Cactus are succulent plants, almost all of which live in desert climates. The number
one cause of death in cacti is overwatering! How do you determine when to water?
The usual method of feeling the soil just won't work; you would have to be able to
feel the middle of the rootball, plus you don't want to disturb the surface roots. (The
number two cause of cactus loss is fungus; disturbing the roots causes cracks, which
is the entry point for the infection.)