Retama vs. Palo Verde Tree

Characteristics

• Most widely used in landscaping are the blue palo verde (Parkinsonia florida) and the foothill palo verde (Parkinsonia microphylla). In the wild, palo verde has branches clear to the ground. The blue palo verde lives 50 to 150 years and can reach 35 feet tall. Under cultivation, the tree is pruned to show the trunk and create space for pedestrians and traffic. Foothill palo verde is smaller and usually multistemmed, growing 20 feet tall. Retama reaches 15 to 20 feet tall. It can have a single or a multiple trunk and creates lighter shade than the blue palo verde. A hybrid of all three of these trees is widely used in landscaping. It combines the best features of all the parents and is called "Desert Museum" palo verde (Parkinsonia x "Desert Museum") since it originated at the Arizona-Sonora Desert Museum. All these trees have green branches and trunks, hence the common name "palo verde," which means "green stick" in Spanish.

Leaves and Branches

• Palo verdes have small pinnate green leaflets on short slender midribs in the spring which drop off during drought periods. The green bark of the branches takes over photosynthesis when the leaves are not present. Blue palo verde has blue-green leaves and branches, which have short spines. The foothill palo verde has yellowish-green foliage and limbs, and the retama has bright green leaves and branches equipped with long spines. The retama leaves differ from palo verde leaves. In spring a midrib 15 to 18 inches long bears 10 to 25 pairs of leaflets. The leaflets usually fall off in summer, but the midrib stays on and functions as a leaf. The trees are deciduous in winter.

Flowers

• Blue palo verde, Arizona's state tree, has large, fragrant, showy, bright-yellow flowers that completely cover the branches in mid-spring. About three weeks later the lighter yellow flowers of foothill palo verde appear. Retama has a flush of bloom in spring with showy yellow and orange-red flowers, and has occasional blooms through the summer. "Desert Museum" blooms profusely with large, bright-yellow flowers marked with red on the upper petal in spring and occasionally through the summer into fall.

Cultivation

• Once established, palo verde trees are very drought-tolerant. Give them supplemental water during the first year or two to establish strong, deep roots. Growth is fast when young and slows as the trees mature. They will grow in most soils and prefer full sun. Retama is such a vigorous grower that it can become a weed. Blue palo verde and foothill palo verde are hardy in U.S. Department of Agriculture plant hardiness zones 8a to 9. Retama and "Desert Museum" grow in USDA zones 8b to 9.