In April, buds looking for all the world like Brussels sprouts appear on the trunks and uplifted arms of mature saguaro plants.
Opening in early May into crowns of glorious large white flowers, these night bloomers remain open until noon or early afternoon of the next day, their deep nectaries and pollen-laden anthers unfolded to nighttime pollinators and daytime pollinators alike.
The pollen grains of the saguaro are too large to be windborne, so the saguaro must be cross-pollinated by creatures conned to the job by the sweet smell of night perfume and the generous store of sugary nectar the saguaro produces so abundantly.
The most important fertilization takes place at night.
Nectar-feeding, long-nosed bats (recently put on the endangered species list) make their annual migration up from Mexico, arriving on schedule just as the saguaros are blooming.
Hovering over a saguaro flower like a giant moth, they plunge into the dense thicket of stamens feeding on nectar and pollen, emerging well-coated with snowy pollen before clambering into another flower, dispersing and picking up pollen as they flit from flower to flower.
Domestic and wild bees submerge themselves into the petals and reappear with the fat little bottoms well dusted with pollen, as they go on to bury themselves in flower after flower.
The white-winged doves, after wintering in Mexico, arrive in Arizona just in time to join in the raids on the honey-sweet flowers.
Curved billed thrashers, cactus wrens, Gila woodpeckers, and gilded flickers all feed on saguaro flowers and do their share of pollinating, but the white-winged dove, more numerous than the others, do the greatest share, guzzling nectar all the way.
It is with good reason the range of the white-winged dove in Arizona is almost identical with the range of the saguaros.
About a month after the flowers appear the fruit is ripe. In the mounting heat of June and July the fruit opens, fresh and red and juicy, splitting three or four ways, like giant petals. The birds have a field day.
White-winged doves predominate, but all the desert birds dine on the fruit while they are still on the plant. Gambel’s Quail fly higher to get at the fruit than they fly at any other time.
The fruit falls to the ground and is eaten by coyotes, pack rats, quail, brown towhees, the cactus mouse, antelope ground squirrels, rabbits, etc. Harvester ants carry off the seeds to their underground chambers, clearing off the area below a saguaro in record time.
The life of a saguaro seedling is no breeze; it is full of hazards all the way. The more knowledge scientists have amassed the more wonder it is that we have any saguaros at all.
From 10,000 seeds fallen to the ground, with an average life expectancy of six weeks, maybe one will put down roots.
For a seed to germinate at all it must rain two times within five days. Such stringent circumstances are hard to come by. It happens on an average only once in every 25 to 30 years. Only four years in the last century have been favorable for saguaro seedlings: 1900, 1929, 1941, and 1967.
During an active reproductive life span of 100 years, a healthy saguaro will produce 40,000,000 seeds, with an average 2,000 seeds to each fruit. Researchers estimate that for the species to endure, only one of those 40,000,000 seeds must germinate and survive to become productive.
That seed must fall on a rocky hillside or under the protection of a nurse plant (a bursage or a palo verde) which will protect the seedling from being fried by the summer sun, from the freezes that come upon us, from marauding rodents hungry for a wisp of green, or from being mashed under the heavy foot of a cow, out on the desert where man has pushed his cattle into land that cannot support grazing.
A saguaro a year old takes up only a cubic inch of living space, and will be only an inch tall.
Growth is very slow. A young saguaro 20 years old may be only a foot and a half high, and that’s under favorable circumstances. The rate of growth varies, dependent in a large amount on summer rainfall.
The hottest weeks of the summer, the six weeks to two months in July and August, if the expected summer rainfall materializes, will see the greatest growth of the saguaro. These are the important weeks. After the rains cease, no further growth occurs.
The saguaro will be 50 to 70 years old before it produces its first flower, to start the precarious cycle all over again. It is a wonder we have any saguaros at all.