Assuming you are in the Northern Hemisphere, a north-facing balcony is usually a shady spot, but it is rarely completely dark. Most north-facing balconies get soft, indirect light, reflected light from walls and windows, and sometimes a little morning or late-afternoon sun. That makes an urban planter box on a north-facing balcony best suited to shade-tolerant, compact plants that prefer steady moisture and protection from harsh afternoon sun. In a planter box, choose shallow-rooted plants and make sure the container has drainage; a depth of about 25–30 cm is enough for leafy greens and herbs, while small ferns and dwarf hostas do better in a deeper box.
The most reliable edibles are leafy greens. Loose-leaf lettuce, spinach, arugula, kale, and Swiss chard generally grow well in partial shade, especially in spring and autumn. In summer, shade can actually help lettuce and spinach avoid bolting too quickly. Harvest outer leaves regularly to keep plants productive. For herbs, mint, chives, parsley, cilantro, lemon balm, and chervil are good choices for a north-facing planter box. Mint is vigorous, so keep it in its own pot or a lined compartment. Avoid sun-loving herbs such as basil, rosemary, lavender, thyme, and oregano if the balcony is truly north-facing; they usually need much more direct sun. Scallions and radishes can be tried, but expect slower growth and smaller roots.
For flowers and foliage, impatiens, wax begonias, fuchsia, wishbone flower, and pansies or violas in cool seasons can thrive in bright shade. Dwarf hostas, heuchera, and small ferns add texture and structure. If the balcony is in deep shade, focus on ferns, hostas, heuchera, and mint. If it gets a little sun, add lettuce, parsley, and pansies. Use light-colored containers to reflect light, choose a quality potting mix with good drainage, water less often than you would on a sunny balcony but check moisture regularly, feed lightly, and protect tender plants from wind. With the right shade-tolerant choices, an urban planter box on a north-facing balcony can be productive and attractive rather than a struggling collection of sun-loving plants.