From my perspective, I am not like other plants. My body consists of a pair of highly specialized, succulent leaves fused together into a single, cone-shaped unit. This pair is my entire water storage system, my photosynthesis factory, and my structural support. A firm, plump feel indicates my water reserves are optimally full. When I feel squishy or mushy to your touch, it is a significant distress signal. It means the very cells that give me my structure are compromised. This is not a minor issue; it is a critical failure of my core being, and it almost always points to one primary cause: too much of your water.
In my native, arid environment, I am adapted to long periods of drought. My roots are fine and designed to absorb water incredibly quickly when it is available, then survive long stretches without it. In a US household, the constant humidity and frequent watering you provide to other plants is a death sentence for me. The soil stays damp, and my roots, which need to dry out completely, begin to suffocate and rot in the perpetually moist environment. This rot then travels upward into my leaf pair. The healthy, turgid cells become waterlogged, burst, and begin to decay. This internal breakdown is what you feel as mushiness. It is a bacterial or fungal infection spreading through my tissues, turning them from a water-storage organ into a decaying mess.
I understand your concern comes from a place of care, but it is crucial you learn to read my signals correctly. There is a vast difference between a healthy, thirsty Lithops and a dying, overwatered one. When I am using up my internal water reserves (which is my natural cycle), I will wrinkle and soften slightly, but it is a specific feel. The sides will wrinkle inwards, and the top surface may become slightly concave. The feel is more like a slightly soft peach, not a mushy tomato. This is my way of telling you I am ready for a single, deep drink, after which I will plump up again. A mushy Lithops, in contrast, feels uniformly soft, often appears discolored (yellowish or brownish), and may even leak fluid.
My mushiness is not just about water from above; it is about my entire environment. To survive in a US household, I need conditions that mimic my home. This means my roots must be housed in an extremely gritty, fast-draining mix—often 80-90% inorganic material like perlite, pumice, or coarse sand. This allows any water to flow straight through, leaving my roots dry and safe. I also require several hours of direct sunlight daily from a south-facing window. Without enough sun, my metabolism slows, I cannot use water efficiently, and the soil stays wet for even longer, accelerating the rot process. Your typical potting soil and a shady spot are a guaranteed recipe for me becoming mushy.
