Tree
Texas Mountain Laurel
Dermatophyllum secundiflorum · Fabaceae
Also called: Mescal Bean, Mountain Laurel, Frijolito
Texas Mountain Laurel (Dermatophyllum secundiflorum) is a low-water tree well suited to Tucson and the low desert. It's a slow-growing tree.
Texas Mountain Laurel at a glance
- Water use
- Low (established)
- Sun
- Full sun to light/reflected shade
- Mature size
- 10-15 ft H x 8-10 ft W (slowly; can reach 25 ft in age). Often grown as a large shrub or small multi-trunk tree.
- Growth rate
- Slow
- Bloom
- Violet to purple (occasionally white cultivars), intensely grape-soda fragrant, Early spring (February-April)
- Cold hardiness
- Hardy to about 10 F; USDA zones 8-11
- Soil
- Requires very well-drained alkaline soils; tolerates rocky, caliche, and limestone soils. Will not tolerate wet or poorly drained sites.
- Native range
- South-central Texas and northern Mexico (Chihuahuan Desert/Edwards Plateau); not native to the Sonoran Desert, but well adapted to Tucson
- Best used as
- Specimen/accent, Evergreen screen or large shrub, Patio/courtyard tree, Spring-blooming focal point
- Wildlife
- Fragrant flowers attract bees and other pollinators; it is the larval host for the Genista broom moth (Sophora worm), which can defoliate new growth in spring. Birds use the dense evergreen cover.
- Toxicity
- Highly toxic—the bright red seeds (mescal beans) contain the alkaloid cytisine and are poisonous if the hard seed coat is chewed/broken and ingested; keep away from children and pets.
How to grow Texas Mountain Laurel in Tucson & the low desert
Watering
Drought tolerant once established; water deeply but infrequently, about every 2-3 weeks in summer heat and rarely in winter. Overwatering and poor drainage cause decline and chlorosis.
Fertilizer & nutrients
Low fertilizer needs; nitrogen-fixing legume. If foliage yellows (chlorosis) in alkaline soil, treat with chelated iron rather than heavy nitrogen feeding. Avoid overfertilizing.
Pruning & care
Prune lightly just after spring bloom to shape and to train into tree form by removing lower branches; it is slow to recover, so prune minimally. Remove seed pods if desired for tidiness/safety.
Notes
Evergreen, with glossy dark-green compound leaves and showy fragrant purple wisteria-like flower clusters in early spring, followed by hard silvery woody pods containing red toxic seeds. Very slow-growing but long-lived and tough. Watch for Genista moth caterpillars on new growth. Formerly Sophora secundiflora / Calia secundiflora.
Sources: AMWUA 'Landscape Plants for the Arizona Desert'; University of Arizona Cooperative Extension; Arizona-Sonora Desert Museum; Tohono Chul / Tucson Botanical Gardens references