Plant of the Week
Saguaro (Carnegiea gigantea)
By Charlie McDonald
Along with the howling coyote, roadrunner, and chili pepper, the saguaro (pronounced suh-WAR-oh) cactus is one of the enduring symbols of the desert Southwest. It has been immortalized in art, cinema, and advertising often juxtaposed into settings where it could never truly exist.
Actually, saguaros grow in a rather narrow slice of the Sonoran Desert in Arizona, Mexico, and a small part of California. They need rocky soils for good root anchorage, more moisture than is normal in the low deserts, and mild temperatures without any prolonged freezing. These conditions are found on bajadas that form the lower slopes of desert mountain ranges. Some of the best saguaro habitat is found on national forests. Magnificent stands of these giant cacti can be seen north and east of Phoenix in the New River, Mazatzal, and Superstition mountains on the Tonto National Forest. Equally impressive stands can be seen north of Tucson in the Santa Catalina Mountains on the Coronado National Forest.
A typical saguaro is both old and huge. Plants are at least 50 years old before they flower for the first time and usually about 75 years old when the first side branches develop. Plants can live for 200 years. A giant saguaro can reach almost 50 feet in height and 10 feet in circumference. They are by far the tallest plants in their desert scrub environment. A large plant full of water can weigh up to 6 tons.
The saguaro is a keystone species that provides food and shelter for many desert animals. Saguaros have hundreds of flowers that bloom several per day from late April to early June. The flowers open at night and close the following afternoon. Lesser long-nosed bats visit the flowers at night. Birds, mostly white-winged doves, and insects, mostly honey bees, visit the flowers the following morning. The fruits mature in June and early July. The rind splits into three or four sections that peel back to expose the juicy red pulp embedded with up to 2,000 tiny seeds. The fruits ripen during the peak of drought in the early summer and are about the only moist food source for many birds, mammals, and insects during this part of the year.
Saguaros make excellent nesting places for many birds. Gila woodpeckers and gilded flickers both excavate nest holes in the fleshy stems. The woodpeckers usually excavate new nest holes each year giving other birds like elf owls, house finches, ash-throated flycatchers, and purple martins an opportunity to occupy old woodpecker nests. Red-tailed hawks and other large birds nest in the angles between the main stems and the arms. Tall saguaros make good hunting and resting perches for many birds.