Lesson Plan

How Much Water Can Sunny The Saguaro Drink?

A desert landscape with saguaro cactus, prickly pear, and cholla and thunderclouds in the background

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Grade Level:
High School: Ninth Grade through Twelfth Grade
Lesson Duration:
90 Minutes


How does Sunny the Saguaro's age over the years compare to his height? The objective of this lesson is to help students learn about the relationship between the height of saguaros and their age while utilizing their geometric equations to calculate the volume of Sunny the Saguaro.


The saguaro has been called the monarch of the Sonoran Desert, supreme symbol of the American Southwest, and a plant with personality. It is renowned for the variety of odd, all-too-human shapes it assumes- shapes that inspire wild and fanciful imaginings. Since 1933 this extra ordinary giant cactus has been protected within Saguaro National Park.

Saguaros collect water through shallow roots extending about as far outward as the main trunk is tall. As saguaros soak up water, accordion-like pleats in the trunk and arms expand to allow for storage in the spongy flesh. Waxy skin reduces moisture loss. Spines shade the plant, shield it from drying winds, and discourage damage from animals.

Sunny the Saguaro has been the Park’s official mascot since 2016. You can find him at different park events such as Find Your Park or you can see him hanging out with Jr. Rangers during one of the Jr. Ranger programs held every summer.


Learn more about Saguaro National Park.

Print the Saguaro Worksheet and Saguaro Height-to-Age table for the students.



Contains saguaro volume student worksheet

Download Saguaro Volume Student Worksheet

Contains saguaro height-to-age data collected from the Rincon Mountain District.

Download Saguaro Height-to-Age Table

Lesson Hook/Preview

Rumors have it that Sunny the Saguaro is a one tall cactus! But who knows what his actual height might be? Desert animals speculate that he might be between 6 to 40 feet tall! However, the park rangers are more curious about how much water Sunny can drink to fill himself up. 

As far as Sunny can remember he was 3 inches tall when he was 10 years old, 3 feet tall when he was 25 years old, and 16 feet tall when he was 60 years old! Now, sunny is 20 feet tall and still growing!

Can you estimate how old Sunny the Saguaro is based on his height? Using his height, can you estimate how much water it will take to fill Sunny? Assume that Sunny is 100% water inside.



#1: Talk to students about Saguaro National Park.

#2: Show a photo of saguaros with different height and ask what could be the age of each.

#3: Given that Sunny is 20 feet tall, ask students how old Sunny might be.

#4 Using the Saguaro Height-to-Age table, figure out Sunny's approximate age. After, a
sk what shape Sunny resembles—hint: it’s a cylinder!

#5: Discuss how to calculate the volume of a cylinder and provide the formula needed for doing so. The formula is V = π•r2•h where r is the radius and h is the height.

#6: Provide students with a measurement of the circumference of the saguaro. Sunny is 18 inches wide. 

#7: Have students calculate the answer. How much water can Sunny the Saguaro drink?


Volume- how much space an object occupies, usually expressed in cubic units
Circumference- the distance around an object
Radius- a line that starts from the center of a circle and ends at the circumference of it
Cylinder- a geometric figure that has parallel sides that connects to a round top and bottom. Ex. can of beans
Saguaro- a giant columnar (cylindrical) cacti that is native to the Sonoran Desert

Related Lessons or Education Materials

This lesson was originally created by Wyoming Agriculture in the Classroom and inspired by Devils Tower Math- Volume of a Cylinder by Devils Tower National Monument.

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Last updated: December 19, 2018