From a Correspondent:
We have four golden barrel cacti in our yard. Two of them have started growing mini cacti on them. One of them has at least 30-40 growing on it. This cactus suddenly turned rotten on the crown. Three questions: 1. Are the mini cactus growing on the main plant normal? 2. If they're normal, any idea why the crown rotted? My wife thinks the excessive growths "sucked" the life out of the cactus. We only water the cacti once or twice a month. 3. What do we do?
C., in Gilbert, Ariz.
Congratulations: you are witnessing one of the coolest events of the desert garden. Golden barrels (Echinocactus grusonii), are normally solitary, but when the terminal bud (the growing point in the center) is damaged, the plant responds by producing the offsets that you're now seeing. It's a reproductive strategy to ensure the survival of the plant.
Not to worry: the main cactus didn't get killed by the offsets; the offsets formed because of damage to the main cactus. It's hard to say of course, what might have caused the damage. It really doesn't take too much. I know of nursery professionals who initiate offset growth by bouncing the eraser end of a pencil on the growing point. Depending where on the main cactus the offsets are growing, they may well continue to grow even after the main stem has rotted out beneath them. If it appears that they are wholly surrounded by rotting tissue, you may want to try twisting off a few of them and seeing if you can root them independently. But, in the spirit of discovery, if I were you I would let it go and see what happens.
As to the water, it partly depends on your drainage and their sun exposure. Golden Barrel in well-drained soil in full sun will need good water, but if your soil is at all clay or if they are in shade or part shade, you might try backing off the water just a bit, and see how they do then. If your other two Golden Barrel are doing well, though, chances are your watering schedule is fine. Just be sure you don't water so much that you rot the roots, or so little that the plant shrivels and turns yellow.
Remember, for all desert plants, water should be deep, but infrequent.
I hope this helps,