While it's a common belief, lining the bottom of your urban planter box with rocks instead of creating drainage holes is not an effective solution and can actually harm your plants. This method creates a "perched water table." Excess water drains from the soil into the rock layer but then has nowhere to escape. The soil above remains saturated, as water is held by capillary action at the boundary between the soil and rocks. This leads to waterlogged soil around your plant's roots, which is a primary cause of root rot—a condition where roots suffocate and decay due to lack of oxygen.
For healthy container gardening, proper drainage holes at the bottom of the planter are non-negotiable. They allow excess water to flow freely out of the soil. To prevent soil from washing out while maintaining drainage, cover the holes with a single layer of landscape fabric, a coffee filter, or a piece of broken pottery. The key is to use a high-quality, well-draining potting mix designed for containers. This approach ensures your plants' roots have the ideal balance of moisture and air, promoting healthy growth and preventing disease in your urban garden.