Arizona's iconic saguaro cactus: How fast they grow, how big they get and can you cut one?
The saguaro cactus may be the most recognizable plant in the Southwest. It’s so entwined with this region that it adorns buildings, logos, signs and license plates throughout Arizona. Its likeness has even become a symbol for other types of cactuses. Check your phone, there’s only one cactus emoji, and it's a saguaro.
But what exactly are these long-lived, many-armed giants? And why are they important to the Sonoran Desert?
The Arizona Republic talked to Ben Wilder, director and botanist at Tumamoc Hill Desert Laboratory at the University of Arizona in Tucson, an 860-acre national historical landmark that doubles as an ecological and archaeological reserve, to learn about saguaro cactuses.
And don’t forget, it’s pronounced suh-WAHR-oh.
What is a saguaro cactus?
According to Wilder, the saguaro is part of a large suite of cactuses called columnar cacti. They are called columnar for their shape. Characteristics of this genus include elongated and cylinder-shaped bodies, woody internal ribs that support their stature and prickly spines. Other species in the columnar cacti family include silver torch, totem and Mexican fence post varieties.
Where are saguaro cactus found?
Saguaro cactuses are exclusive to the Sonoran Desert. According to the Arizona-Sonora Desert Museum in Tucson, saguaros live in Arizona and western Sonora, Mexico. A few stray specimens may be found in southeast California.
“What makes the saguaro unique compared to other species in the group is that they are a lot more frost tolerant,” Wilder said. “They can handle freezing temperatures for up to 36 hours. Anything below would be dangerous.”
Their genetic elements and thousands of years of adaptation have helped saguaros flourish in this region where there are wide temperature swings, Wilder said. Their spines act as a buffer for both extremely hot and cold temperatures.
How long does it take a cactus to grow?
Saguaros grow slowly. A young cactus may grow just 1 to 1.5 inches in its first eight years of life.
The amount of water available affects their growth. Mature saguaros can weigh 3,200 to 4,800 pounds when fully hydrated, according to the Arizona-Sonora Desert Museum in Tucson.
Over decades, saguaros can grow to 50 feet or more. There is a strong relationship between age and height, meaning that saguaros grow at predictable rate, Wilder said.
The growth rate of saguaros is learned through long-term study at places like Tumamoc Hill, where over 6,000 saguaros have been studied, measured and monitored daily since 1908.
“With these long-term plots, like here on Tumamoc Hill, we're able to track individuals through time, and measure and re-measure and then re-measure again and determine their growth rate. And this is done on different habitat types, different slopes and in different regions,” Wilder said.
“Within the 100 years of data we have now here at Tumamoc Hill, I think it's been the fifth generation of scientists studying that data,” Wilder said.
What is the saguaro cactus lifespan?
Here's how a saguaro cactus grows from a seedling to a mature specimen.
- A saguaro starts as a seedling smaller than an eraser on a pencil. “The saguaro seedling, a little baby plant, is outrageously tiny for the first year, so much so that you have to be actively crawling on your hands and knees searching for them,” Wilder said.
- At 3 to 4 years old, they become more visible. After that, they grow faster but don't start branching until they are 20 to 30 years old. At that age they become sexually mature and start producing flowers and fruit.
- Then they start putting energy into growing arms and increasing their reproductive capacity for about 70 years. An adult saguaro can reach 50 feet or more in height.
What is a crested saguaro?
Instead of growing in the shape of a column, the tops of some saguaros broaden and develop into a fanlike formation. Saguaros that exhibit this irregular shape are known as crested saguaros.
The crested growth form is not unique to saguaros, Wilder said. It also occurs in barrel and other columnar cacti.
“It's seen across the cactus family and we don't definitively know what causes it,” Wilder said.
There are two main theories, he said. The first is that the crested shape is a simply genetic response that occurs on some cactuses. The other is that it's a response to a disruption of the plant's apical growing stem. This structure is a region of cells in a plant's roots or shoot tips that are capable of division and growth, according to Britannica.com.
Saguaros are significant to Indigenous people
Saguaros live to about 200 years old on average. So how are they studied when they exceed the lifespan of a human?
Wilder said the relationship between Indigenous people and saguaros far exceeds what scientists think they know about these giant plants.
“From a Western science perspective, we need to have a lot of humility and recognition of the fact that our longest data set runs about the span of about half of an average lifespan of a single saguaro,” Wilder said.
“So we think we know a lot about these species and these plants, which we do, but relative to the relationship, observation and direct core cultural interaction that many Indigenous communities throughout the region have had with these plant for centuries prior, especially that of the Tohono O’odham, who consider this plant sacred, their understanding I think far eclipses that of a scientist.”
What is the saguaro's role in the environment?
The saguaro plays an important role in its environment. Woodpeckers and other small birds excavate nest cavities in the saguaro’s flesh for shelter. Other birds build nests along the arms. And in the driest times of the year, the saguaro produces flowers and fruit — important resources for all kinds of wildlife in the hot summer months.
“Just thinking about the flowering alone that happens every year and at the driest time of the year, that is such a critical resource for so much wildlife like pollinators and other animals," Wilder said. "Their flowers become this nectar, water and pollen food source. So the saguaro becomes like this little food oasis in the middle of a parched desert.”
Wilder said saguaros are a keystone species — one that other species in an ecosystem depend on — but they are not dominant. Saguaros benefit from other keystone species. Paloverdes, mesquites and ironwoods act as nurse trees to baby saguaros. These trees create little microenvironments underneath their canopies where it's cooler in summer and warmer in winter and baby saguaros can thrive.
“There’s is such a great interconnectedness between species that pervades throughout the desert,” Wilder said.
What is a saguaro cactus flower?
Saguaros typically flower near the tips of their arms, in contrast to other species of columnar cacti that flower all up and down their trunks and stems, Wilder said. Once the flowers have been pollinated, which occurs within 24 hours, the flowers mature into fruit.
Last year, some saguaros exhibited unusual side blooms lower down their trunks. Wilder says that's a rare occurrence.
“We think that happened last year because of the extreme drought that we had in 2020, which essentially triggered the saguaro into trying to flower again in August after already doing so in June, Wilder said.
Is it illegal to cut a cactus?
The growing human population, land development, theft and vandalism are some of the biggest threats to saguaros, according to the National Park Service. That's why many plants —including saguaros — are protected under Arizona's native plant law.
Destruction or theft of a saguaro is illegal under Arizona law and can result in fines and a Class 4 felony conviction. Arizona law says that landowners can destroy or remove plants on their land, but only if the land is privately owned and protected plants are not taken off the land or offered for sale. The law requires that the landowner notify the state 20 to 60 days before the plants are destroyed.
Are saguaros endangered?
Wilder said it's important to look at the future of Saguaros in a big picture and realize that Saguaros know a lot about how to live in this region.
“I believe that saguaros are a wonderful example of adaptation to the boom and bust cycles of the desert environment,” Wilder said. “When we experienced the drought in 2020, they were getting very stressed but weathered it, but we did see older individuals perish. Then last year there was this extreme monsoon.”
While saguaros have adapted to the waves of heat, cold, drought and rain, the effects of extended dry and hot weather are something to keep in mind, Wilder said.
Another threat to saguaros is wildfire, often fueled by invasive species. Fires such as the 2020 Bush Fire scar the landscape and kill large numbers of saguaros, especially young ones. Wilder said young saguaros cannot survive wildfires and new cohorts of saguaros cannot get established in large burn areas.
"The importance of trying to mitigate the spread of invasive species when feasible and to put resources to do so sooner than later is important to the future of saguaros," Wilder said.
Cactuses and wildfire:What the Bush Fire could mean for Arizona's iconic saguaro
Support local journalism like this story by subscribing today.