The Texas Forest Service has an interactive guide for tree selection. Input conditions (sunlight, soil conditions, height, etc.) and get a list of suitable trees. They also have a Tree Planting and Care Guide to help you select a site, plant and maintain your trees.
Denton County Extension Agent Emeritus, John Cooper, has taken the mystery out of tree planting. His article, Tree Planting and Care, explains how to prepare the soil, which tree to select, and how to plant and irrigate young trees.
What’s Wrong With My Tree?
Most tree problems seen by Master Gardeners are not diseases but abiotic factors, meaning improper planting, watering, weather damage, etc. When trying to diagnose a tree problem, first consider the age of the tree. If it has been planted within the past two or three years, it may be that the tree has not overcome transplant shock. The tree will look thin, and the top may not have leaves at all. Another very common problem is underwatering. A new tree needs infrequent but deep watering. In the absence of rain, water the tree once a week. Give it at least 1 to 1-1/2″ of water; the ideal is to use a soaker hose. The regular irrigation system may not provide enough for a new tree. Conduct a water audit to find out. A very simple way to audit the sprinkler system is to put out tuna cans (or similar size) and run the system for 30 minutes. Measure the water in the can to figure out how long to run the system to get one to 1 1/2 inches each time you water.
If there is a disease process, fungal diseases are the most common. The Texas Plant Disease Diagnostic Lab will diagnose diseases for a fee. Look at their Plant Disease Handbook for a description of common diseases.
For professional help, consider hiring a certified arborist to diagnose and possibly treat the tree. The International Society of Arboriculture “Find a Tree Care Service/Verify an ISA Certification” page can help you find an arborist based on your zip code.
One of the most common native trees in Denton County is the post oak. These lovely natives do not transplant well, so if you are lucky enough to have them in your landscape, take good care of them. John Cooper, Denton County Extension Agent Emeritus, wrote an extremely helpful article called, “The Care and Feeding of Post Oaks.” It is well worth reading. He also wrote “Care and Feeding of Pines in Denton County.”
Homeowners are concerned about oak wilt due to heavy media coverage about the condition. Denton County has had very little trouble with oak wilt to date. Chances are good that is not what is bothering your oak tree. However, read the symptoms here.
If you know what type of tree you have, the IPM Online site from the University of California Davis can help you find out what diseases may be afflicting it.
This is a good article about oak tree diseases.
When storms come, limbs or sometimes entire trees are damaged. Check the AgriLife Extension Tree Care Kit for tree first aid.
For varieties recommended in North Texas, check these lists: Fruit Trees for North Texas
If you think it is not possible to grow citrus trees in Denton, think again. This article by a Denton County Master Gardener will help you get started: Growing Citrus in North Texas
Successfully growing peaches in Denton is a daunting task, but many try. Here is the definitive guide to insect control on peaches, apricots, nectarines and plums.
For landscape shade trees, pruning is only necessary to remove dead limbs. Should you choose to prune for other reasons, remember that the tree does not require it. Trees need leaves, so be cautious before pruning. In particular, do not top a tree unless you want to permanently stunt its growth. The most common victim is crape myrtle (it is sometimes called crape murder). There are legitimate reasons for pruning, such as aesthetics or to be able to mow underneath a tree. Reducing shade so that grass will grow is not the best option for the tree, although you might decide it is the best option for you. If it is too shady for grass, then planting a shade-tolerant ground cover is preferable to lifting the canopy year after year.
Pruning is part art, part science and usually completely confusing for homeowners. There are some tricks to doing it properly. Go to these links for more discussion:
Before fertilizing trees, lawn, or any other plant, find out what the soil needs. You can download forms and instructions for a soil analysis. To give the soil what it needs, at the right time, and prevent runoff, follow these instructions. Most of the time, trees do not need supplemental fertilization. If you fertilize your lawn, that may be plenty for the trees as well. Do NOT fertilize a sick tree. Get the problem properly diagnosed before performing any type of treatment, including fertilizer.