trees have been more instrumental in popularizing desert-adapted
trees in landscape designs than Thornless or Chilean Mesquites.
By providing abundant shade, lush green leaf canopy and graceful
fissured brown trunks, Thornless Mesquites are another of the
trees that dispelled the myth that desert landscapes were hot,
barren, spiny and uninviting.
While its horticultural characteristics and taxonomy remain
disputed, the Thornless Hybrid Mesquite is among the most
popular and widely used trees in the desert landscape palette.
As the common name indicates, trees are thornless, making them
ideal for landscape applications from re-vegetation of disturbed
desert sites to streetscapes, park plantings, commercial and
residential landscapes. The form and texture of Thornless
Hybrids blend almost seamlessly with surrounding native Sonoran
desert trees and shrubs. They are easily incorporated into urban
landscapes and are increasingly being used in more formal or
traditional landscape designs. Other uses include: as theme
trees along streets and commercial projects, as screens, wind
breaks or barrier plantings, as transition trees, in
re-vegetation projects or any landscape applications where ample
shade is desired. This mesquite is well suited for planting in
turf and non-turf areas.
At maturity, Mesquites can be up to 30 feet tall and as wide
with symmetrical, dome-shaped, spreading canopies. The foliage
is lacy and fern-like with compound leaves consisting of
anywhere from 20 to 40 leaflets. Cold hardy to 10 to 15 degrees
F, they can be planted throughout most regions of the desert
southwest. Trees are semi-deciduous, losing only a portion of
their leaves in warmer winters in the Phoenix, Arizona and Palm
Desert, California areas. Las Vegas and Tucson, Arizona will
have a little more leaf shed due to the lower winter temperature
typical of those communities. Leaves remaining through the
winter are shed rapidly in spring just prior to bud break.
In late spring, Mesquites produce yellow-green, unremarkable,
catkin-like flowers. By early summer curved and sometimes curled
tan to brown seed pods mature and are shed. With supplemental
irrigation and fertilization, Thornless Hybrids grow at a rapid
rate. Mature, established Mesquite trees can be naturalized to
survive on annual rainfall in desert soils with good water
holding capacity. Established trees are most lush and exhibit
best growth and appearance with supplemental irrigation during
the hot, dry summer months. Trees in well maintained lawn areas
will exhibit the greatest growth benefiting from the water and
fertilizer applied to the turf.
Thornless Hybrid Mesquites will tolerate an array of soil types
and growing conditions from harsh, full sun to shady bosque or
grove-like plantings. The first 2 to 3 years following
transplanting are critical in establishing a well distributed
root system. In typical landscape settings where water and
nitrogen are abundant, Mesquites can produce large dense leaf
canopies from rather limited root systems. These trees are often
easily damaged or completely uprooted by the high winds
associated with the summer rainy season.
Proper staking, seasonal pruning and regular deep irrigation
during the spring and summer help Thornless Mesquites resist the
damaging effects of high winds. Wind damage is NOT an
unavoidable horticultural shortcoming of Thornless Hybrids.
Making trees "seek out" water and nutrients, by appropriate
arrangement of irrigation emitters and application of nitrogen,
fosters the development of a more dispersed root system and
reduces the risk of wind throw.
During tree establishment, pruning to remove about 20% of the
canopy during the growing season will help promote root
development that is proportional to the shoot growth of young
trees. In areas with severe summer storms (monsoons), it is
important to complete this pruning prior to the beginning of the
storm season. Additional pruning, 3 to 4 weeks later, will
lessen the risk of wind-throw and branch damage. Removing more
than 20% of the canopy can inhibit rooting and encourage
undesired re-growth made up of dense flushes of branches and
leaves. Selective pruning will foster the development of a
symmetrical canopy with well-spaced branches. Stake
trees only when absolutely necessary and then only briefly.
A low-breaking, upright tree occupies no more room than a
standard-trunked specimen yet retains the natural wind
resistance of trees found growing native in desert settings.
Shade is a welcome addition to all deserts landscapes but can
inhibit the growth and flowering of some under-story plantings.
The shade produced by Thornless Hybrid Mesquites can range from
filtered to quite dense. Carefully consider the ultimate shade
that can be produced by these trees and the impact of that shade
on the growth and flowering of under-story plants and turf.
Since their introduction in the 1950's, horticultural
professionals have become accustomed to referring to Thornless
Mesquites as Chilean Mesquite or Prosopis chilensis.
The actual botanical name of this specie has long been a subject
of discussion. Within the landscape industry, Prosopis
chilensis, Chilean Mesquite and Thornless Mesquite have
evolved to become synonymous trade terms with only limited
botanical relevance. To avoid confusion it is advisable to
specify trees on plans as Prosopis chilensis,
"Thornless" or simply Thornless Hybrid Mesquite and avoid using
a botanical name altogether.
The increased acceptance of arid landscape trees, mesquites
included, has fostered a demand for greater uniformity in
appearance and growth characteristics. Efforts to increase
uniformity of Thornless Mesquites have tended to emphasize
vegetative/clonal propagation (rooting a small portion of the
plant). Vegetative propagation methods produce uniform trees by
limiting the genetic diversity within the propagation stock.
Genetic limitation has advantages and disadvantages. Genetic
diversity protects plant populations from devastating attacks by
injurious insects and diseases. Criteria for selecting parent
trees for clonal propagation tends to focus on the phenotype or
external features of trees. Upright branching, dense foliage,
trunk structure or rapid growth are examples of phenotypes
growers might use in selecting parent stock. Appearance alone
gives little indication of rooting habit, cold hardiness,
disease and insect resistance or adaptability to varying soil or
Seed and clonal Propagation programs must diligently and
regularly evaluate the horticultural qualities of the trees
currently in production, while continuing to look for new and
better selections to incorporate. The popularity and varied uses
of Thornless Mesquites requires that growers offer both uniform,
standard and multiple trunked trees and more
informal/native-looking specimens. Producing an assortment of
shapes and forms of Thornless Mesquites will require different
parent selections for clonal propagation.
Given the attractive physical and horticultural qualities of the
Thornless Mesquites it is little wonder they remain popular and
widely used trees. Efforts by nursery professionals to improve
the quality of trees coming to the market insure that Thornless
Mesquites will continue to meet the ever expanding uses of this
tree in desert landscape designs.