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. To adequately cover the subject of pruning would take more than our typical one page.
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 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. 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. Regular pruning of mature trees can simplify Pedestrian access, improve seating and better accommodate play areas.
Growth management is the least exploited strategy to avoid pruning. Many established desert natives can be naturalized to where they can 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, growth and pruning can still be reduced by limiting irrigation and nitrogen.
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.
Periodic thinning is the most desirable method of pruning. Thinning trees before monsoon season can reduce wind damage to branches and uprooting of trees. Removal of large portions of the tree canopy (more than 30%) during the summer can lead to sunburn injuries that can later be colonized by wood boring insects. 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 10% solution of bleach. 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 at least the first of June. Remember pruning can reduce spring flowering.
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