The answer to whether you should water plants until water comes out is yes, especially for container plants. This practice, often called deep watering, is the most effective way to ensure the entire root system receives moisture, not just the top layer of soil. Deep watering saturates the whole soil volume, providing the plant with a substantial reservoir of water to draw from. Overwatering is typically an issue of frequency (watering too often), not the amount given in a single session, provided the pot has drainage.
Why Deep Watering Encourages Healthy Roots
The primary physiological reason for watering until drainage occurs is to stimulate the development of a deep, robust root system. When a plant only receives small sips of water, the moisture remains concentrated in the top few inches of the soil.
This shallow watering technique trains the roots to stay near the surface, resulting in a fragile root mass that is susceptible to drying out quickly. A plant with shallow roots is less resilient and is vulnerable to stress from heat or short periods of drought. Deep watering ensures that moisture penetrates to the bottom of the pot, encouraging the roots to grow throughout the entire container volume.
A deeply rooted plant is more stable and better able to access nutrients and moisture stored lower in the soil profile. This comprehensive root development allows the plant to withstand fluctuations in temperature and moisture levels. Saturating the soil also promotes better soil structure over time, helping to break up compacted layers and improve aeration around the roots.
The Importance of Flushing Excess Minerals
Watering until the water flows freely from the drainage hole helps maintain a balanced soil environment. Both tap water and commercial fertilizers contain mineral salts. As the plant uses water and moisture evaporates from the soil surface, these non-volatile salts are left behind.
This buildup of soluble salts can create a visible white crust on the soil surface or the sides of the pot. A high concentration of these salts can interfere with the plant’s ability to absorb water through osmosis. This osmotic imbalance can lead to dehydration symptoms, such as browning leaf tips and edges.
The act of deep watering, known as leaching, forces the excess mineral salts out of the soil profile. To effectively flush the soil, it is recommended to apply a volume of water equivalent to at least twice the volume of the pot, allowing it to drain completely. This rinsing process prevents the salts from reaching toxic levels and ensures the roots can continue to function efficiently.
Exceptions to the Drainage Rule and Alternate Techniques
While the principle of full saturation is widely applicable, certain plant types and specific situations modify the drainage rule. Plants adapted to arid environments, such as succulents and cacti, prefer their soil to dry out almost completely between waterings. For these species, the goal is still to saturate the soil, but the frequency is drastically reduced.
Bottom watering is an alternate technique where the pot is placed in a tray of water to allow the soil to soak up moisture through capillary action. This method is favored for plants sensitive to water on their leaves, like African Violets, or for pots where the soil has become so dry and compacted that it repels water. Even with bottom watering, the goal remains full saturation; the plant is left to soak until the top of the soil feels moist.
The “drainage rule” is modified if a container lacks drainage holes, which is not recommended for most plants. In this case, the grower must measure and apply the volume of water necessary to saturate the soil, avoiding any excess that would collect at the bottom and suffocate the roots. For plants in pots with proper drainage, if water rushes out instantly, it may indicate hydrophobic or excessively porous soil, which requires a second, slower soak to ensure proper absorption.