From the perspective of a Lithops, the single most critical factor in its survival is avoiding excess moisture on its above-ground body. Lithops have evolved a pair of highly specialized, succulent leaves that are designed to store water and withstand extreme aridity. The meristem tissue, the crucial growth point from which new leaves and flowers emerge, is located at the base of the fissure between these two leaves. When water is applied from the top, it can easily become trapped in this fissure and around the base of the plant. This creates a humid microclimate that is utterly foreign and dangerous to a desert dweller, leading to the rapid proliferation of fungal and bacterial pathogens. This almost invariably results in fatal rot. Bottom watering completely circumvents this threat by allowing the plant to draw water only through its root system, keeping its vulnerable body perfectly dry.
A Lithops possesses a long taproot accompanied by a network of finer secondary roots. This root system is designed to seek out deep, residual moisture in the soil after a rare rainfall. The plant's health is directly tied to the vigor and reach of these roots. Top watering often only moistens the upper layer of the soil medium, encouraging roots to grow sideways and upwards to access this easy water. This results in a shallow, underdeveloped root system. Conversely, bottom watering mimics the natural conditions the root system is adapted for. As the water is drawn up from the bottom of the pot, the entire soil column becomes evenly moist. The taproot is encouraged to grow deep and strong to access this water source, and the secondary roots spread throughout the pot. This creates a more resilient, efficient, and healthier plant that is better at nutrient uptake and more resistant to drought stress.
Lithops have a strict and complex annual growth cycle that includes a dormant period, typically during the hottest summer months and sometimes in the coldest part of winter. During dormancy, the plant's metabolic processes slow dramatically, and it should remain completely dry to prevent it from breaking dormancy incorrectly or attempting to grow when it should be resting. Top watering makes it difficult to control moisture levels at the very bottom of the pot where the taproot resides, risking a slight dampness that can trick the plant into activity. Bottom watering provides a clear and unambiguous signal. The plant is only hydrated when the pot is placed in water, and the duration can be precisely controlled to achieve a thorough but not excessive wetting. This method supports the natural boom-and-bust cycle of hydration that Lithops expect: a deep, thorough drink followed by a long, complete period of dryness.
The fast-draining, gritty, mineral-based soil that Lithops require is designed to not hold onto water or nutrients for long. Top watering, especially with tap water that may contain dissolved minerals, can lead to a gradual accumulation of salts and minerals on the soil surface and around the plant's body. This crust can potentially alter soil pH and, in extreme cases, cause chemical burns to the delicate tissue of the plant. Bottom watering helps to flush these salts downward and out of the pot with each watering cycle. As water is absorbed from the bottom and evaporates from the top, it creates a slight upward capillary action that can help draw excess salts away from the root zone and toward the surface, where they can be carefully removed if they form a visible crust.
