For The Answer
Weekly Express-News Article
Saturday, November 5, 2005
By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist “Why They are Called Trash Trees”
Last week we discussed the most desirable shade trees and how to plant them. Fall is the best time to plant shade trees (shrubs and perennials, too!) and your favorite nursery probably has them on sale. There are a number of trees, however, that your nursery probably does not have for sale. They are often described as “trash trees” because they have one or more characteristics that make them undesirable in the landscape.
Hackberries lead the list of “trash trees.” Hackberries are undesirable because they reseed prolifically, do not usually develop an attractive crown, and can be short-lived. The species produce huge qualities of seed at this time of the year. The seed is contained in a berry like capsule that is a favorite food of the birds all winter. The birds consume the berries and then excrete the seed along fence lines, in your rose bushes, and every place else that they roost. The germination rate is very high.
On our typically poor soils the hackberries do not reach a large size and often have a raggedy appearance. They also seem to be susceptible to diebacks and are short-lived on many sites. This is not always the case, however, on deeper soils hackberries reach over 50 feet tall and if they have room to develop and receive full sun, they can form a handsome tree. For the wildlife value hackberries are important, but they are not the best shade tree for most landscapes.
Mulberries are also usually described as a “trash tree.” They grow very fast and reseed nearly as aggressively as hackberries. Mulberries are one of those tree species that will drop their leaves early during droughty summers. With conscientious pruning they can be shaped to form an open crowned shade tree, but they grow so fast that most people do not prune them adequately and they become quite tangled. Mulberries are almost as good as hackberries as a wildlife food source. In my neighborhood the edible berries are all stripped from the trees before they even ripen in the spring. Cardinals, doves, grackles, starlings, mockingbirds, buntings, wrens, and even warblers feed on the berries.
Chinese tallow is short-lived and spreads far and wide like the other “trash trees.” It has an autumn berry that is white and decorative. The birds eat the berries, but not with the same relish as mulberries or hackberries. Foliage color is the tallow’s claim to fame. It is an attractive light green in the spring and can have red purple foliage in the autumn. The trees are sensitive to cold and brittle in the wind. The Chinese tallow leaves resemble pear leaves in shape and blow in the wind like aspen leaves.
Chinaberry has a purple bloom every spring and is a bountiful berry producer in late summer. The berries are as large as grapes and produced in clusters. Birds eat a few and spread enough that the seedlings are a nuisance, but it is not a favorite bird tree. The result is that the berries are messy. Pool owners find Chinaberry as especially pesky. The crown has a pleasing shape. Chinaberry is sometimes called umbrella tree. Chinaberry is sensitive to cold and relatively sensitive to drought so trees in the San Antonio area are usually short-lived.
One tree that many landscapers designate as a “trash tree,” but is for sale in most nurseries is the Arizona Ash. The tree grows very fast and unless you prune it on a regular basis it can become a tangled mess with frequent branch dieback. Arizona ash is attacked every spring by anthracnose (a foliage disease) and is a favorite food source for insects. The seeds are formed in large numbers in the spring (a similar, but less common ash has seeds in the fall). The seeds are eaten by birds with the result that Arizona ash spreads around the neighborhood. A well cared for Arizona ash often only lives for 25 – 30 years before anthracnose and other stresses end its life. At that time it can be quite large and expensive to cut down.
In most cases it is best not to select the trees described in this article for your shade tree. For a long-lived high value shade tree select from among live oak, Texas red oak, Mexican white oak, Montezuma Cypress, cedar elm, bur oak, chinkapin oak, Lacey oak or Chinese pistache.
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