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Scientific: Parkinsonia florida (formerly Cercidium floridum)
Common: blue palo verde (palo verde is Spanish for green stick or log)
Family: Fabaceae (Leguminosae)
Origin: Arizona native, lower Sonoran Desert subdivision dry wash riparian tree.

Pronounciation: Par-kin-SONE-ee-a FLOR-i-da

Hardiness zones:
Sunset 10-14, 18-20
USDA 9-11

Landscape Use: Blue palo verde is an excellent wide spreading medium-sized native desert tree for large xeric landscape sites. This is NOT a street or lawn tree, nor is it suitable for planting around signage because of its naturally low and spreading crown structure.

Form & Character: Desert tree, somewhat rounded and spreading becoming open and irregular with age, intricate and netted terminal branching pattern, arid, dry.

Growth Habit: Partially deciduous, woody, perennial tree with moderately vigorous growth to 30 feet with equal to greater spread, epidermis of youger stems and branches smooth with a bluish green color (photosynthetically active) especially during summer, older trees produce a roughened and fissured phellem (bark).

Foliage/Texture: Small bluish-green, twice pinnately compound leaves without stipular spines, 2 to mostly 6 leaflets per rachis, drought deciduous during drier times of year if non-irrigated; the fine or imbricated branching patterns of small twigs and stems help to create a relatively fine to medium fine texture.

Flowers & Fruits: Clusters of lemon yellow flowers, 2 to 4 inches in size, cast the entire tree in yellow color; followed by less visible display of brown pod fruit. Fruit pods are 2 to 3 inches long.

Seasonal Color: Masses of yellow flowers in early to mid April. Also, the foliage turns a distinct bluish-green color during the summer monsoon season.

Temperature: Hardy to 20oF.

Light: Full sun only.

Soil: Tolerant

Watering: None after establishment. Supplemental irrigations greatly increase vigor and canopy density. Usually landscape specimens are larger than trees found in the desert due to landscape irrigation.

Pruning: Because of their inherent shrub-like growth habit, blue palo verde trees have a moderate to high pruning requirement. Pruning strategies include selective crown thininng (especially when young) to create a strong schaffold branch architecture and raising the crown base height to give the tree a more "urban friendly" tree form. Sometimes though well meaning 'arborists' (aka 'hort clods') get carried away and crown raise Parkinsonia excessively. Pruning wounds resulting from this are problematic and can result in bacterial wet wood disease and/or growth of many epicormic shoots (adventitious water sprouts) that will need to be removed, especially if the tree is irrigated.

Propagation: Seed, readily hybridizes with other Parkinsonia sp., grafting, and air layering.

Disease and Pests: Larvae of palo verde root borers (Derobrachus geminatus) feed on these trees. They grow up to 4 inches in length. Adult beetles are up to three and one half inches long with long antennae. No chemical treatment is effective, instead treat by promoting tree vigor. Mistletoe on Parkinsonia florida and Parkinsonia microphylla can be problematic and should be quickly removed.

Additional comments: Blue palo verde is the Arizona state tree. It attracts bees when in flower and is a habitat for birds year round. Salvage operations transplant native blue palo verde trees into landscape sites using a technique called 'side boxing'. Palo verde trees serve as nurse plants for young saguaro cacti by providing an overstory canopy, a microhabitat, which moderates the temperatures extremes of the desert by providing warmth in winter and shade in summer.

Parkinsonia hybrids: In recent years, blue palo verde has been hybridized with other Parkinsonia species to give many Parkinsonia hybrid cultivars that are presently popular landscape trees in the Phoenix area. Tree selections such as the interspecific hybrid cross cultivar 'Desert Museum' (introduced by the Arizona Sonora Desert Museum in 1981) are known for their large and prolific yellow flowers, poor, weak and failing branch and root structures, intense spring flower fall, and an outdoor carpet of flower litter. The good news now is that there are several other Parkinsonia hybrid cultivars such as the popular 'Sonoran Emerald' that are variously superior in form and habit.

Botanical background: Irish botanist Thomas Coulter was the first trained botanist to collect and identify blue palo verde. He obtained specimens near Hermosillo, Sonora in 1830.