Tree · Sonoran native
Screwbean Mesquite
Prosopis pubescens · Fabaceae
Also called: Screwbean, Tornillo, Twisted Bean
Screwbean Mesquite (Prosopis pubescens) is a low-water tree native to the Sonoran Desert region well suited to Tucson and the low desert. It thrives in full sun, with a moderate growth rate. Expect pale yellow / creamy yellow blooms spring into early summer.
Screwbean Mesquite at a glance
- Water use
- Low (established)
- Sun
- Full sun
- Mature size
- 15-25 ft H x 15-25 ft W (occasionally to 30 ft)
- Growth rate
- Moderate
- Bloom
- Pale yellow / creamy yellow, Spring into early summer (April-June), sometimes again after summer rains
- Cold hardiness
- Hardy to about 0 F; USDA zones 7-10. Deciduous in winter.
- Soil
- Deep, well-drained soils preferred; tolerates fine-textured, alkaline, and saline soils. Native to floodplains, so it benefits from occasional deep flooding.
- Native range
- Sonoran and Chihuahuan deserts of the southwestern U.S. (AZ, CA, NV, NM, TX) and northern Mexico; typically along washes, floodplains, and damp or saline bottomlands.
- Best used as
- Small shade or patio tree, Native/wildlife and riparian restoration plantings, Streetscape and naturalized desert landscapes, Specimen for distinctive tightly coiled (screw-shaped) seedpods
- Wildlife
- Flowers attract bees and other pollinators; the spiraled pods and seeds are eaten by birds, rodents, and other wildlife. Provides nesting cover and habitat. Larval/host value for desert insects.
- Toxicity
- Not considered toxic to humans; pods were a traditional food (ground into meal) for Indigenous peoples. Thorns can cause mechanical injury. Foliage is browsed by livestock.
How to grow Screwbean Mesquite in Tucson & the low desert
Watering
Unlike most desert legumes, screwbean does not naturalize on rainfall alone in the low desert; give deep supplemental irrigation every 2-4 weeks through the hot season once established, more in deep sandy soils. Water deeply and infrequently to encourage a strong root system.
Fertilizer & nutrients
Generally not needed; as a nitrogen-fixing legume it makes its own nitrogen. A single light application of balanced or slow-release fertilizer in spring can boost young trees, but mature trees rarely require feeding.
Pruning & care
Prune in late spring or summer to develop a single or multi-trunk canopy and remove low or crossing branches; avoid heavy pruning that promotes weak regrowth. Stake young trees only as needed and remove stakes early to build trunk strength.
Notes
Distinguished from other mesquites by its tightly spiraled, screw-like seedpods and smaller leaflets. Now often reclassified botanically as Strombocarpa pubescens, but Prosopis pubescens remains the widely used accepted name in horticultural references. Armed with paired spines. A good choice where a true Sonoran native mesquite is desired; less commonly grown than Chilean or velvet mesquite.
Sources: University of Arizona Cooperative Extension; Arizona-Sonora Desert Museum; Lady Bird Johnson Wildflower Center; Mountain States Wholesale Nursery; SouthwestDesertFlora.com