My neighbour in the flat below mine grows tomatoes in a washing-up bowl on his balcony. It is, by any horticultural standard, a terrible growing setup - too shallow, too hot, not enough root space. The tomatoes he gets are small, irregular, and about four weeks later than they should be. He talks about them with the enthusiasm of someone who has just discovered the wheel.
He is doing it exactly right.
What gardening actually is
There is a version of gardening that requires space and time and soil. That version is real and it is wonderful, and it is also not available to most of the people I know. What is available - to almost everyone - is the version my neighbour is doing: something alive, something you are responsible for, something that requires you to notice things.
The noticing is the point. Gardening trains a kind of attention that is different from any other kind. You can read about why a plant's leaves are yellowing and learn something general. When it is your plant, on your windowsill, you will learn something specific - and you will remember it, because you were paying the particular kind of attention that comes from caring about an outcome.
What grows well in the conditions most of us have
Most urban growing situations share a few characteristics: limited direct light, temperature fluctuations, small containers, inconsistent watering (because life). The plants that do well in these conditions are not always the plants that get the most column inches.
Herbs, obviously - but not all herbs equally. Mint and chives are almost unkillable and will forgive a week of neglect. Basil is not; it needs heat and consistent moisture and will punish you for a weekend away. Rosemary is somewhere in between and smells remarkable.
For something that actually grows rather than survives, consider cut-and-come-again salad leaves in a window box. A south-facing sill gives you two cuts a week through spring and early summer. Cherry tomatoes in the largest container you can manage (at least 30cm deep) will produce from July onwards on a sunny balcony. And if you want something that will genuinely astonish you, try a courgette in a grow bag. They look enormous for an apartment growing situation, they produce prolifically, and the flowers are edible.
The politics of urban growing
There is something worth saying about why this matters beyond the personal. Urban green space is distributed very unequally. Access to gardens is a class marker in most cities - the further out, or up, you go, the less you have. Growing on balconies and window ledges and in shared hallways is not a solution to this inequality, but it is a refusal to simply accept it.
My neighbour with the tomato bowl has been growing on that balcony for six years. He has extended his setup now - three containers, a grow bag, a vertical planter attached to the balcony rail. He knows things about the microclimate of that corner of the building that no one else knows. That knowledge is his, and it is worth something.