Absolutely, you can and often should drill additional drainage holes in urban planter boxes if needed. Proper drainage is critical for container gardening, as it prevents waterlogged soil, which is a leading cause of root rot and plant death. Many commercially available planters, especially decorative ones, may not have enough holes.
Before you start, check the material of your planter. Terracotta, ceramic, wood, and thick plastic are generally safe to drill. Use a masonry bit for clay or ceramic and a standard drill bit for wood and plastic. Always start with a small pilot hole. For plastic or fiberglass planters, place masking tape over the spot to prevent the bit from slipping.
Aim to add several holes spaced evenly across the bottom. The size should be large enough to allow water flow but not so large that soil washes out—typically 1/4 to 1/2 inch in diameter is sufficient. Remember to elevate your planter afterward with pot feet or bricks to allow free water escape.
This simple DIY modification can dramatically improve your urban garden's health, giving your plants the well-drained environment they need to thrive.