Ornamentals vary in their requirement, and many such as azaleas require an acid soil, which occur rarely in Arizona. Nitrogen deficiencies are determined by observing tree growth as described above, and through cultural history of the tree, such as how frequently the tree has been fertilized in the past. If fertilization is necessary, follow amount recommendations given with the soil test results. If turf grass or ground covers are growing around the tree to be fertilized, split any application so that no more than one pound of actual nitrogen per 1000 square feet is applied at any one time. This will prevent fertilizer burn of the ground cover.
Space applications six weeks apart.
Apply fertilizer at the correct time of year for best results and minimum potential for groundwater contamination. Fertilizer can be applied in the fall approximately one month after the first frost. At this time, roots are still growing and will benefit from the nutrients, but tender top growth will not be stimulated. The loss of nutrients from winter fertilization is not only expensive, it can result in water pollution. Surface or broadcast application is the most desirable method of application.