For The Answer
Week of September 22, 2003
Submitted by Calvin Finch, Ph.D., Conservation Director, San Antonio Water System, and Horticulturist
TREES FOR WILDLIFE
Autumn is the best time to plant shade trees. Dig the hole as deep as the root ball in the container and two or three times as wide. Do not be overly ambitious in selecting the size of the tree, especially if you have soil that is rocky or thin. A tree that is 2 inches in diameter or less more readily gets established in poor soils and will often grow faster than a larger more expensive version of the same species. It is also much easier to plant a small tree than a large tree. Do not bother adding root stimulator, soil activator, or even compost to the planting hole. There is no evidence that the materials improve growth rate or survivability. What does work is mulch applied 3 to 4 inches deep over the root system on the surface of the ground.
The best shade trees for the San Antonio area are Texas Red Oak, Monterrey Oak, Live Oak, Chinese Pistache, Lacey Oak, Cedar Elm, Bur Oak, Chinkapin Oak, and Montezuma Cypress. They can tolerate our soils, climate, and pests to live a long time with minimal problems. Shade trees can also be important food sources for wildlife. The oaks are well known for acorns that provide food for wildlife. Chinese Pistache is less well known but is a great wildlife tree.
The Chinese Pistache is a quality medium-size shade tree for the San Antonio area. The females of the species are also outstanding producers of berries for the birds. The berries are produced in mid summer. You can expect a bearing tree to be alive with many different species of birds.
Do not expect to be impressed with Chinese Pistache in the nursery. They are single-stem sticks that reach for the sky for a few years before they form a crown. Rush the process by pruning back the lead stem. The female trees are the only one with berries; it is not possible to determine sex until they reach 20 or 25 feet tall (4 or 5 years). If you end up with a male tree it will not be as attractive to the wildlife but it will still be a well-formed shade tree with good fall color.
There are some other trees that do not qualify as long-lived high-quality shade trees by most definitions but they are outstanding wildlife trees. Mulberries and hackberries are the best in this category.
When we are talking shade trees for wildlife, we mean the mulberry with fruit, not the fruitless mulberry. White and red mulberries are available sometimes in area nurseries but usually they must be obtained from mail order nurseries as small trees or from friends that have a mother tree. Mulberries readily reseed and are spread far and wide by the birds that eat the berries. In fact, in spring the berries are so popular with cardinals, mockingbirds, doves, finches, starlings, cedar waxwings, and other birds that the berries are usually eaten before they ripen fully.
Mulberries grow very fast, 4 or 5 feet per year and have shallow golden roots that can fill a raised bed garden in a year. Expect them to grow to 40 feet tall and nearly as wide. They are also relatively short lived. Use mulberries in the yard away from the house and flowerbeds for most satisfactory impact. The birds will love you for it.
Hackberries east and north of San Antonio a few hundred miles perform well as a shade tree. In the San Antonio area, however, they are inclined to be brushy short-lived trees that do not have the dignity or character of our beloved oaks. In terms of wildlife food for birds in the fall and winter, they are unmatched, however. The little berries attract all of the same species as the mulberry over a much longer season. Hackberries also are often selected as a nesting site by birds and keep woodpeckers and other insect eaters entertained and fed with their dead branches and many insect pests. If you have the land keep a few hackberries and mulberries hidden in corners of the yard for the birds.