Basal rot of prickly pear and other cactus species usually develops near the soil line. Symptoms may include a discoloration of tissue, (yellowing or browning), a water-soaked rot, and eventual collapse of the entire plant.
Although fungi can contribute to the rotting of plant tissue, the primary problem is often a growing medium that remains too wet. The cactus soil mixes sold in stores are appropriate for species such as Christmas or Thanksgiving cactus, but need to be amended with additional sand for species such as prickly pear. Adequate drainage holes are also needed to allow excess water to flow out of the pot. Placing the pot on a layer of gravel or rocks and then on a saucer is helpful.
Finally, water conservatively. Prickly pear is native to northern Mexico and the southwestern United States and can tolerate dryness
This article originally appeared in the December 13, 1996 issue, p. 176.