I had to throw my two cents in here too as I have a stone patio and love to grow things in between the cracks. The stones are in a base of sand and then I added potting soil on top of that. Kind of messy to start, but after it gets packed in and watered you can grow just about anything. My favorites are creeping thyme, alssysum and moss. You'd be surprised how little soil is required to get these things to grow. I've also found, that since it is bordered by flower beds, that every seed that falls from the beds onto the patio grows. It's kind of like a hothouse since the rocks get warmer faster than the soil. I have petunias, nicotiana, cosmos, marigold and cleomes coming up all summer long, and the really nice part is that since their root systems are so small you can water them and pull them up and transplant them. Good luck and enjoy!
Q
Walkway
Q