For The Answer
By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist
Week of November 7, 2005
“Plant Shade Trees Now”
Now is the best time of the year to plant shade trees, shrubs and most perennials. The plants have plenty of time to develop a root system before they must face the stress of a San Antonio summer, the weather is pleasant for us to be working in the yard to plant the tree or shrub, and most nurseries have plant sales that make it wise to buy now.
My colleagues on the Gardening South Texas radio show – Milton Glueck and Jerry Parsons say the best way to determine how large the tree you buy should be is to dig the hole first and then buy the tree with a root ball to match the hole. This unusual recommendation makes sense because in many parts of our city, the soil is rocky and a hole is hard to dig. The recommendation makes sense because it saves were and tear on the hole digger.
The recommendation also makes sense because in soil like ours, a smaller tree will more easily become established and begin growing. A larger specimen is at risk for the long period it takes for the root system to develop enough to support the overly large crown. In many cases a smaller tree planted at the same time as a larger specimen will catch up and surpass the larger tree in a few years. Make the choice to plant a smaller specimen at the first and save wear and tear on you and on your pocket book. Larger specimens are much more expensive than the smaller trees at the nursery. 10 feet tall to 2-inch diameter tree is often the best investment.
Some of our soils are difficult to dig so select a tree from the nursery that is relatively small so you can manage digging the hole without the need for dynamite or heavy equipment. Dig the hole only as deep as the root ball and two or three times as wide. Never plant the tree too deep. It is best to have it stick out of the ground rather than have it in a sunken area. Do not waste your time or money adding additives (compost, planting fertilizer, or micronutrients) to the hole. As far as I know there is no research that verifies that the expensive additives contribute to survival or growth rate. What does help is to mulch over the root system three – four inches deep to keep the soil cool, reduce evaporation, and keep weeds and grass from competing with the tree. Shredded brush, leaves, or partially finished compost make good mulch. Do not put the mulch against the trunk.
Tamp the soil in place with your foot and run the hose at a low rate until the hole fills with water. The soaking will help eliminate large air large air pockets that contribute to root death.
Texas is no set schedule to watering after the original soaking. Feel under the mulch once/week for the first year and add enough water to cover all the roots (5 – 10 gallons) when the soil is dry to one inch. That usually means you may only water once/month the first winter and spring and then once/week over the first summer. By next autumn the tree should be established enough to prosper without irrigation except in droughty summers. Water once per month when it is dry in the summer after the first year.
The best shade trees for San Antonio are live oak, Texas red oak, Mexican white oak, Montezuma cypress, cedar elm, bur oak, chinkapin oak, Lacey oak, and Chinese pistache.
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