Absolutely, yes. It is entirely possible, and quite common, to over-water plants in an urban planter box even if it has drainage holes. While drainage holes are crucial for preventing water from pooling at the absolute bottom of the container, they are not a foolproof shield against over-watering.
The core issue is soil saturation and oxygen. When you water too frequently, the soil remains constantly wet. This saturated soil pushes out the vital air pockets that plant roots need to breathe. Drainage holes only remove *excess* water that drains down by gravity; they cannot actively dry out waterlogged soil. The result is a lack of oxygen in the root zone, leading to root rot—a condition where roots suffocate and decay, becoming unable to absorb water or nutrients. Ironically, the first symptoms of over-watering (wilting, yellowing leaves) often mimic those of under-watering.
Several factors in urban settings compound this problem. Planter boxes, especially indoors or on sheltered balconies, may have limited sunlight and air circulation, slowing evaporation. Using standard garden soil instead of a well-draining potting mix can cause compaction and poor drainage. Furthermore, the "small soil volume" in a planter box dries out and becomes waterlogged much faster than ground soil.
To prevent over-watering, focus on a proper routine. Always check the soil moisture before watering by inserting your finger about an inch deep. Water only when the top layer feels dry. Ensure you use a high-quality potting mix and containers with *multiple* adequate drainage holes. When you water, do so thoroughly until water runs freely from the bottom, then empty the saucer or cache pot underneath to prevent the plant from sitting in water. By understanding that drainage holes are just one part of the equation, you can master the balance for thriving urban greenery.