The first thing most people do wrong with a saguaro: Guess its age. It looks like a tree. If you’re used to trees, you think you can estimate age the same way. You might try counting rings or assuming that age follows a straight line from height, but neither work.
In fact, saguaros age on their own timetable, as the chart indicates; it’s not a matter of calendar years so much as of biological events such as branching out and flowering. Knowing that helps you tend potted ones… Or wild ones, better.
How to Tell a Cactus Age
A Saguaro begins flowering at about age 35, when it might be only six feet high. It doesn’t really get bigger than perhaps twenty feet until maybe forty more years later. This means that, as with most plants, growth is slow, sometimes not much more than an inch a year. A fifty-year-old Saguaro are just reaching sexual maturity; a ten-year-old is hardly out of infancy.
Many people think that because a tree or shrub is large they know how old it must be. In the case of the Saguaro, they may be looking at a young adult (in cactus terms).
Growing cacti in containers on your porch is very different than their wild desert habitat, which is why potted specimens will also follow a different time line. While a golden barrel in a pot may flower in five years, the one in the wild will wait, and even then have much more life ahead.
For instance, a fishhook barrel cactus can lives for more than 100 years in the wild, though in your home it won’t last as long, especially if its roots is confined in a pot and if they’re watered different. That’s not the plant’s fault; it’s a matter of stress and therefore the nature of keeping any cactus in a pot: It’s like a fast forward on the plant’s life cycle. It will bloom sooner, but it will have no legacy.
How do you know when it’s mature, if you’re not willing to cut the thing open? One visual clue is a corked base on the stem. Late in its life, as the columnar cactus grows taller and heavier, the lower part of the stem becomes thicker and woody, with a corky consistency (necessary to hold up weight). A smooth green base means the plant is probably still young, still in juvenile or perhaps just entering the reproductive stage of life.
The other telltale sign: arm formation. Saguaro begin to develop their first arms sometime between age of 50 and 75; before then they’re just putting all their efforts into height.
We all want our cacti to grow quickly, but in this hobby it’s seldom a virtue. A fast-growing plant generally lacks strong structure. Someone who blooms in two years probably has a different plan different than someone who doesn’t bloom until decades later. While fast bloomers are not likely to last as long as some of the desert giants, you need to consider what matters most to you. Do you want a quick pay-off at the expense of longevity? Or do you want to foster something that may outlast you?
Patience appear to be rewarded in terms of longevity. Note the first bloom year. Mark how tall the plants grow in spring to help you get to know their individual timing. Each year, take a photo of the base at the time of change. The photos, plus the notes and numbers, make a personal growth curve; a much better reference than any chart that someone else put together.
Cacti don’t produce annual wood rings, so no need to count them, like on an oak tree. Don’t assume their growth in the wild is the same as when they grow in a container, because those environments are too different. Overwatering a century-old cactus in a container can cut years off its life; keep the roots dry, but be patient.
You know what they say: Don’t judge a cactus by its age. You judge a cactus by its milestones. If you consider the one on your shelf or the tall column in your yard, how about this one? Consider the bloom. That’s a time stamp. It is a sign that the plant lived long enough to reproduce, which is what actualy counts for age.