Wildflower/Perennial · Sonoran native
Desert Senna
Senna covesii · Fabaceae
Also called: Coves' Cassia, Coues' Senna, Rattleweed, Rattlebox, Desert Cassia
Desert Senna (Senna covesii) is a very low-water wildflower/perennial native to the Sonoran Desert region well suited to Tucson and the low desert. It grows to 12-24 in H x 18-24 in W in full sun, with a moderate growth rate.
Desert Senna at a glance
- Water use
- Very Low (established)
- Sun
- Full sun
- Mature size
- 12-24 in H x 18-24 in W
- Growth rate
- Moderate
- Bloom
- Bright yellow to golden, with prominent brown anthers, Spring through fall (roughly March-October), flushing repeatedly after rains, especially with summer monsoons
- Cold hardiness
- Hardy to about 20-25 F (USDA zones 8-11); may freeze back in hard frost and resprouts from the woody base in spring.
- Soil
- Sandy, gravelly, or rocky well-drained desert soils; tolerates poor, alkaline soils. Sharp drainage required.
- Native range
- Native to the Sonoran and Mojave Deserts of Arizona, southeastern California, southern Nevada, and northern Baja California/Sonora, Mexico; common on desert plains and sandy washes from about 1,000-3,000 ft elevation.
- Best used as
- Native/wildlife garden, Butterfly garden, Low-water perennial border accent, Naturalized/revegetation plantings, Pollinator habitat
- Wildlife
- Important larval host plant for sulphur butterflies (cloudless sulphur and sleepy orange); flowers provide pollen for native bees. Seeds eaten by birds and small mammals.
- Toxicity
- Not generally considered significantly toxic; like many Senna species the seeds/pods may have mild laxative properties if eaten in quantity, but it poses little hazard in the landscape.
How to grow Desert Senna in Tucson & the low desert
Watering
Very drought tolerant once established; subsists largely on rainfall. In Tucson, occasional deep irrigation every 2-3 weeks in the hottest months prolongs bloom; avoid frequent or overhead watering.
Fertilizer & nutrients
Needs no fertilizer; as a legume it fixes its own nitrogen and thrives in lean native soil.
Pruning & care
Lightly shear or pinch to keep compact and encourage rebloom; remove frost-damaged stems and old seed pods in late winter to refresh the plant.
Notes
A short-lived, fine-textured native subshrub/perennial with ferny foliage that is often leafless during drought, leafing out and blooming quickly after rain. Excellent low-water filler that reseeds to maintain its presence. Pairs well with brittlebush and desert marigold.
Sources: Arizona-Sonora Desert Museum (plant care sheet, Senna covesii); University of Arizona Cooperative Extension; Southwest Desert Flora; Lady Bird Johnson Wildflower Center