For The Answer
PRIMETIME NEWSPAPERS WEEKLY COLUMN
Week of May 14, 2001
By Calvin Finch, Conservation Director, San Antonio Water System, and Horticulturist
CARE OF NEWLY PLANTED TREES
Shade trees are important for several reasons. A San Antonio summer would be unbearable if we couldnt escape to the shade of oaks or other large trees. The trees reduce water use on landscapes and save huge amounts of energy in the form of air conditioning. Trees are attractive and add thousands of dollars to our property values. Trees also can be important for birds and other wildlife.
The best time to plant trees is in the autumn but, with good container-grown stock, any time is a suitable time for tree planting. If you plant trees now you just have to be more careful about mulch and watering. Three to four inches of shredded brush, bark, leaves, pecan shells or compost is essential to protect the roots and maximize the growth rate. Research shows that most newly planted trees grow 40 percent faster with mulch over the roots compared to grass growing up to the trunk. The mulch also makes it unnecessary to use the string mower around the tree trunk. I would guess that more trees die from string mower girdling in South Texas landscapes than from drought.
When you apply the mulch, put it on in the form of a donut shape. The hole in the middle keeps the trunk in contact with the air. A newly planted, mulched tree may grow 40 percent faster than one where lawn grass is allowed to grow up to the trunk.
Water the newly planted tree generously when it is planted so all the large air pockets are eliminated and soil is damp enough to encourage root growth. To determine when to water again feel under the mulch and water when the soil is dry. This will probably be every week to two weeks in the summer. Add enough water to fill the planting hole (usually 5 to 10 gallons) at each watering.
Even with the threat of oak wilt, live oaks and Texas red oaks are the best choice for shade trees in the San Antonio area. Other good choices are chinkapin oak, bur oak, Chinese pistache, cedar elm, Mexican white oak and Montezuma cypress.
Pecans, Chinese tallow, cottonwood, sycamore, Arizona ash, hackberry, magnolia, mulberry and Chinaberry work in some situations but are generally less desirable due to problems with disease, short life and/or breakage.
Full size shade trees need plenty of room in full sun to prosper. If you do not have an area about 50 feet around for a full size shade tree consider the smaller trees such as ornamental pear, desert willow, redbud, loquat, standard yaupon or crepe myrtle.
A full size shade tree should always be planted at least 20 feet from the house, 30 feet is best. Dig a hole as deep as the container and two to three times as wide. It is not necessary to add root stimulator or organic material to the hole. The tree has to survive in native soil eventually and, in some cases, the addition of sand or organic material to the hole contributes to root drowning. Right after planting, the roots are limited to the planting hole. If water can enter the hole more easily than it leaves, it stays soggy in high rainfall periods, killing the tree.
Of the full size shade trees listed as desirable, Texas red oak, Montezuma cypress and Chinese pistache will grow fastest on most sites. The others would probably be described as moderate growers.
Oak wilt is a threat to live and red oaks in the San Antonio area but it is easy to prevent. If your neighborhood is dominated by live oaks or red oaks, it may be best to select one of the other recommended species (Mexican white oak is evergreen like the live oak and does not seem to be susceptible to oak wilt). Even in such environments, if you and your neighbors paint all wounds on susceptible oaks and stay alert for oak wilt symptoms, you can protect your trees. For oak wilt information call the Texas Agricultural Extension Service at 467-6575, the Texas Forest Service at 208-9306, or visit the web site www.plantanswers.com
There is always the question of what size tree to purchase and plant. Big trees may provide instant shade but they are expensive and require that large holes be dug. In my experience, a tree with a 1½ to 2½ inch diameter trunk seems to be the best buy. Smaller trees adapt fastest to the transplanting and may actually catch up and pass the size of the bigger transplant within two to three years.