PDF.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
Plant Finder. "Hibiscus rosa-sinensis." Missouri Botanical Garden, St. Louis. Accessed on September 4, 2021, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=282563.
SelecTree. UFEI. "Hibiscus rosa-sinensis Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on September 4, 2021, from https://selectree.calpoly.edu/tree-detail/153.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on July 27, 2021.
All other photos by TELCS.