Selecting and Planting Shade Trees

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Goose Island Oak is estimated to be 1,100 years old.
The Goose Island Oak stands near Rockport and is thought to be more than 1,100 years old.

If your landscape needs shade trees, spring is a good time to plant them. Planting trees in winter and early spring gives them time to develop a root system before they must cope with summer temperatures and drought.

Live oaks are the favorite and most valuable trees in Central and South Texas. With sturdy, horizontal branching, live oaks are attractive, and once established they’re drought and pest tolerant. They’re called evergreens but do drop leaves briefly every March.

Live oaks can be infected with oak wilt, which spreads through their interconnected root systems. To minimize the risk of oak wilt, paint all wounds and pruning cuts. If your neighborhood is dominated by live oaks, you may want to pick another variety.

Live oaks grow at a moderate pace and live a long time. While they will survive in poor soils, they grow faster and larger in deep soils.

Mexican white oaks are drought tolerant evergreens in the same sense as live oaks. They grow faster and more upright than live oaks reaching 50 feet. Mexican white oaks aren’t susceptible to oak wilt, so they’re a good choice for areas dominated by live oaks and red oaks.

[pullquote width=”300″ float=”left”]Recommended varieties:
live oak, Mexican white oak, Shumard oak, Texas red oak, cedar elm, bur oak, chinquapin oak and Mexican sycamore[/pullquote]

Cedar elms are deciduous trees, but their leaves are very small. Raking is usually not an issue. Cedar elms grow at about the same rate as live oaks, and their shape is similar to Mexican white oaks, although they may eventually grow to more than 60 feet. Cedar elms are drought tolerant and survive by dropping their leaves early under drought conditions.

Shumard oaks and Texas red oaks are drought and pest tolerant red oak species with similar leaves. Both are long-lived, high quality deciduous oaks that grow faster than live oaks. Shumard oaks are usually selected for planting in acid soils while Texas red oaks are better suited to alkaline soils. Shumard oaks grow to 100 feet tall on well-watered sites with good soil; Texas red oaks are usually half as tall.

If conditions are right, individual red oaks can provide good fall color. They also can get oak wilt, so painting pruning wounds is important.

Bur oaks belong to the white oak family, so they resist wilt. Their large leaves and tennis-ball-sized acorns make bur oaks distinctive. They have an open, sturdy branching structure and will grow to 70 feet in some locations. On most sites, bur oaks begin to grow slowly, but over time the rate increases reaching a maximum growth rate similar to Texas red oaks. Like cedar elms, bur oaks drop their leaves early during drought.

Chinquapin oaks are deciduous white oaks that have a relatively narrow crown shape and sport slender, saw tooth edged leaves about four inches long. Chinquapin oaks are well adapted to limestone soils.

Mexican sycamores have distinctive, large leaves with unique silvery and hairy bottoms that are showcased when the wind blows. They are deciduous, and the large leaves can cover the ground in autumn. In addition to their distinctive leaves, Mexican sycamores have sensuous bark with patterns of gray, silver and brown that enlivens the winter landscape. Mexican sycamores grow fast, about the same rate as Texas red oaks, and reach a height of 60 feet.

If sycamores fit into your landscaping plan, choose Mexican sycamores instead of American sycamores. While the latter grows fast and are decorative, they’re short-lived because of their susceptibility to the disease anthracnose. To differentiate between the varieties, examine the undersides of the leaves; the leaves of American sycamores have a smooth finish while Mexican sycamores’ leaves are hairy underneath.

Planting instructions
To obtain the best results, plant new trees at least 30 feet away from your house and other trees. Planting a shade tree on your home’s south or west side can help reduce cooling bills significantly.

The planting hole should be two to three times as wide as the tree’s root ball and the same depth as the container. The top of the root system should be at the soil surface. Planting trees too deeply can cause the trunk to rot where soil is piled against it.

Backfill the hole with the native soil instead of potting soil or compost. Using native soil reduces the chance that water will enter the hole easily but not drain properly. A newly planted tree can’t tolerate a soggy root area that doesn’t drain.

Place four inches of mulch—leaves, shredded brush or bark chips—over the root system. Use leaves that drop from your deciduous trees or live oaks. If you don’t have enough leaves to provide adequate mulch for the new trees, ask neighbors for those they’ve bagged for the landfill.

Wait to fertilize until the second growing season. Next spring use one cup of slow release lawn fertilizer for every inch of the new tree’s diameter. Spread fertilizer around the tree in the mulch and beyond.

Water new trees generously at planting and then every time the soil under the mulch is dry to the touch, which may be every two weeks during the first year.

For the first four to five years, resist the urge to prune stems bearing foliage. Every leaf on a tree contributes to its growth. Fewer leaves mean a slower growth rate.

Protect the trunk from damage by string trimmers, lawn mowers, deer rubbing and other causes. Gouges or wounds on young bark disrupt the vascular system just under it, which reduces the tree’s growth rate and drought tolerance.

Specimen selection
When selecting a shade tree, one of the most difficult decisions is choosing the appropriate size. Instant shade is desirable, but large trees are expensive and sometimes adjust more slowly to transplantation.

Consider selecting a moderate-sized specimen in a 10 – 15 gallon container. It’s easier to dig a moderate-sized hole than a large one. Often times, smaller trees adjust to transplantation more quickly, meaning they outgrow the larger specimens.

More information
For more information on growth rate, drought tolerance, pest resistance and other characteristics of the recommended shade tree varieties, visit plantanswers.com. While you’re there, explore other articles explaining why I don’t recommend Arizona ash, pecan, cottonwood, Chinaberry and hackberry as shade trees for our region.

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by Calvin Finch, PhD