Palo Verdes in Landscape Settings
It's easy, when thinking of Palo Verdes in the landscape, to lump them together based on their physical similarities to each other. Overall this is a reasonable assumption but there are subtle differences between the various species and, now numerous, hybrids. Placement in the landscape, establishment practices, irrigation, understory plantings and interactions with pedestrians set some Palo Verdes apart from others. The most popular Palo Verdes include, Blue (Parkinsonia Cercidium floridum), Sonoran (Parkinsonia Cercidium praecox ‘AZT’), Parkinsonia Cercidium Hybrid ‘AZT’ (Parkinsonia Cercidium Hybrid ‘AZT’), Desert Museum (Parkinsonia Cercidium Hybrid ‘Desert Museum’) and Foothill (Parkinsonia Cercidium microphyllum). All are highly valued for their distinctive southwestern structure and appearance, their spring flower display and their durability in an array of landscape applications.
Cold hardiness varies within the Palo Verde species from 18 to 10 degrees F. Local and regional, historic low temperatures should be considered, as well as the duration of freezing conditions, when selecting which Palo Verdes to plant and in your locations.
Because of their spectacular spring flower display, Palo Verdes are often used in entry features, streetscape plantings or as individual or grouped specimens. All are well adapted to these uses. Flower displays are further enhanced with Sonoran (Cercidium praecox ‘AZT’), Cercidium Hybrid ‘AZT’ (Cercidium Hybrid ‘AZT’), Desert Museum (Parkinsonia Cercidium Hybrid ‘Desert Museum’) as these varieties are cloned (grown from cuttings rather than seed) so all trees within the variety bloom at the same time and for the same duration. The effect is stunning. All species, when mature, will generate substantial shade that can reduce the growth and flowering of understory plantings.
Establishing Blue and Foothill Palo Verdes requires some care. As the most rustic (least domesticated) Palo Verdes their growth rate is relatively modest making it easy to overwater recently transplanted trees. Establishment can be further complicated by extensive understory plantings of shrubs or turf, especially turf that is over-seeded in fall and winter. Over-seeding is typically done in early fall and requires frequent application of water to establish winter lawns. This practice comes at a time when these Palo Verdes are beginning to head into their “dormancy” and their demand for additional water is especially low. Root damage caused by this seasonal over irrigation may not be observed until the following spring when these trees break bud and begin a new seasonal growth cycle. Once established in the landscape, these Palo Verdes are extremely durable and can better tolerate periodic overwatering.
The ‘Desert Museum’ presents a slightly different challenge. Both empirical and observational data suggest that one of the parents of this hybrid is Parkinsonia aculeate, a tree noted for its rapid growth when water and fertilizer are readily available. The irrigation demands of understory shrub and turf plantings can encourage rapid, excessive top growth that can quickly outgrow root development. Trees can become wind throw risks or grow far larger than the original landscape design intended and require significantly more pruning. Parkinsonia Cercidium Hybrid ‘AZT’ has Parkinsonia Cercidium praecox, as one of its observed parents, which appears to reduce the growth response to the application of excess water and nitrogen. The bark remains green and smooth as trees mature and branch angles are more open, like those enjoyed in Sonoran Palo Verde.
Pedestrian issues have two primary components: intrusive branches and thorns. Thorns are always a consideration when placing thorned desert species in the landscape. The Palo Verde Hybrids eliminate this challenge by producing no thorns. Blue and Foothill have modest thorns on new and intermediate branches. Placement of these trees near pedestrian area requires care and seasonal pruning, as they mature. Such measures help minimize issues associated with thorns and low hanging branches.
As the Arizona State tree, Blue Palo Verdes are an emblem of the southwestern desert, making it and its related Palo Verde species and hybrids essential centerpieces of landscapes that reflect the special beauty of our surroundings. Their durability and adaptability make them remarkably well suited for landscapes in Arizona, Nevada, Texas and California. Their flowers and shade make them welcome everywhere.