Mesquite - A Las Vegas Landscape Challenge?

Over 30 Mesquite trees in this Las Vegas parking lot were
blown over due to a strong summer wind.  Photos identify
 insufficient root development while considerable top
growth has taken place.

Mesquite – A Las Vegas Landscape Challenge?

In Southern Nevada we have been using mesquite trees in both commercial and residential landscapes for many years.  Found throughout the southwest, the mesquite is quite tolerant of Las Vegas environmental conditions.  Although there are different species, the Chilean Mesquite (Prosopis chilensis) and the Texas Honey Mesquite (Prosopis glandulosa) are most often the species of preference. 

Large beautiful mesquite trees that enhance our landscapes do not naturally occur, but are often a product of years of determination and hard work.  Mesquites do not grow naturally into upright single or multiple trunk trees with large full crowns.  In there natural environment trees are often found growing in thickets with their growth habit similar to a very large sprawling belligerent thorned shrub.  Young nursery trees require considerable training, mostly in the way of pruning and staking, to produce a saleable upright growing tree (notice all of the tree support stakes next time you see these container grown trees in the nursery).  As trees increase in size and their initial upright form has been established less work is required although not entirely eliminated. 

Poor root system development is another issue we are constantly dealing with in nursery container grown mesquites.  In the wholesale nursery growing environment mesquites grow very rapidly.  The trees are initially grown in small containers and are upsized or repotted to larger containers as they grow and develop.  With such rapid growth it is not uncommon for root problems to develop in terms of girdling roots and/or root-bound plants.  Trees with root problems may be upsized several times with the potential of the same problems reoccurring.  Although root development may be quick, top growth is generally faster.  Therefore, it is possible to not only have a tree with poor root structure, but one in  which the top growth far exceeds and is out of  proportion with the size of the root system.  Even  a nursery container tree with good root structure that is also in proportion with the tree’s top growth, when placed into a landscape environment where it receives frequent irrigation, fertilizer, etc. may once again experience top growth exceeding root development.  This is the reason we often see trees tied to support stakes for several years following installation. 

Loss of newly installed mesquites to winter desiccation is another problem common to Southern Nevada.  Most nursery trees are produced in Southern California and Arizona where winter temperatures are mild.  Planting of these trees in Las Vegas mostly occur during spring and summer months.  With warm weather, irrigation and fertilization trees grow rapidly producing soft tissue.  As often occurs with new landscape installations heavy irrigation continues into the fall and early winter and trees do not have an opportunity to harden off prior to the onset of cold and often freezing temperatures.  With lush growth, soft tissue and wind combined with cold temperatures desiccation and death may occur. 

Rules of Thumb (Green Thumb):

ü      The smaller the better!  Small containerized nursery trees are less likely to have root problems and will often out perform larger containerized trees.  Unfortunately, small container sizes such as 5 gallon are generally not available since the trees will quickly grow to 15 gallon or larger and thus have a greater cash value to the wholesale grower.  Always inspect the tree’s root system prior to planting.  Root pruning may be necessary to correct problems or deficiencies.

ü      Strong, healthy, upright, and attractive mesquites don’t just happen by luck!  Trees will also require considerable training following installation.  Put as much emphasis on developing a strong root system as you do on developing the above ground structure.  This may require heavy pruning of the top growth to keep it proportional to the developing root system.

ü      Don’t over fertilize.  In most cases mesquites require very little fertilizer.  Too much fertilizer will often increase top growth at a faster rate than root growth producing a top heavy tree.

ü      Irrigation system design needs to meet the newly installed tree’s requirements as well as the tree’s long term requirements.  Improperly designed irrigation systems can restrict as well as create rooting problems which may lead to eventual tree failure. 

ü      Keep installation of trees in turfgrass areas to a minimum.  Turfgrass irrigation and fertilization encourages shallow rooting and excessive top growth.

ü      Heavy pruning should only be done during the coldest time of the year.  Trees produce heavy sap flow during warm temperatures.  Large pruning cuts made during warm weather may produce sap flow to the exterior of the tree for months or in some cases years. 

ü      Don’t fertilize newly installed trees and reduce irrigation in the fall to harden off trees for winter.