The sight of liquid droplets forming along the tips or edges of calla lily leaves, often mistaken for dew or a sign of overwatering, is a fascinating display of plant physiology called guttation. This is a normal, natural process used by many plant species, including calla lilies (Zantedeschia genus), to manage internal water balance. Observing these “tears” is not an indication of a problem, but rather how the plant regulates its hydration.
The Scientific Process of Guttation
Guttation is powered by a mechanism known as root pressure, which drives water upward through the plant’s vascular system. During the day, plants typically lose water vapor through open pores called stomata in a process called transpiration. However, at night, most plants close their stomata to conserve moisture, which effectively stops transpiration. When the roots continue to absorb water and minerals from the soil even after transpiration has ceased, a positive hydrostatic pressure begins to build up inside the plant’s xylem vessels.
This resulting root pressure forces the water, which is now a dilute solution known as xylem sap, to move up the stem and into the leaves. The excess liquid must be expelled to relieve this internal pressure. The exit points for this liquid are specialized structures called hydathodes, which are distinct from the stomata used for transpiration. These hydathodes are permanently open pores typically located along the margins or at the tips of the leaves, acting as a pressure-release valve for the saturated plant.
Guttation is fundamentally different from dew, which is formed by the condensation of atmospheric moisture onto a cold surface. The liquid droplets from guttation originate from inside the plant and are actively exuded under pressure. This process is restricted to certain vascular plants that can generate sufficient root pressure to push the fluid out.
Environmental Conditions That Trigger Dripping
The occurrence of guttation is directly tied to a specific combination of environmental factors that collectively suppress the normal water-loss process of transpiration. The two primary conditions required are a high level of soil moisture and high atmospheric humidity. When the soil is saturated, water is readily available for the roots to absorb, leading to maximum water uptake and the subsequent buildup of root pressure.
Simultaneously, high humidity in the air prevents water from evaporating easily from the leaf surfaces. The air is already saturated, meaning the plant cannot effectively release water vapor through transpiration. This combination—high water input from the roots and low water output from the leaves—creates the pressure imbalance that necessitates guttation.
For these reasons, the dripping is most frequently observed at night or during the cool, still hours of the early morning. The cooler temperatures, lack of sunlight, and stagnant air all contribute to an environment where transpiration is minimal.
Understanding the Liquid and Plant Health
The droplets exuded from the calla lily are not pure water, but rather xylem sap, which is a dilute solution of various substances absorbed from the soil. This liquid contains inorganic mineral salts, sugars, and sometimes amino acids. The dissolved solids in the sap typically constitute between 0.05 and 0.5 percent of the total liquid volume.
For the calla lily, guttation is generally a positive sign indicating a healthy, well-hydrated, and actively absorbing root system. The plant is effectively managing its water flow and maintaining turgor pressure.
If the plant has recently been heavily fertilized, the exuded liquid will contain a higher concentration of salts. When the guttation fluid evaporates, it leaves behind a residue of the dissolved minerals on the leaf surface. This residue can sometimes leave a noticeable white, crusty deposit or cause slight leaf tip burn if the salt concentration is excessive. In such cases, occasionally wiping the leaves with a damp cloth can prevent mineral buildup and maintain the plant’s aesthetic appearance.