The saguaro often referred to as the giant cactus, has long been an emblem of the American southwest.

These towering plants are easily identifiable by their impressive size and shape, with some growing as tall as 50 feet.

Where Do Saguaros Grow?

The saguaro cactus (Carnegiea gigantea) is native to the Sonoran Desert, but it doesn't grow everywhere within this vast region. Saguaros thrive in areas that offer a perfect balance of heat and rainfall. Freezing temperatures can severely damage these plants, making climate a key factor in determining where they can grow. As such, they are confined mostly to central Arizona and northern Sonora, Mexico.

Because saguaros are sensitive to cold, their growth is also limited by elevation. Typically found at altitudes ranging from sea level up to 4,500 feet, they can sometimes be found growing as high as 5,000 feet on south-facing slopes, where freezing temperatures are less common.

Saguaro Growth

Saguaros are incredibly slow-growing. In Saguaro National Park, they may only grow a few inches in the first ten years of life. As young saguaros are often hard to find, they take shelter under nurse trees like palo verde, mesquite, or ironwood, which protect them from the harsh sun and cold temperatures. As they age, saguaros growth rates vary depending on local climate and rainfall.

At Saguaro National Park, most saguaros begin to grow branches when they are 60 to 75 years old, although it may take up to 100 years in drier areas. They start producing flowers around 35 years of age, which appear mainly at the tips of the main trunk and branches. Saguaros are typically around 125 years old, weighing several tons and growing up to 50 feet tall. Some can live to be 150-175 years old, with a few possibly reaching over 200 years.

Why Are Saguaros Pleated?

Saguaro cacti are characterized by their pleated skin. This unique structure helps them store water during periods of heavy rainfall. The pleats expand like an accordion when the cactus absorbs water and contract as the plant uses it's stored moisture during dry spells. Because the saguaro is mostly water, a large one can weigh as much as 80 pounds per foot of it's main trunk.

Crested Saguaros

Saguaro cacti sometimes grow in unusual, misshapen forms. A rare phenomenon, known as fasciation, causes the growing tip of the saguaro to form a fan-like shape, creating what is called a crested or cristate saguaro. Though the exact cause of this abnormal growth is unknown, it is believed to be linked to damage to the growing tip.

Wildlife Interaction

Saguaro cacti are home to a wide range of wildlife. Birds like the gilded flicker and Gila woodpecker excavate nesting cavities in the cactus’s soft flesh. When these birds abandon their nests, other species like elf owls, screech owls, and sparrows may move in. Larger birds, such as red-tailed hawks, use saguaros for nesting and hunting platforms, building their stick nests among the cactus's arms.

Saguaro cacti also provide vital food for desert wildlife. During the summer, the ripening fruit offers a rich source of moisture and energy at a time when other food may be scarce. In the drier regions of the Sonoran Desert, animals like pack rats, jackrabbits, mule deer, and bighorn sheep will feed on the cactus’s flesh when other resources are not available.

Reproduction

From late April to early June, the tops of a saguaro's trunk and arms bloom with large, creamy white flowers. These flowers open at night and close the following afternoon, and for them to develop into fruits, they must be pollinated within this short window. Pollination is carried out by nectar-feeding bats, birds, and insects.

Each fruit contains between 2,000 and 3,500 tiny black seeds. When the fruit and seeds are consumed by animals like coyotes or cactus wrens, the seeds pass through their digestive systems unharmed and are spread across the desert. However, if a dove or quail eats the seeds, they are fully digested. Over it's lifetime, a saguaro may produce between 20 and 40 million seeds, though only a small fraction will survive to become seedlings.

Do Humans Use the Saguaro?

Archaeological evidence shows that early desert inhabitants used the saguaro cactus in various aspects of daily life. The strong, wood ribs were harvested to build the framework of homes, while the ribs were also used to create long poles for gathering saguaro fruit. The seeds are also used as chicken feed.