Tree
Palo Blanco
Mariosousa willardiana · Fabaceae
Also called: White-bark Acacia, Whitebark Acacia
Palo Blanco (Mariosousa willardiana) is a low-water tree well suited to Tucson and the low desert. It grows to 18-25 ft H x 10-15 ft W in full sun, with a moderate growth rate.
Palo Blanco at a glance
- Water use
- Low (established)
- Sun
- Full sun
- Mature size
- 18-25 ft H x 10-15 ft W
- Growth rate
- Moderate
- Bloom
- Creamy white to pale yellow, fragrant catkin-like spikes, Spring (April-May), sometimes again after summer rains
- Cold hardiness
- Hardy to about 24-25 F; USDA zones 9b-11 (frost-sensitive when young)
- Soil
- Requires excellent drainage; thrives in sandy, rocky, well-drained desert soils. Intolerant of poorly drained or overwatered sites.
- Native range
- Sonora, Mexico (Sonoran Desert region of Mexico); native to the broader Sonoran Desert in Mexico but not to Arizona
- Best used as
- Specimen/accent tree, Patio tree, Narrow/courtyard spaces, Filtered-shade tree
- Wildlife
- Flowers attract bees and pollinators; provides light bird cover.
- Toxicity
- No significant toxicity reported.
How to grow Palo Blanco in Tucson & the low desert
Watering
Deep, infrequent irrigation; water established trees deeply about every 2-4 weeks in summer. Overwatering causes weak growth and root problems—keep it lean.
Fertilizer & nutrients
Little to no fertilizer needed; nitrogen-fixing legume. Avoid heavy feeding, which promotes weak, floppy growth.
Pruning & care
Prune lightly in warm season to develop the multi-trunk or single-trunk form and reveal the ornamental white bark; remove only crossing or dead wood. Minimal pruning preserves its delicate character. Protect from frost the first few winters.
Notes
Prized for its striking smooth, peeling chalky-white to cream-colored bark and airy, weeping, finely divided foliage casting light filtered shade. Semi-evergreen to drought/cold-deciduous. Narrow footprint ideal for tight spaces and courtyards. Formerly classified as Acacia willardiana (also referenced as Mariosousa heterophylla). Frost-tender when young—site in a warm microclimate in Tucson.
Sources: AMWUA 'Landscape Plants for the Arizona Desert'; Arizona-Sonora Desert Museum; University of Arizona Cooperative Extension; Water Use It Wisely / AMWUA plant profiles