You might assume that a cactus that is several feet tall must be older than another one that is only a few inches tall, but this is not a good way to estimate a cactus’ age.
Unlike a tree, which has annual rings that can tell you how old it is, cacti do not have this feature to help you tell their age.
The best you can do is rely on other factors to give you an estimate of a cactus’ age. These include the size and the height of the cactus relative to its species, the number of areoles, and the cactus’ growing conditions.
In this article, we will discuss how to accurately estimate the age of a cactus. If you have a cactus that has been in your family a long time and you want to know how old it is, keep reading and let us try to figure it out together.
Why does a cactus not have growth rings?
Cacti do not have growth rings because, unlike trees, they have tissue that stores water to help keep them alive. This surrounds bundles of vascular tissue found in the very center of the cactus.
The rings on trees are lignified vascular tissue that increment each year. Cacti do not have this, probably because of their dry living environments.
Trees in subtropical and temperate latitudes have more pronounced growth rings because the seasonal changes also cause a change in the trees’ speed of growth. This is because there is a big difference in water availability between the rainy and dry seasons, as well as the difference in temperature between winter and spring.
Trees grow more during the rainy season and significantly less over dry periods, and the contrast in cell wall thickness can be observed in the growth rings.
How to tell the age of a cactus
The water the cactus receives in its habitat
One main factor that can help estimate the age of a cactus is the amount of precipitation it receives.
Some cacti that live in environments with lots of rain, like the prickly pear cactus, grow quite quickly and will outgrow their space in a fairly short time.
Compare those cacti to the ones that grow in deserts, where they only get around three inches of rain in a year. These water-deprived cacti can grow very slowly.
Size or height of the cactus
There are thousands of cactus species that are native to different parts of the world. Each of these has a different speed of growth.
Each cactus species needs to be studied for multiple years to correctly determine how much it grows in a year.
Typically, the columnar type of cactus will grow more in a year than a barrel cactus. An example of a columnar cactus is the Saguaro Cactus, which can be around 16 feet when it is a hundred years old. A Golden Barrel Cactus, on the other hand, is only around eight feet tall at a hundred years old.
On the assumption that Saguaro Cacti grow around eight inches per year, a 78-foot-tall Saguaro Cactus would be around 150 years old.
The size and height of a cactus can be a good gauge for age, but there simply is not enough data to prove that this is an accurate method.
This method might be quite accurate for the Saguaro Cactus, but the same cannot necessarily be said for other cactus species.
The number of areoles on the cactus
Another method that some people use to determine the age of a cactus is the number of areoles on the plant.
An areole on a cactus is where its clusters of thorns grow from, and is also where flowers or even a new arm will sprout from.
Younger thorns less than a year old are red in color. These thorns will grow row by row, so that those at the top are younger than those found at the bottom.
The number of arms
This method is usually used for column-type cacti. Some people use the number of thorny arms branching from the cactus’ main stem to indicate the age of the cactus.
The Saguaro Cactus, for example, will not start to grow arms until it is at least 70 years old. As an estimate, a Saguaro Cactus that has one fully-grown arm is around 100 years old. When the cactus has multiple fully-grown arms and even flowers, it is typically assumed to be at least 150 years old.
Unfortunately, this method cannot be applied to cacti that do not grow arms.
Can a cactus die from old age?
Cacti are very difficult to kill, which is also why they are one of the very few types of plants that can survive in the kinds of environments where they grow.
Some cacti that are estimated to be over 150 years old are not even considered fully-grown yet. These cacti can live to be over 200 years old.
Cacti are more likely to die due to damage from the elements or animals than from old age.
Accurately determining the age of a cactus can be difficult if you do not have access to high-end technology in a laboratory that specializes in these plants.
However, you can try estimating the age of a cactus by considering a few factors that can give you a ballpark estimate.
These factors include the amount of precipitation the cactus receives in a year, the size and height of the plant, the number of areoles, and the number of arms on the cactus.
These factors may not provide you with as close a guess as the rings on a tree might, but they are a good means of estimating the number of decades a cactus has been alive.
Image: istockphoto.com / Boyloso