Saguaro You Today?

By: Tom Gatz, Garden Docent and Horticulture Aide

There is a bumper sticker greeting you will find in All About Saguaros, the title of an Arizona Highways book by Leo W. Banks, published in 2008 and available in the Desert Botanical Garden gift shop. Here is just a sampling of the information in this helpful book:

• Human beings lived in Arizona before saguaros did. Saguaros colonized our warming landscape only about 10,000 years ago.
• Saguaro roots extend out to a distance about equal to the height of the plant and, in some cases, two times beyond.
• Saguaros can split from too much water and can literally explode if directly hit by lightning.
• A month after the first summer rains, the diameter of the saguaro can increase by 50 percent.
• Spines on a young saguaro are thicker than those on a mature cactus and keep it as much as 70 percent in the shade.
• Many saguaros start “thinking” about reproduction at about the age that most humans start to think about retirement (50-60 years old).
• Saguaro flowers have more stamens (the yellow male filaments with pollen) than any other desert cactus flower.
• Saguaro flowers produce nectar in two waves; the first peaks about 10 pm to attract nectar-feeding bats, if any are within its range. After dropping off by midnight, it picks up again just before dawn to attract insects and birds. The efficient bees usually remove all of the remaining pollen by 10 am.
• For a saguaro forest to maintain a consistent population size over time, on average only one of the millions of seeds produced by each saguaro in its lifetime will need to survive to maturity.
• A saguaro seed will last only a few months in the soil bank (mesquite seeds, in comparison, survive for years).
• In the cooler parts of their range, dark rocks that hold heat actually provide better shelter for seedling saguaros than do desert trees.
• Saguaro cavities are the only known nesting habitat of the desert race of the purple martin, a species of swallow.
• Urban saguaros become pockmarked with cavities when woodpeckers are forced to re-nest over and over again due to their cavities being usurped by the aggressive European starling. Too many cavities can allow frost to invade and significantly damage the center of the stem.
• Fire carried by contiguous stands of nonnative buffel grass poses the greatest threat to the future of our saguaro forests.
• Numbers often cause the readers eyes to glaze over, so instead of telling them that a 35-foot-tall saguaro with six or seven arms weighs over 7 ½ tons or 14,000 pounds, the author paints a mental picture that they will be more likely to remember such as: A big saguaro can weigh as much as two Hummers filled with families, dogs, camping gear, and in-laws.

The author also mentions that the tallest species of cactus in the world may not be the saguaro (53 feet), nor the cardon (65 feet), but is possibly the up to 82-foot-tall Pachycereus grandis, a close relative of the cardon found in central Mexico. However, several columnar cactus authorities have questioned whether P. grandis actually gets this tall.

And the next time my wife Barbara asks me if I’m asleep, I’ll reply, “No I’m just Sonoran.”

Thanks to Dr. Joe McAuliffe, Judi Irons, Matt Johnson, and Tina Wilson for reviewing earlier drafts of this article. Reprinted with permission from The Gatherings, the volunteer newsletter of the Desert Botanical Garden.