Tree · Sonoran native
Ironwood
Olneya tesota · Fabaceae
Also called: Desert Ironwood, Palo Fierro, Tesota
Ironwood (Olneya tesota) is a very low-water tree native to the Sonoran Desert region well suited to Tucson and the low desert. It grows to 15-30 ft H x 15-30 ft W in full sun, with a slow growth rate.
Ironwood at a glance
- Water use
- Very Low (established)
- Sun
- Full sun
- Mature size
- 15-30 ft H x 15-30 ft W
- Growth rate
- Slow
- Bloom
- Pale lavender to pinkish-purple (pea-like flowers), Late spring (May-June); flowering intensity varies year to year
- Cold hardiness
- Cold-tender; foliage damaged near 20 F and prolonged hard freezes can kill young trees. USDA zone 9-11 (best in warm microclimates within Tucson).
- Soil
- Well-drained desert soils, including rocky, gravelly, and alkaline soils; excellent drainage is essential. Intolerant of wet, poorly drained sites.
- Native range
- Sonoran Desert of southern Arizona, southeastern California, and northwestern Mexico (Sonora, Baja California). A Sonoran Desert endemic and indicator species.
- Best used as
- Long-lived evergreen specimen and shade tree, Nurse plant / keystone tree in native and habitat landscapes, Wildlife gardens and naturalized Sonoran designs
- Wildlife
- Keystone Sonoran Desert 'nurse plant' that shelters seedlings of cactus and other species; flowers are a major spring nectar source for native bees and other pollinators; seeds eaten by birds, rodents, and other wildlife; provides critical nesting and cover habitat. Larval host for desert insects.
- Toxicity
- Not toxic to humans; raw seeds were roasted and eaten by Indigenous peoples. Bears spines, especially on young growth. Dense wood is prized for carving.
How to grow Ironwood in Tucson & the low desert
Watering
Extremely drought tolerant and survives on rainfall once established. To improve establishment and modestly speed its slow growth, water deeply about once a month in summer; little to no supplemental water needed in cooler months. Avoid overwatering.
Fertilizer & nutrients
Not needed; nitrogen-fixing legume adapted to lean desert soils. Fertilizer is generally unnecessary and can promote frost-tender growth.
Pruning & care
Prune sparingly in late spring/early summer (after frost danger) to shape and lift the canopy and remove dead or crossing wood; minimal pruning suits its naturally dense, evergreen form. Wood is extremely hard and dense.
Notes
Among the longest-lived Sonoran Desert trees (can exceed 100-200+ years). Semi-evergreen, dropping leaves briefly before bloom or in drought/cold. A protected native in Arizona; slow growth and frost sensitivity mean it should be sited in a warm, well-drained spot. Iconic, high-value habitat tree.
Sources: Arizona-Sonora Desert Museum; AMWUA "Landscape Plants for the Arizona Desert"; University of Arizona Cooperative Extension; Water Use It Wisely; SouthwestDesertFlora.com