Correct and timely pruning can enhance the beauty, health and durability of arid landscapes. Poor pruning can ruin landscape trees. Successful pruning requires an understanding of the growth habits and unique horticulture of the tree being pruned. Most popular desert landscaping books dedicate at least one section to pruning. These books are excellent references that cover subjects like crossing branches, proper cutting techniques and tools. They also provide helpful diagrams and detailed descriptions. 

Our purpose here is to introduce some general concepts and considerations. It bears repeating, pruning can do as much harm as good. If you are not sure what to do, get a certified arborist's professional advice. Fortunately, extensive pruning is not required for most desert tree species when they are carefully located in arid landscape designs. Proper tree placement and growth management can significantly reduce the amount of pruning desert adapted trees require. When placing trees in the landscape consider the mature height and spread of the tree. If in doubt, mildly exaggerate the mature size rather than underestimate. Plant trees strategically around structures, play areas, pedestrian traffic and other trees so that mature trees can provide maximum shade with minimal interference. Also consider how mature trees will interact with other components and uses of the landscape. 

Typically most desert adapted trees with small leaves and light colored trunk allow filtered light through the canopy while species with dark trunks develop heavier shade. When under story plantings are located beneath dense canopy trees (like mesquites), regular thinning of the trees will be needed to admit adequate sunlight for flowering and lush growth. Annually evaluating pruning of mature trees can reduce potential storm damage, simplify pedestrian access, improve seating and better accommodate play areas. 

GROWTH MANAGEMENT: Growth management is the least exploited strategy to avoid pruning. Many established desert natives can be naturalized to where they survive with little or no supplemental irrigation. The practice of limiting water and fertilizer serves to significantly slow growth and reduce the need for pruning and thinning. For species that cannot be naturalized, limiting irrigation and nitrogen can still help reduce growth and the need for pruning. 

Periodic light thinning is the most desirable method of pruning. Such light thinning is especially important in June, July and August. This pruning can reduce the number of wind damaged branches and prevent uprooting of trees. Removal of large portions of the tree canopy (more than 30%) during any one pruning session in the summer growing season, can lead to aggressive, unwanted re-growth, limited root development and increased vulnerability to sunburn injuries that can be colonized by wood boring insects. No more than 20% of the tree foliage should be removed at any one time with 80% of this pruning concentrated on the new growth on the outer third of the canopy. The remaining 20% should be removed from the two thirds of the canopy removing succulent ("water") growth and crossing branches.

Avoid hedging or heading back desert species, as this will only stimulate excessive branching. Always use clean, sharp tools that are regularly cleaned in a fresh 10% solution of bleach. Bleach act as a sterilizing agent and help prevent the spread of diseases within and between trees being pruned. Some desert species are slow to exhibit the effects of freeze damage. Branches that do not immediately bear leaves in spring may not be damaged. Delay pruning suspect branches until the tree has begun producing new leaves. Realize that early season pruning can reduce spring flowering.

NATURAL FORM: It is all together too common for the natural growth characteristics of arid region trees to be completely ignored when these species are pruned. Trees native to mixed conifer and hardwood forests have a generally upright growth habit, typically dominated by a strong central leader. In these forests competition is primarily for light. The ability to grow straight and tall give those trees a significant competitive advantage over trees with other growth habits. In the southwestern desert competition is primarily for water. In this habitat trees are highly dispersed and individual species tend to grow nearly as wide as they are tall producing branches that extend to the ground. This unique growth habit must be considered when developing pruning practices for desert region trees. The goals of pruning desert trees must be to promote tree vigor and health, and to enhance and compliment the natural form of these native species. 

In the process of developing proper structure, caliper and branch and trunk taper nurseries encourage the growth of "temporary branches." These branches, usually removed when they are around one quarter to half inch in diameter, promote the development of caliper and branch thickening but are not a part of tree's mature trees. If the process of shaping and structure development, begun in the nursery, is to continue once the tree is installed in the landscape, care is required in selecting the correct limbs to prune during the growing season, and determining the appropriate amount of wood to remove. Such pruning promotes proper growth of both feeder and stabilizing roots, keeps leaf and root mass in balance, and forms well defined branching structure.

Beyond this point, all that is required is maintenance pruning and thinning to compliment and reinforce the established form and remove potentially problematic branches. It follows then that, in locations where single leader, upright trees are required, the desired ultimate form will need to be established at the time trees are purchased and installed. To develop adequate taper and caliper, for single trunk trees to support the canopy, requires keeping lower temporary limbs on the tree perhaps for the first few growing seasons. This time frame depends on the tree size when planted and the rate of growth following installation. Rushing to raise the canopy height on single trunk trees by remove temporary or major limbs to soon will often encourage S or C shaped trunks. 

Attempting to substantially modify the structure of desert species (e.g. pruning a low branching multiple trunk tree into a more single trunk form) is almost never successful. The typical result is trunks that have a corkscrew or highly twisted, unbalanced shape with large gaps between branches and numerous, large and unsightly pruning scars. 

PRUNING PHILOSOPHY: It is ALWAYS preferable to regularly remove many small branches than to periodically remove a few larger ones. Removal of crossing and parallel branches and branches that pose hazards to foot traffic should be removed first. Both crossing and obstructing branches are best removed when they are relatively small twigs. By starting with "clean-up pruning" (the removal of small branches), the general form of the tree is more apparent. Stop periodically and step back from the tree, like an artist working on a painting, and take in an overall view of the tree from ALL sides. Identify problem areas, look for balance then begin pruning again. Repeat this process several times while pruning. Recall that improper or inappropriate pruning can act to stimulate additional unwanted growth. Corrective pruning can stimulate desired growth or reduce and better control growth and form. 

The most common point where tree branches fail is at the junction of two or more co-dominant or adjacent branches. This failure usually is from an included bark branching juncture or from lion tailing the trees branching structure, over burdening the branching connection points. Included bark is bark embedded or a bark ridge turning inward between opposing branches, a branch and a main trunk or two co-dominant branches creating a structurally weak point in the tree Included bark prevents strong attachments of branches, often causing a crack at the point where branches meet. An inward bark ridge line usually develops where they join and, more importantly, the included area declines or dies from to the cambium of both branches being squeezed and killed, weakening the branch or trunk. Trees with co-dominant leaders tend to have included bark and are more likely to split and ultimately fail. Included bark may be remedied by removing the smaller of the two branches or the one supporting less of the overall mass. Branches with wider or U-shaped angle of attachment should be retained. Good branch attachments have a raised ridge line or collar at the point where branches meet.

 PRUNING METHODS: It is well documented that sharper pruning tools make cleaner cut that generally heal rapidly. Keep pruners and saws sharpened clean. Use the appropriate tool for the size of branch being removed. "Fine toothed" saws can be used on larger branches to finish a pruning process, leaving a smooth cut surface that will quickly heal. Removal of small branches can be done almost any time of year. Fall and winter have the advantage of giving the individual a better view of the structure of branches when leaves are being shed. Clearly the objectives of any pruning program must be to foster tree health and vigor in concert with the natural form and character and to compliment the landscape design. 

Pruning can have a number of effects on trees. It can compensate for root loss, aid in maintaining health and appearance, control plant size, influence vigor and re-invigorate stagnant trees. Two things should always be appreciated when pruning: 1) improper pruning can serve to stimulate additional unwanted growth; and 2) each pruning cut creates a wound in the tree bark. Proper and selective cuts will enhance the appearance and health of trees and leave wounds that will heal rapidly. The angle and position of pruning cuts greatly influences the overall success of a pruning program and dictate how quickly wounds will "heal". Pruning cuts should be made close to, but not beyond, the branch bark ridge and the collar at the base of the branch (see diagrams). 

Sharp tools that make clean, smooth edged wounds will heal the quickest. These wounds don't "heal" like animal wounds. Instead trees produce callus tissue that essentially "re-covers" the injured area. Wounds heal from the edges as seen with the ring of raised or swollen bark surrounding the edges of the wound. The bark tissue forms a callus, giving the edges of the cut this raised appearance. Over time, with growth and the subsequent increase in the branch diameter, the old wound is closed completely. A dull pruner and saws leave ragged edged cuts. Such cuts develop callus more slowly delaying the healing process. Wounds that are slow to heal can be sources of oozing sap (that can stain hardscape elements and patio furniture) and serve as points of entry for insects, bacteria and fungi. These pests can cause additional damage and further delay healing. 

Another common mistake is leaving short stumps instead of pruning branches off just above the collar. Aside from being extremely unsightly (and unprofessional looking) these stubs can sunburn, dry out, cause die back and serve as entry sites for some wood boring insects, bacteria and fungi. Tree borer damage is often misidentified as being caused by tree stress or general decline when in fact it is the result of stub pruning. Secondly stubs can snag clothing or the skin of pedestrians. Most importantly, such cuts generate additional unwanted branches by stimulating both lateral and adventitious buds (bud arising from previously woody tissue) to produce numerous new branches. This proliferation of branches must ultimately be removed by additional pruning. 

Removing the branch at the collar serves to direct the subsequent growth towards the terminal of the remaining branch without excessively stimulating other buds to produce additional branches. Similarly, when heading back a branch, pruning back to a lateral bud seems to direct the branch growth through that bud making it the new terminal bud (see diagrams).