May is the best month to start an urban garden. The risk of frost is gone and the days grow longer, so most crops thrive.
If it's your first time, begin with low-maintenance, fast-harvest crops like lettuce, chili pepper, tomato, and basil. Lettuce lets you pick leaves about a month after sowing, and basil's lovely scent makes it especially rewarding to grow on a balcony.
Choose a pot at least 20cm deep with drainage holes. For soil, mixing commercial potting mix with leaf mold is enough.