Garden Oracle / Drought and Heat Tolerant Gardening / Tucson - Phoenix - Arizona - California

Growing Gossypium harknessii:
San Marcos Hibiscus

social icons Facebook Twitter Pinterest Instagram

Form: A rounded shrub.
Lifespan: Perennial.
Leaf retention: Evergreen in regions without freezes, otherwise deciduous.
Growth rate: Moderate.
Mature Size: 2-4' high and 5-6' wide.
Flowers: Large, pale yellow to white petals, forming a cup, with five red dots inside, enclose yellow stamens at the center.
Bloom: Spring through fall.
Fruit: A four-chambered woody pod containing seeds covered with 1/8" long filaments, resembling tiny cotton balls.
Leaves: Heart-shaped, glossy green, thick, nearly succulent, with five veins radiating from the base.
Stems: Sprawling, thick, gray-brown, somewhat brittle, no thorns.
Roots: Most likely a taproot and many lateral roots, similar to other closely related members.
Wildlife: The flowers attract butterflies and moths. It is a larval food plant for Painted Lady and Gray Hairstreak butterflies and several moth species.
Toxic / Danger: No.
Origin: Baja California, Mexico.

Cultivation and Uses
USDA hardiness zones: 9b-11. This plant freezes to the ground at 25°F but is root hardy to 20°F.
Heat tolerant: Yes.
Drought tolerant: Yes.
Sun: Full sun. Shade limits plant growth.
Planting: Place in full sun in a location where cold air does not collect in the winter. Make sure that the soil drains well, is low in organic content, and unamended.
Soil: Well drained, dry, low in organic content. This plant is salt tolerant and loves heat and poor soil. Never apply organic soil amendments and never fertilize.
Water after becoming established: Deep water every 2-4 weeks in warm months, allowing for rain. Too much water results in leggy growth. Too little water results in sparse leaves.
Mulch: Never. Organic mulch, when rained on, supplies nutrients harmful to the plant.
First Year Care: Protect from freezing.
Prune: Remove freeze damage after the danger of frost is past. At other times, minimally trim to keep in bounds.
Litter: Low, except for hard freezes.
Propagation: Seed.
Uses: Ornamental.

Gossypium harknessii is a wild cotton and a member of the Mallow family (Malvaceae). It is related to the domesticated cotton species G. hirsutum – American / Mexican cotton, and G. barbadense – Egyptian cotton.

Do you have additional information or a different experience for these plants that you would like to share? Email All contributions are welcome and appreciated.

Gossypium harknessii: San Marcos Hibiscus flower

Gossypium harknessii: San Marcos Hibiscus seed capsule

Gossypium harknessii: San Marcos Hibiscus

© 2008-2023 by
Latest update: October, 2021