I live on the top floor of an apartment building in a southern european city where there is a small terrace with some plants on it.
I've been growing plants from seeds I collect from the wild for a few years now. I start them in 6" / 15cm plastic pots and then move up. I'm not a very good gardener and it's a hit and miss affair. Some plants don't survive our ferocious hot summers either because I haven't noticed it's dripper is blocked or some other reason - I have actually managed to drown an olive tree when I didn't notice its bung hole was blocked.
Most of my plants are now over 10 years old and in very large clay flower pots. I repot them every 3 to 4 years. I have some coming on including jacaranda, mediterranean pine, cork oak and holm oak. And what I think is a Chinese Elm that seeded itself in a pot that contained an amaryllis - this, I have decided is going to be my first bonsai.