Silver Torch Cactus Stems (Columns) Shrinking

Q. I have a clump of silver torch cactus about 7 years old and some of the columns appear to be shrinking in diameter. It appears to me that the smallest column is narrowing in diameter about 4 inches above the soil line.  The largest one also appears to be narrowing at the bottom as well. I don’t water from November through February and start watering again in March and April and September and October and fertilize twice a year with a cactus fertilizer. In the summer months of May through August I water twice a month. There are no soft spots near the ground and no pests I can see. What do you think?

Silver Torch cactus. A beautiful cactus from the high elevations of Argentinia and Bolivia.

 THEREFORE it does not like high temperatures of our Mojave Desert. Protect it from high light intensities of the late afternoon...that means dont plant it on the West or South side of a home.

A. This is a clumping cactus that grows to about four feet and can handle winter temperatures to about 20F. It also likes high intense sunlight but cooler temperatures than ours in the summer. For that reason, it performs better if it does not get intense heat during the hottest time of the day in the summer. Make sure it gets some shade if it is on the west side. Also, I would give it one more irrigation during the cooler months but your timing of irrigations look good when its hot and the soil does not stay wet. Don’t water more often than that. 

Silver torch cactus is from the dry higher elevations of Bolivia and Argentina and not from one of our deserts. It struggles during our hot summers starting in the low 100’s and particularly in hot locations (such as a western or southern exposure in full sun during June - August). It is not from the Mojave Desert! Surrounded by rock in these locations make it even hotter! So be careful when using this plant and plant it in the correct location!

Want info from Tucson on this plant?

            Many cacti have narrower stems at the bottom as they get older. Older stems get “woody” at their base and cant expand and contract as they store and use water. They also develop constrictions along the length of long stems when their growth ends. Constrictions along the stems make convenient places to propagate them. Just make sure you sanitize hand shears when cutting! If you are checked for soil drainage and root rot, then I don’t think their narrowing is a problem.