Ironwood

Frost Tolerance: Deciduous if the temperature drops below 28°F (-2°C), mature trees killed at 15°F (-9°C)

Heat Tolerance: Excellent

Sun Exposure: Full sun, tolerates reflected heat

Origin: Sonoran desert in Arizona (USA) and Mexico (Sonora, Baja California, Baja California Sur)

Growth Habits: Evergreen tree or large shrub, growing slowly up to 15 to 30 feet tall (4.5-9 m), 15 to 25 feet wide (4.5-7.5 m); older trees have trunks that can reach 2 feet in diameter (60 cm); twigs with paired thorns, 0.12 to 0.4 inch long (3-10 mm), at each node; pinnately compound leaves, up to 2.4 inches long (6 cm) with 6 to 20 oval gray-green, thick, leaflets, 0.28 to 0.8 inch long (7-20 mm)

Watering Needs: Little to no water once established, grows faster and looks better with some occasional deep waterings

Propagation: Seeds, that need scarification (fresh seeds will grow without scarification)

Ironwood (Olneya tesota), U.S.D.A. Forest Service Collection, Courtesy of the Hunt Institute

Blooming Habits:
Short lasting but showy lavender flowers, 0.24 to 0.6 inch wide (6-15 mm), covering the tree in masses of blossom, in the spring.

Fruiting Habits:
Seeds pods with 1 to 4 edible seeds

Culture:
Some maintenance is needed to train the trunk in a tree shape. There is also some litter generated with the flowers and pods. It is still an excellent tree for the Phoenix area.