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.