Weekly Express-News Article

By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist

Saturday, May 31, 2008

“Why Not Pecans?”

            There are shade trees that everyone seems to agree are premium selections in terms of landscape value.  Live oak, Texas red oak, cedar elm, Mexican sycamore, bur oak, and chinkapin oak. They are attractive, live a long time, and prosper in our soil and climate situation.  Pecans and Chinaberries are not on that list. 

 

            A question that often arises when I provide my list of desired shade tree species is, “why aren’t pecans on the list?”  The questioner goes on to say that pecans are beautiful, large, grow quickly, and provide nuts! 

 

            It is true that pecans have some desirable characteristics and are a great choice for some shade tree situations.  They also have some characteristics, however, that make it important that there is some thought invested in making the decision to use pecans as a shade tree in San Antonio. 

 

            Pecans are very large.  On good soil they grow to 70 feet tall and 60 feet wide.  In terms of a typical modern lot, that may be too large.  Planting a pecan is some neighborhoods as a lawn tree is a misnomer, planting a pecan is a neighborhood tree.  The leaves shade several yards and the leaves drop over several lawns. 

 

            Leaves are one thing to consider, but there are even more disturbing things that fall from pecans.  Some trees are prone to drop branches.  The phenomenon is common enough that it is a major consideration. A large pecan tree loaded with nuts is especially vulnerable to breakage when the wind blows. 

 

            Aphid honeydew is not as dangerous as broken branches, but it can be quite unpleasant.  Aphids attack pecan trees and the honeydew is their excrement.  It is sticky and sweet and can cover a lawn, driveway, car, swing set, or front stoop.  Honeydew also provides a great medium for the growth of sooty mold.  Everything becomes black and sticky. 

 

            There is one variety of pecan, Pawnee, that does seem to have resistance to aphids.  It also makes a relatively small attractive lawn tree that produces its thin shell nuts early (September) in the season. 

 

            The question of nuts is not as simple as it sounds.  Nuts are not automatic. To achieve full production, a pecan tree is irrigated at the rate of one inch per week all summer.  Pecans grow best in deep alluvial soils such as river bottoms.  Our characteristic shallow, rocky, or clay soils make the water issue even more important.  In addition to the water, full pecan production requires fertilization and pesticide sprays. 

 

            Nitrogen and zinc are the most important nutrients.  The only practical way to apply zinc is through a series of springtime foliar sprays.  Pecans love zinc, but it kills many other plants, so is not an option in most neighborhoods. 

 

            Pesticide sprays that cover a 70 feet tall tree every few weeks are also not popular or practical in most neighborhoods. 

 

            The only option on watering and spraying that appears practical is to subject your nut production to the whims of nature.  Every few years there is enough rain and/or reduced insect and disease pressure that a quantity of high quality nuts will be produced.  Most years the trees will produce pecans that are empty, shriveled, or diseased.

 

            This lassez-faire management method may not produce a large number of high quality pecans for human use, but even under this regime, the squirrels and other wildlife benefit from a pecan tree. 

 

            Chinaberries are also called umbrella trees because of the shape of their crown.  They are attractive to many homeowners, but rarely are recommended by horticulturists.

 

            The problems with Chinaberries include its huge production of berries, sensitivity, to cold and tendency to spread everywhere.  Chinaberry fruit is not a favorite wildlife food which is too bad because a tree produces a huge amount of it.  Instead of ending up as food for songbirds, the berries end up on driveways and in swimming pools and as a seed source for more Chinaberries.  If there is a Chinaberry in your neighborhood, you can expect seedlings to show up in great numbers.

 

            Chinaberry grows very fast so if you are not vigilant with seedling control you have 10 foot sprouts in one year.  If you let them grow to large trees the soft wood is very susceptible to cold damage.  It can be an expensive problem to cut down a large soft wooded tree.