Arizona ash trees (Fraxinus velutina) are quite common to Arizona, and are well adapted to the sunny climate here. In fact, many other types of ash trees grow in Arizona as well. There are over 65 species of ash trees. Wikipedia lists many ash trees according to regions where they are found. Be aware that there are other woody plants that have “ash” in their name (such as mountain ash and prickly ash), but are not of the genus Fraxinus, and so are not ash varieties at all. Below is a list of some of the Arizona ash tree varieties, which is by no means comprehensive:

Green ash (Fraxinus pennsylvanica) – also called ‘swamp ash’ or ‘water ash’
Raywood ash (Fraxinus oxycarpa)
Shamel ash, (Fraxinus uhdei) – also called ‘tropical ash’
Fantex ash, (Fraxinus velutina) – also called the ‘Rio Grande ash’
Littleleaf ash (Fraxinus greggii)
Arizona ash (Fraxinus velutina) – known commonly as ‘velvet ash’ or ‘modesto ash’
Singleleaf ash (Fraxinus anomala)
Goodding ash (Fraxinus gooddingii)
Fragrant ash (Fraxinus cuspidata)
Chihuahua ash (Fraxinus papillosa)

The Arizona ash tree has many positive features, but along with those come some drawbacks. Horticulturist Calvin R. Finch, Ph.D., has labeled the Arizona ash a ‘trash tree’ because of its life span of only about 25-30 years, among other reasons.

Ash trees are deciduous, which means they shed their leaves at the end of the growing season. Many types of trees are considered messy, and the ash tree is no exception. Most ash trees, fortunately, limit their leaf drop to a two-week period. Most ash trees also produce seedlings, either all year round or only once per year but in great numbers depending on their gender and species. With an ash tree, you must learn to enjoy raking at least once in a while if you prefer a tidy yard.

The majority of ash species are fast growing trees. While rapid growth makes for quick shade, it also presents drawbacks. Fast growing trees tend to develop surface roots. Although the roots of ash trees often grow close to the surface, they are usually tolerant of a both alkaline and rocky soils However, as described by Watson and Gilman in their Fact Sheet about the green ash tree, these surface roots can “become a nuisance as they lift curbs, sidewalks and make mowing difficult.” Finch is quick to point out another downside to the rapid growth typical of most ash trees: “unless you prune it on a regular basis it can become a tangled mess with frequent branch dieback.” Plan to trim ash trees at least every few years to promote a healthy branch structure and keep its canopy from becoming too dense. Otherwise, there can be weak growth that is prone to breaking. It is not a good idea to allow multiple trunks, as this will eventually lead to structural failure. It is best to establish one central trunk while the tree is still young. Before planting a new ash tree, be sure your yard is big enough. Ash are large trees. While most mature ash trees reach about 40 to 50 feet in height, some can be over 80 feet tall, and all tend to have a full, round canopy.

Arizona ash trees, like many other plants, are susceptible to various pests and diseases. These include cankering, mildews and various fungal infections, leaf scorch, rust diseases, and pests such as mites, webworms, carpenter worms, and borers. Ash trees are particularly vulnerable to Verticillium wilt, which is a soil-borne fungus. In some parts of the country (primarily the midwest), the emerald ash borer has killed many tens of thousands of ash trees. Luckily, Arizona ash tree varieties have not yet been affected by the destructive emerald ash borer (read more about this pest at http://www.emeraldashborer.info). Trees that endure poor environmental conditions are more vulnerable to these problems, so it is important to keep the tree’s defenses up by watering and fertilizing adequately.

In your effort to maintain your Arizona ash tree, I encourage researching according to its species, because there is a surprising array of unique qualities attributed to each. There is a series of several hundred tree fact sheets for species of trees and shrubs, written by Edward F. Gilman and Dennis G. Watson, both professors at the University of Florida. These are a good source of basic information about the specific trees you may wish to learn more about. They are provided in part by the Forest Service and U.S. Department of Agriculture.

If they are maintained well, ash trees are very lush and beautiful. On the other hand, ash trees that are uncared for easily become an eyesore and much more likely to be host to various pests and tree diseases. While certain varieties of ash are fairly drought resistant, most require plenty of water. Flood irrigation will provide the best setting for an ash tree. If your yard is not irrigated, it is best to mimic flood irrigation with the garden hose by deep-watering once or twice per month. If you live in Arizona and have an ash tree in your yard that you hope to keep healthy and looking nice, be prepared to cringe when you look at the monthly water bill. You may also want to fertilize your ash trees regularly. Putting mulch down around the tree is also beneficial for two reasons: it will not only enrich the soil as the organic matter breaks down, but the mulch will also retain moisture from the watering to keep the soil wet longer.

Though they are not especially easy to take care of, it is worth the effort to keep each ash tree in your yard healthy. In return for your service, they will provide plenty of lovely shade. A healthy Arizona ash tree will most certainly enhance the beauty of your yard.