Because there are so many different types of trees from which to choose, you can select varieties specifically suited to your needs.

First you must identify exactly what function you want your tree to serve. Trees may be used for shade, ornament, screening, windbreaks, to reduce noise, to shelter wildlife and to provide edible fruit or nuts.

The intended purpose will influence your selection criteria of shape, size, type of foliage, and other physical characteristics.

Providing shade usually requires tall, sturdy, long-living species. Density of foliage and shape determines the amount of shading a tree will provide. Some trees produce a very dense shade that prevents other plants from growing under it, while others provide a light filtered shade that does not hinder plants growing beneath. Tall trees with long, spreading, or weeping branches give abundant shade. Deciduous trees should be used to shade southern-facing windows in summer, since they will allow the sun to penetrate in winter.

Screens usually require plants that produce a dense foliage, such as evergreens. In addition, windbreaks and other barriers require sturdy plants with a dense growth, and possibly thorns or spines.

Ornamental attributes are quite varied. Both trees and shrubs can be selected for flowers or colorful fruit, interesting foliage, fall color, interesting bark, winter colors of foliage or branches, or interesting shapes of the plants themselves.

In selecting fruit and nut producing trees it is important to evaluate the tree's chilling requirements for fruit set and the chilling hours typical of your area. The tree's requirements will be identified on the tag at the nursery. Check with your local Cooperative Extension to identify the number of chilling hours (continuous hours below 45° F) typical of your area.

To provide wildlife habitat select trees that produce food and or shelter. Fruits, nuts, and berries all attract animals. Trees with dense foliage and thorns provide safe nesting spots.

Consider the growth habit of the tree. Evaluate the size of the tree when mature and where it is to be used. Tall-growing trees, such as the eldarica pine, and Chinese pistache are suitable for two-story and larger buildings. They tend to dominate the low flat appearance of -- or even hide -- one-story buildings. For attractive and proper balance with one-story buildings, trees that do not grow over about 35 feet are recommended. Trees can rarely be kept small by pruning, and to do so requires intensive maintenance. Careful consideration of mature sizes will reduce the need for pruning.

Once you have determined exactly what you want in a plant, you must evaluate what you have to offer it. Site characteristics that should be reviewed include the space available, the environment, soil conditions, and potential pests. Consider both the size and the shape of the available space and how that will change as the tree matures. Environmental characteristics include extreme heat or cold, drought or flooding, reflective sun and shade, exposure to wind and pollution. Soil pH, drainage, and depth are all factors to consider when selecting a plant. Most trees will require a minimum of 18-24" of well drained soil. Soils with high salinity, low fertility, or toxic pollutants will limit tree selection. Potential pests include insects, diseases, mammals (deer, rabbits) and related organisms. In some cases the likelihood of fire may be a consideration. Highly resinous trees, such as pines, tend to burn hotter and longer. Use the information about your site to select a species or variety that is well suited to the challenges to which it will be subjected.

Consider how much maintenance the plant will require and any possible disadvantages including soft or brittle wood that is easily damaged by wind and ice; fruits and seeds that are large, messy, smelly, or otherwise obnoxious; abundant shedding of twigs and small branches, allergenic or poisonous parts, thorns, weediness, water requirements, growth rate, longevity, etc.

Finally, strive for diversity. Do not plant the same variety of trees as your neighbors.

Trees and shrubs immune to root rot

These trees can be planted without special treatment.

Trees: True Bamboos, Banana, Ornamental Palms, all species

Shrubs: Agaves, Bird of Paradise, Dracena, Yuccas, Pampas Grass, Giant Reed

Trees and shrubs resistant to root rot

Recommended for planting in treated soil, or near locations where root rot is known to occur.

Trees: Aleppo Pine, Cedar Elm, Citrus Cypress (Arizona, Italian and Monterey), Eucalyptus, Evergreen, Tamarisk, Fruitless Mulberry, especially Stribling or Sycamore-leaved Mesquite, Palo Verde, Sycamore, American and Arizona Walnut, Native Black Sweet Acacia, Lysiloma, Salt Cedar, Desert Willow, Canyon Hackberry

Shrubs: Cacti, Crepe, Myrtle, Elderberry, Arizona Honeysuckle, Japanese Jasmines, Junipers, Ocotillo, Oleander, Pomegranate, Pyracanthas, Rosemary, Russian Olive, Siberian Pea Shrub, Hop Bush, Creosote Bush

Trees and shrubs very susceptible to root rot

It is not worth planting these in treated holes or near any location where root rot has occurred.

Trees: Bottle Tree, Carob, Cottonwood, Elm Fig, Ginko, Pepper Tree, Poplar, Stone fruits -peach, plum, apricot, almond

Shrubs: Buddleias Cassias, Castor Bean, Cotoneaster, Silverleaf, Lilacs, Photinia, Chinese Quince, flowering Roses, Silverberry, Spirea