Large Cactus Has Blown over. What to Do?

Q. I have a cactus I bought as a start from a little nursery in 29 Palms that grew a foot a year for the last 15 years. It finally tore out of the ground and fell over causing the ground to quake. It towered to 17' and was spectacular. The cactus had no water supply but was irrigated by water runoff from the roof.

 

Not this readers cactus but another cactus which is blown over because the roots have not spread out due to localized irrigation.

A. I suspect the cactus had a very small, spreading root system that finally just couldn’t support it anymore and fell over because it was top-heavy. Cacti and other desert plants have extensive, relatively shallow roots, that spread as much as eight times their height! This extensive root system provides a very efficient way of gathering sparse rainwater and provides substantial support for taller cacti.

            Non-desert plants, sometimes referred to as “mesic” trees and plants, are reported to have spreading roots as much as 2 to 3 times their height. Still quite extensive but not like desert plants. Cacti have more extensive roots that are not terribly deep for gathering sparse rainwater as quickly as possible. Desert plants convert this unexpected water into rapid growth and producing flowers. They are good at that.

Water cacti infrequently but in a large area

            So, I think it's important to periodically irrigate cacti large distances from the mother plant as they get taller. Plants get water where it’s the easiest to find it. Desert plants are opportunists. By that I mean, when water is present, they grow quickly and then shut down when water is no longer available.

            By watering these plants close to their base (e.g. rainwater from the roof) they tend to fall over as they get taller because the small size of the roots can’t support its massive top growth. Of course, I'm not mentioning how often you should water these plants. That's an entirely different topic. But when they are irrigated, water should be applied over a large area.

            I probably don't need to tell you that plant roots don't actively "seek" water, but they grow towards sources of applied water because of soil moisture. With cacti, and many of the other succulents, it doesn't take much soil moisture to get them growing in its direction.

            In my opinion, I think it's beneficial to use a hose and hose-end sprayer periodically and spray the surface of the soil around cacti to get their roots spreading outwardly and anchor them in the soil as they become larger. Of course, water should be applied at times of the year, or in intervals, that don't encourage Bermudagrass growth, a terrible scourge to landscapes.