Desert landscape trees exhibit an amazing variety of flowering habits, shapes, sizes and colors. Flower shapes include ball or spherical, elongate, spike-rod, tubular and funnel. Some species may produce flowers intermittently through the year while others flower for one or two seasons. Flowers serve not only to provide seasonal color and fragrance(s) but also attract hummingbirds, other birds (feeding and nesting) and wildlife.

Surprisingly the factors that encourage or suppress flower production in desert tree species are not well documented. We can draw some general inferences from observing these species over a number of years. VIGOR: While there may be exceptions, vigorous, established trees tend to flower more strongly than do stressed or recently transplanted trees. Vigor as a component of flower production is seen in the undisturbed desert where abundant winter rains enhance spring flowering. PRUNING: Heavy pruning, conducted prior to the blooming season(s) for a specie, reduces the total number of flower bud when bud bearing limbs are removed. SUN/EXPOSURE: Trees growing in full sun will flower more profusely than those that are shaded for part of the day by neighboring trees or structures. Shading may act to reduce the growth and quantity of branches bearing blooms. Seasonal Variations: The number of flowers may vary from year to year as a result of a whole host of subtle climatological and environmental conditions that may not be conspicuous but that affect flowering. Each individual tree will maintain its own particular timetable for producing flowers. For example, some species will flower following summer rain storms. Its important to appreciate that spring in the desert southwest can be a fairly ambiguous season. Some years it can begin in February and last through June, in other years it is a 3 to 4 week period of mild temperatures just prior to the onset of 105 degree days. Spring is, by far, the busiest flowering season in the desert southwest particularly among Sonoran desert natives. The four popular Palo Verde species overlap their flowering periods sequentially over the spring months (Sonoran Palo Verde first, then Blue Palo Verde followed by Foothill Palo Verde and Parkinsonia last). Acacia aneura (Mulga) is an example of a tree that will produce blooms intermittently throughout the year. Acacia stenophylla (Shoestring Acacia) bloom heaviest in the spring but may also bloom periodically during the other seasons. Of these two species Mulga flowers are the most showy with numerous, small bright sulphur yellow, fluffy, cylindrical flowers. Summer color among desert species is far less abundant. Some of the best displays come from the Caesalpinia species, C.mexicana and C. gilliesii, with flower colors of bright yellow and yellow orange, respectively. Flowers are continually produced throughout the summer months. Another summer color option is Desert Willow which produce white to dark purple, orchid shaped flowers all through the summer. White and purple Vitex agnus-castus flowers develop slowly through a lengthy bloom season that extends from late spring into summer. Other summer bloomer include Smoke tree (Psorothamnus spinosus), Kidneywood (Eysenhardtia orthocarpa) and Ironwood (Olneya tesota). The Cascalote (Caesalpinia cacalaco) offers winter flowers. Highly fragrant species would include Sweet Acacia (Acacia smallii), Twisted Acacia (Acacia schaffneri), Acacia constricta (White Thorned Acacia), Texas Mountain Laurel (Sophora secundiflora), all the Pithecellobium species, Kidneywood and South American Palo Verde (Geoffroea decorticans). From spring through summer, all the mesquites produce elongate, fuzzy, drooping flowers. These flowers vary from pale yellow to tan. Some species that are not sufficiently appreciated for the beauty of their flowers include Ironwoods (small, pale to dark purple flowers), Pithecellobium pallens (abundant cream to pale yellow flowers), Acacia greggii (cream colored flowers) and creosote (bright yellow ball flowers). Desert tree species are pollinated by birds, wind, insects, ants or are simply self-pollinated. In placing flowering trees in the landscape consider that flowers and fruit are eventually shed and will produce some litter. With most species this litter is minimal and seeds are consumed by birds or other wildlife. Trees that produce larger flowers (e.g. Desert Willows) or that produce large numbers of flowers (e.g. Sweet Acacia) may not be suited for planting near a pool or water feature.