Reversing Desiccation in Pot-Bound Barrel Cacti

Three large barrel cacti, 2 years indoors, yellowed/shriveled from base up—one dead, two declining. Not overwatered; recently repotted from nearly soilless pots. Likely chronic underwatering + pot-binding: water couldn't penetrate root mass, nutrients depleted. Repotting was correct. Now: water tiny amounts frequently, gradually increasing over weeks as new roots form. Too much too soon causes rot. Hot temps accelerate desiccation. Dormancy from drought mimics winter shutdown. Repot annually/biennially. Water by soil feel, not schedule. More light/heat = more water. Gradual rehydration is the only way back.