Answer: Knowing if, when, and how much to water cacti and other succulents can be one of the most difficult aspects of growing them successfully. Simply put, they are not like other plants when it comes to their water needs. More cacti die from overwatering than from droughty conditions.
Cacti, agaves, aloes, sedums and other succulents have special abilities when it comes to storing and utilizing water. To one degree or another, they all have thick, fleshy, water-storing leaves and, or stems. They also have exceptional methods to limit their water consumption. Surfaces exposed to the drying effects of sun and wind are small in proportion to their total mass. This is especially evident in plants like saguaro and barrel cacti. Thick waxy cuticle layers on outer surfaces help seal in moisture. And a smaller than normal number of pore openings in leaves and stems further restrict moisture loss.
As a general rule, established native cacti and other succulents will benefit from twice-monthly waterings when temperatures are consistently above 90 degrees.
When cactus are not getting enough water, their outer skin begins to wrinkle. This is caused by the shrinkage of water-storing tissues in the plant. If this happens, water deeply and the plant will revive.
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