Saguaro Cactus...100 yrs.to grow one arm???

[Mott_the_Hoople]

On a recent trip to Arizona, another occupant of the vehicle pointed out that this
Cactus needs 100 yrs to grow an arm,so for the next 100 miles we all looking at
cactus arms. There were alot of Cactus without Horizontal appendages. We
surmized they were 90 yrs. old.

Another interesting point this person pointed out on the return trip to California.
These Saguaro Cactus do not cross the Colorado River to grow in California.
Like a legion of Soldiers that were defeated at rivers edge, we did not see one
in California. How can millions of Cactus Grow accross Arizona and suddenly stop
at the river. Are there no Sugauro’s in Caifornia???

[Q.E.D]

Why do saguaros grow arms?
So they can wave. Okay, not really - just a little cactus humor! As a saguaro reaches maturity, arms emerge where the trunk is the thickest. This branching allows for more water storage as well as prolific fruiting, and consequently helps ensure future generations of saguaros. Not to outdo the main stalk, the arms also have a very slow growth rate. Measurements made on saguaro arms at Saguaro National Monument East near Tucson recorded growth rates of approximately two to three inches per year. The number of arms grown varies from cactus to cactus - one saguaro in the Saguaro National Monument East, affectionately known as “Grandaddy,” grew fifty arms over its lifetime!

From here.

[Darwin_s_Finch]

According to this site, Saguaros begin growing arms at around 65 to 75 years old. However, at around 125 years, a Saguaro is considered “mature”, and as you can see from the images, will already have several arms, indicating that they don’t need 100 years to grow.

Also, this .pdf document has some info (and a map) of the range of the Saguaro cactus (Carnegiea gigantea). It does show up in the extreme southeast of California, and its range is limited by frost and elevation; it’s quite temperature sensitive. That document also mentions that in areas of lower precipitation, it can take up to 100 years before arms appear, but the arms still probably grow more than one arm every 100 years.

[Bad_Samaritan]

As one having several saguaros in their yard, I can weigh in a bit with personal experience here. I have heard 50-75 years from various sources for arms to appear on a saguaro in a natural environment. I don’t dispute this or any other previously noted cites. But in an (artificial) residential enviroment, where abundant water & higher humidity are present, they can & often do grow faster and yield arms earlier in their life cyle. I have a 16 ft. saguaro in my front yard that I know is 24 years old and it has 5 small arms already. The arms have experienced about 1-2" annual growth rates since appearing about 5 years ago.

As previous poster noted, their range is limited by temp & elevation, but also by water availability. Travelling west to California, the Sonoran desert becomes more arid, eventually giving way to the very dry Mohave desert of SoCal. essentially near the Colorado river. Saguaros are thirsty buggers, and will grow a tremendous water collecting root system to a nearby water source, as evidenced by the large tree-like roots extending 25 feet or more from one of my saguaros to a neighbor’s heavily watered fruit tree.