ZMT DDTOR: Daily Fact: What iconic cactus takes 50 years to grow one arm?

Original photo by LHBLLC/ Shutterstock

It can take 50 years for a saguaro cactus to grow one arm.

It's not easy to be a cactus — surviving in a scorching environment with little water is a pretty tough task for most plants. Some cacti, like the saguaro, have adapted by taking their sweet time to grow. In fact, saguaro cacti often reach just 1.5 inches in the first 10 years of their lives. Growing their iconic arms — often featured in old Western films and desert art landscapes — can take 50 years, or even up to 100 years in drought-like conditions.

Many saguaros do not flower until they reach 35 years old. And although they produce some 40 million seeds over their lifetime, odds are just one of their cacti descendants will survive to adulthood after battling arid conditions, trampling, human interference, and invasive species that threaten their environments. Reaching their maximum size — upwards of 45 feet tall and more than 2 tons in weight — can take 175 to 200 years, close to the end of a saguaro's lengthy life span. But there is perhaps one consolation involved in that long journey: Saguaros are the largest cactus species in the U.S.

These slow-growing giants are found wild only in the Sonoran Desert, which stretches from southeastern California across southwestern Arizona and into Mexico. Despite their vulnerabilities, saguaro are important plants in the Sonoran ecosystem, providing fruit for birds, nectar for bats and other pollinators, and superb nesting spots for birds and other wildlife — which is why these colossal cacti are legally protected native plants in Arizona.

Numbers Don't Lie

Height (in feet) of the largest recorded saguaro cactus

Estimated species of cacti globally

2,000

Species of cacti found wild outside the Americas

Diameter (in centimeters) of Blossfeldia liliputana, the world's smallest cactus

2.5

There's a special census for saguaro cacti every 10 years.

How do scientists know how many saguaros exist in the U.S.? Turns out, they count and record them, in a fashion similar to how the federal Census estimates the nation's population of humans. Scientists at Saguaro National Park in Arizona first began the cactus count in 1990 as a way to track species health and numbers, syncing the enumeration with the federal Census. Every 10 years, scientists and volunteers count the number of cacti in randomly selected areas of the park to calculate how many saguaro likely exist in the preserve as a whole. The work is labor-intensive, requiring census-takers to hike to desolate areas of the park and record each cactus' GPS coordinates, height, number of arms, and other information. In 2020, that work totaled more than 3,500 hours from staff and a group of more than 500 volunteers. The most recent report shows the saguaro population nearly doubled from the 1990 count, totaling around 2 million in 2020, though it's possible up to 20% of baby saguaro could be missed, since they're so small and difficult to spot.

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Daily Fact: What iconic cactus takes 50 years to grow one arm?