We can add 3/4" strips of wood under any window box planter so that it will straddle your balcony railing. Balconies often have railings 4 to 5 1/2 inches wide. We can add the wood strips per your required spacing down for a snug fit. The charge is $10 regardless of the strip spacing or length of your planter. Just let us know in the comment box the spacing you'd like for the deck rail mounting wood strips and consider it done!