Absolutely, it is very possible to over-water plants in an urban planter box, even one with drainage holes. While drainage holes are essential for preventing water from pooling at the bottom, they are not a foolproof guarantee against over-watering. The primary risk comes from watering too frequently, which keeps the soil constantly saturated. This deprives plant roots of oxygen, creating an environment where harmful fungi thrive, leading to root rot—a common and often fatal condition for plants.
Signs of over-watering include consistently wet soil, yellowing leaves, wilting despite moist soil, and a foul smell from the soil. To avoid this, always check the soil moisture before watering. Insert your finger about an inch or two deep; if it feels damp, wait. Ensure your planter box has adequate, unobstructed drainage holes and uses a well-draining potting mix. Adjust your watering schedule based on factors like plant type, season, sunlight, and box size. In urban settings, wind and heat can dry boxes quickly, but the principle remains: water deeply only when needed, allowing the soil to partially dry out between sessions.