For decades, gardeners have faithfully added a layer of gravel or stones to the bottom of planter boxes, believing it improves drainage. However, modern horticultural science reveals this common practice is actually counterproductive. When you place gravel beneath soil in a container, you create what's known as a "perched water table" - the water doesn't freely drain from the soil into the gravel layer as intended. Instead, soil particles hold moisture at their bottom interface with the gravel, keeping roots in a consistently wet environment that can lead to root rot.
The key to proper drainage in urban planter boxes lies not in adding gravel, but in using the right soil composition throughout the entire container. A well-draining potting mix containing materials like perlite, vermiculite, or coarse sand allows water to flow evenly while retaining appropriate moisture. For optimal plant health, ensure your planter has adequate drainage holes at the bottom rather than relying on gravel layers. These holes, combined with quality potting soil, provide the drainage and aeration that plant roots truly need to thrive in urban environments.
Urban gardeners can achieve better results by focusing on soil quality and container design rather than traditional gravel layers. This approach not only supports healthier plants but also reduces the unnecessary weight that gravel adds to elevated planters and rooftop gardens.