Saguaro Growth

How Old is That Saguaro?

Across all ecosystems, different species have different ways of telling us their age. For instance, many people know that trees can be dated by counting their rings. However, the saguaro cactus does not hold this information in a way that we can see. There is no way to tell the exact age of a saguaro without knowing when it took root as a seedling and started growing.

While we cannot know the precise age of each saguaro, we can make educated estimates based on a number of factors throughout their life cycle. Keep in mind that growth rates vary depending on rainfall, temperature, soil conditions and various other factors, even within a given population. Thus, different regions will have different saguaro growth rates. For example, the Tucson Mountain District (west) of the park receives much less rainfall than the Rincon Mountain District (east), and the saguaros seeing less rainfall will inevitably grow at a slower rate.

 

In their first few years, saguaros are nearly impossible to find unless you have a keen eye.

NPS photo

A Few Inches Tall

How tall were you when you were 5 years old? What about 10 years old? When a saguaro is a mere 1 to 3 inches tall, it is somewhere around 5 to 10 years old. Because they are so small in their first 10 years, it is incredibly difficult to find a saguaro at this age, so consider yourself lucky if you do! The first 10 years of a saguaro's life are crucial to the saguaro's success as it continues to grow and establish itself in the soil. At 10 years old, a saguaro is incredibly vulnerable to a number of elemental factors such as wind, sun, harsh temperatures and trampling.

Two Feet Tall

When a saguaro is 2 feet in height, it can be anywhere from 20 to 40 years old. At this point in its life, the saguaro is about to hit a growth spurt!

 

If a saguaro has flowers, you know it is at least 35 years old!

NPS photo/TWiewel

Six Feet Tall

When a saguaro is 6 to 8 feet tall, it is 35 to 70 years old. The large range of this estimated age is due to the differences in growth rates depending on environmental factors the saguaros experience. For example, a saguaro growing in the Tucson Mountain District (west) of the park will not see as much rainfall as one in the Rincon Mountain District (east), so it may be as old as 70 when it is only 6 feet tall. When a saguaro is of this height and age, it is ready to start producing flowers! The first saguaro blooms are seen in late April, and they continue to bloom through mid-June. Saguaro flowers create a crown on the top of the saguaro, and each individual flower is only open for 18 - 24 hours. This small window of time is when the flowers are being pollinated by birds, bats and bees. Saguaro National Park monitors these blooms each season to gain more insight into the various trends we see occuring during that time. Learn more about saguaro flower studies.

 

The more arms a saguaro has, the more successful it will be at reproduction.

NPS Photo/TWiewel

Eight to Twenty Feet Tall

At this height, the saguaro will start pushing out its arms. However, not every saguaro will begin producing arms as soon as it is able to do so. Though it is rare, some saguaros may choose to never grow arms. In fact, the tallest saguaro ever recorded was 78 feet tall, and it had zero arms!

Saguaro arms are important for reproduction of the plant as each arm is able to produce its own set of flowers and fruits. Thus, saguaros with more arms are producing that many more seeds. Each saguaro is unique, and not every one grows its arms in the same way or at the same rate. There are a number of trends we see with arm growth, and the park continues to study aspects of arms such as arm symmetry and direction of growth.

 

Wander around long enough, and you will find giants across the desert.

NPS Photo

Maturity and Old Age

As saguaros get older, most will continue to grow in by producing more arms. The saguaros keep pushing on in life, and healthy saguaros will grow to be 40 feet in height and sometimes over 150 years old! As saguaros approach older age, you will notice discoloration, scarring, loss of spines or various other signs of a life long lived. At Saguaro National Park, there is not one specific saguaro that is known to be the oldest or largest, but you will find these giants throughout the cactus forest.

 

NPS Photo/TWiewel

Death

Causes of death among saguaros include lightning strikes, blowdown events, catastrophic freezes, and bacterial necrosis. However, most saguaros live long lives and die simply due to old age. When a saguaro dies, its outer layer will begin to decay, exposing the ribs (or skeleton) on the inside. Saguaro skeletons are sometimes seen still rooted in the earth, whereas others may topple over in death and be found laying across the ground. Either way, while the flesh decays, the saguaro skeleton is left to stay for many years to follow.