The light survey has enough north-facing entries now to say something useful, so here it is in one place.
Reliable on a north aspect above the third floor in Marrowfield: ferns of almost any kind, mint that you have accepted will be leggy, chives, parsley, and — surprisingly consistently — chard. Sixty-one members have reported chard surviving a north balcony and only four have lost it.
The failures column is longer and more useful. Tomatoes: forty-two attempts, three successes, all three on a corner balcony with west spill. Basil: do not. Lavender: do not. Rosemary: nine people have tried this every year since 2021 and I would like them to stop.