Spring in
the Sonoran desert officially begins with an
incredible show of brilliant
yellow flowers
opening on the Blue Palo Verde (Cercidium floridum). These
flowers appear in March or April and may persist into June,
turning the naturally rounded blue green canopy of the trees
into giant yellow floral arrangements. Smooth blue green bark
and a dense highly divided branching pattern form a greenish
backdrop for this floral display.
The
Blue Palo Verde is native to the American Southwest and
Northern Mexico, including Baja California and is distributed
from sea level to four thousand feet elevation. This tree is
well adapted to extreme desert
heat yet is hardy
to 10 to 15 degrees Fahrenheit. Mature trees grow to twenty five
to thirty feet in height, and twenty five to thirty five feet in
width. The pale blue green bark can carry on photosynthesis when
the tree has lost its leaves to cold weather or drought
conditions. The unique color, bright flowers, ample shade and
moderate growth rate make Blue Palo Verdes a highly desirable
and popular landscape tree.
These trees are commonly used in a
variety of landscape settings. They are often used as a theme
tree in streetscapes, as an accent tree at focal points or entry
areas, and as a transitional tree where new landscape
construction integrates with surrounding native desert. In their
natural desert setting the Blue Palo Verdes grow like large
shrubs with branches extending all the way to the ground. In
landscapes they are typically pruned into a low branching or
multiple trunk form. They can however be pruned into single
trunk shade trees.
Pruning
trees to
develop shape and form is best done when the trees are
relatively young and small in stature. Once the desired shape is
achieved very minimal seasonal pruning is needed. The fine leaf
litter and shade from this tree affords an understory area where
many ground covers, flowers and shrubs can thrive. Most
residential landscapes will accommodate one to two mature Blue
Palo Verdes per yard area.
Blue
Palo Verdes will tolerate an array of soil types and
planting conditions,
but do best in well draining sandy soils. Planting in turf areas
requires careful irrigation management particularly if the lawn
is overseeded with winter grass. Water and fertilizer are
applied to winter lawns during the time of year when Palo Verdes
are essentially dormant. These winter irrigations create soil
conditions conducive to the development of root rot. Established
trees can be naturalized
(gradually weaned from supplemental irrigation) to survive on
seasonal rainfall but will be more lush and vigorous with
regular irrigation. A general recommendation is for two deep
soaking irrigations per month for established trees during
summer months.
Mites
can attack these trees causing witches’-broom" a dense
production of small branches arising in a small area along the
branch. Mistletoe can also infest these trees. The
witches’-broom" and mistletoe can be controlled with pruning.
The
Palo Verde Root
Borer
is the only lethal pest but it tends to attack only stressed or
declining trees. The best protection from borers is to keep
trees vigorous and generally healthy.
The
Blue Palo Verde is yet another example of a Sonoran desert
tree that brings bright flowers, shade and graceful texture into
any
landscape. The design community continues to tap the landscape
uses of this durable, adaptable and beautiful tree.
