Barrel cacti have adapted to survive with little available moisture.
The barrel cactus (Ferocactus spp.) is one of several plants associated with the Sonoran and Chihuahuan deserts. Like other desert plants, the barrel cactus is well-adapted to survive over extended periods with little available moisture. This adaptation to arid conditions is reflected in the root system of the barrel cactus. Does this Spark an idea?
General Structure
Barrel cacti, as well as most opuntoids and columnar cacti, have shallow, fibrous roots that radiate horizontally from the cactus in all directions. Roots are close to the surface so that cacti can absorb water from light rains that does not deeply penetrate the soil. Barrel cactus roots may be exposed after heavy rain.
Depth
Most roots within a barrel cactus' root system are located within the upper few inches of soil, but certain species may have roots that extend up to 2 feet deep. On rare occasion, barrel cacti have been observed having a slightly longer, central main root with lateral roots designed to anchor the cactus.
Response to Water
During periods when little or no water is available for the roots to uptake, the root system has few new lateral branches or new, whitish roots that perform most of the absorption and nearly all of the root system is covered by a periderm, or flaky bark. When water is applied to these roots, root buds inside the root expand quickly to form rain roots and old roots are rehydrated, greatly increasing the plant's ability to absorb water. When the amount of available water decreases again, rain roots wither and shed and main roots return to their low-conductance state.
Transplanting
When salvaging or transplanting a barrel cactus, proper treatment of the root system is key to ensuring cactus survival. Upon digging out, barrel cactus roots can be trimmed back to about 6 inches, depending upon cactus size, and damaged roots removed just above the injury. The trimmed roots should be treated with sulfur or left in the shade for a few weeks to callous over. New roots often grow underneath the plant or directly out of cut root tips. Barrel cacti should be stored for no more than six months before transplant in a final location. The cactus roots, once transplanted, will benefit from occasional irrigation until the plant becomes established. Water the plant thoroughly about two weeks after transplant and every three weeks or so after that for about a year.
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