I thought I would add this page to the group to explain the answer to a very common question (sometimes complaint) that I receive. "How come you can't predict exactly when the wildflowers will bloom and how many blossems we will get each year?" From my own personal experience as a beekeeper and as a Life Science Instructor and from a publication by Mark Dimmitt, called; Predicting Desert Wildflower Blooms - The science behind the spectacle. (Which I Am Copying Here) (Mark says it better than I could do) I would say that: Desert annual wildflower blooms are nearly impossible to predict for two reasons: 1. The necessary conditions are not precisely known. 2. Many interacting variables affect the phenomenon. What we do know: Spring-blooming annuals must germinate in the autumn. This is a crucial fact that most people don't know. The "critical window" is probably between late September and early December, but differs with different species. The controlling environmental factor is temperature. A "triggering rain" of at least one inch must occur during this autumn window, the earlier the better after summer heat has waned. Rains at other times will seldom trigger germination of the showy-flowered species. The triggering rain must be followed by regular rains totaling at least an inch per month through March, a season total of at least five inches, seven or eight are better. In short, a really good wildflower bloom requires both an unusually early and an unusually wet winter rainy season. The rains must also be well spaced. Spectacular, widespread shows occur about once in 10 years in the Sonoran and Mohave Deserts. Good or better displays occur in localized areas perhaps every three or four years; these may be in remote regions and go unnoticed. However, even when all the above conditions are met, the bloom may be mediocre or poor. And occasionally a good bloom occurs when the above conditions appear not to have been met. The latter can happen when an unusually warm rain triggers germination in winter, but the short growing season usually precludes a really good show. Factors which are suspected of preventing a show include: a few weeks of warm, windy weather; the water stress triggers premature flowering; a cold winter that retards growth of the seedlings; high population levels of herbivores such as rodents, rabbits, quail, or insects; a wet preceding summer, resulting in thick growth of summer vegetation, which in turn prevents germination of winter annuals. When it does happen, the peak typically lasts only two weeks at a given location, sometime between late February and mid April. Most often it happens in early to mid March. Furthermore, only certain areas ever have mass displays; soil type and vegetation cover are important factors. The rocky and densely-vegetated Tucson Mountains rarely if ever have mass blooms, whereas Picacho Peak and the Tohono O'odham (Papago) Indian Reservation do fairly regularly. The above information pertains only to annual wildflowers (poppies, lupines, owl clover, etc.) Perennials are less fussy about the timing of rainfall. Thus a late but wet rainy season can still produce good blooms of penstemon, larkspur, brittlebush, etc. Some plants such as palo verdes, ocotillo, and most cacti flower every year regardless of rainfall. (See Desert Flowering Seasons for details.) But it is the annuals alone that produce the desert's famous carpets of color. The Spring Flowering Season in the Arizona Upland subdivision spans from mid February to mid June with a peak from mid March to late April depending on rainfall and temperatures during the growing season. In the warmest areas of the Lower Colorado River Valley subdivision it is normally a couple of weeks earlier, though it sometimes starts as early as November. The different life forms which dominate at different times vary in their showiness and reliability. The early-blooming winter annuals can create an incredible display, but do so only rarely. Later-blooming species bloom more dependably, but mostly not in great masses of color. The progression of spring bloom described below is for average years near Tucson. It may be three weeks earlier or later depending on weather, elevation, and latitude. Winter Annuals Winter annuals such as poppies (Eschscholtzia mexicana), lupines (Lupinus sparsiflorus and others), and owl clover (Castilleja exserta, syn. Orthocarpus purpurascens) create the vast carpets of color for which the Sonoran and Mohave deserts are so famous. This event may occur between late February and mid April, usually in mid March. Annuals are highly dependent on rainfall. Massive and widespread displays occur only about once a decade, when the winter rainy season is both earlier and wetter than normal. Good shows happen in localized areas every three or four years. A good bloom cannot be reliably predicted more than a week or two before it begins (see next page for details), and it lasts at peak beauty for no more than two weeks. Seeing one requires being able to travel on short notice, and perhaps great distances. Death Valley may be spectacular in a year when Organpipe Cactus National Monument is poor. The high Mohave Desert may peak two or three weeks later than the lower elevation and more southerly Sonoran Desert. A good bloom may occur in a remote area and remain undiscovered. Herbaceous Perennials and Small Shrubs Herbaceous perennials and small shrubs such as penstemon (especially Penstemon parryi), brittlebush (Encelia farinosa), and fairy duster (Calliandra eriophylla) also require rain to bloom but are less sensitive to its timing. They are somewhat more dependable than the annuals, making a good show in about half of the years and peaking some time in March. These species usually grow as individuals or in small patches and do not create masses of color. Cacti Cacti, because they store water, are fairly independent of rain. They bloom well nearly every year though wetter years produce more flowers. The greatest diversity of spring-blooming species can be seen in April. The cactus show continues as the abundant prickly pears bloom in early May, followed by saguaros from mid May to mid June. Trees and Large Shrubs Trees and large shrubs are fairly dependable bloomers, though flowers will be sparse in dry years. Creosote bush (Larrea tridentata) and whitethorn acacia (Acacia constricta) both bloom mainly in spring and sometimes again in summer. Blue palo verdes (Cercidium floridum) turn bright yellow in late April, followed two weeks later by the much more abundant but paler yellow foothill palo verdes (C. microphyllum). Desert ironwood trees (Olneya tesota) bloom heavily about every other year with masses of lavender flowers, usually in late May. The abundant ocotillo reliably produces spikes of red flowers through-out April. These species bloom about two weeks earlier in western Arizona. Summary If you want to see the famous carpets of color, keep abreast of local news from Palm Springs to Tucson and from Death Valley to northern Mexico. Begin checking in January lest you miss an early show. (The dunes can sometimes begin in November, but this catches nearly everyone off guard so it's pure luck to discover such an early show.) You'll find masses of annuals somewhere in this area about once every three or four years. If you want dependability and will settle for less quantity, success is almost guaranteed in the middle half of April. Summer Flowering Season The summer flowering season season begins a few weeks after the first summer rain and continues into late fall. Though there are many beautiful species to be seen, there are rarely massive displays of color in this season, because the summer rains are more sporadic and localized than the winter rains and the soil dries rapidly in the heat. Summer Annuals Summer annuals such as summer poppy (Kallstroemia grandiflora) and devil's claw (Proboscidea parviflora) germinate within a few days after the first soaking summer rain and begin to flower as soon as three weeks later. Chinchweed (Pectis papposa) is the most widely-adapted summer annual; it ranges from New Mexico into the central Mohave Desert where it is the only summer annual (summer rains are uncommon in the Mohave). It can form showy carpets of yellow when rains are abundant. Herbaceous Perennials and Small Shrubs Herbaceous perennials and small shrubs bloom opportunistically if they get enough rain. Trailing four-o'clock (Allionia incarnata) and desert marigold (Baileya multiradiata) are nonseasonal, flowering in response to rain in all but the coldest months. Fairy duster will also bloom again in wet summers, but not as profusely as in spring. Sacred datura (Datura wrightii) is mainly a summer perennial though it may begin flowering as early as April in warmer areas. There are several woody shrubs that bloom in late fall. Most are composites such as burroweed (Isocoma tenuisecta) and desert broom (Baccharis sarothroides). Desert senna (Senna covesii) and Coulter hibiscus (Hibiscus coulteri) flower in response to any warm rain and peak in summer when most such rain occurs. Desert zinnia (Zinnia pumila) is truly biseasonal, flowering well in both rainy seasons. Cacti Cacti include several summer-flowering species. The pincushion cactus Mammillaria grahamii microcarpa makes buds during its previous growing season, then goes dormant during the dry season. The buds burst into bloom five days after each of the first two or three summer rains. The fishhook barrel cactus (Ferocactus wislizeni) is much larger thn the pincushion and less dependent on rain; it flowers throughout August and September. Trees and Large Shrubs Trees and large shrubs are nearly all spring bloomers, but a few bloom again in summer if rains are generous. Whitethorn acacia (Acacia constricta), velvet mesquite (Prosopis velutina) flower heavily in spring and often again in summer. Desert willow (Chilopsis linearis) flowers from spring through fall if it has enough water. Summary Though the Sonoran Desert has two flowering peaks, there is almost always something in bloom. The only exceptions are after a hard winter freeze or during severe droughts. Other pages will follow. See links at botttom of page. |