Start by checking your building’s balcony rules and talking with your neighbor. A calm conversation and a clear plan make the fix easier, especially if the drip is already causing stains or slipping hazards.
The simplest solution is a properly sized drip tray under every urban planter box. Choose a tray wider than the planter base, with raised edges and enough capacity to hold runoff from heavy watering or rain. Empty it regularly, and after storms, so it never overflows onto the neighbor’s balcony. For long boxes, use a custom tray or link several trays, and raise the planter on pot feet so you can check underneath.
If the box is built in or homemade, improve balcony planter drainage and waterproofing. Line the inside with a flexible waterproof membrane, seal seams and screw holes, and create a slight slope toward a drain outlet. Connect that outlet to a small hose or reservoir that stays inside your own space; never let it discharge over the edge. A self-watering planter with a closed reservoir is often the cleanest option because surplus water is stored instead of dripping.
Water more carefully. Use a moisture meter or lift the pot to judge weight, then water slowly and less often. Smart watering with a timer and drip line can help, but set it conservatively and check the drip tray afterward. Keep the planter away from the balcony edge so wind-driven rain and overflow fall on your side. Add a waterproof mat beneath the planter zone and extend it up the wall slightly to contain splashes.
Finally, maintain the system: clear leaves from trays, inspect seals, and check after rain. If a little water still escapes, fit a small gutter or deflector under the planter edge and lead it to a bucket. With a drip tray, waterproofing, and smarter watering, you can protect your neighbor’s balcony and keep your container garden healthy.