Hi all, I'd appreciate your advice. I live in a small co-op apartment building in New York City, and our back yard is sad, barren concrete. I'd like to build two largish raised beds out of interlocking concrete blocks (decorative, not plain concrete) to hold small trees, bushes, flowers--looking for low-maintenance perennial landscaping here, not a veggie garden. I'm thinking of 12' long x 4' deep x 3' tall. Here are my questions for you wise people:

1) Drainage: Since it will sit directly on concrete, how should I allow for good drainage? I'm thinking of using a layer of crushed stone at the bottom. Is there anything wrong with getting free crushed stone on Craigslist? Should I top that with sand? With large bark chips?

2) Lining: Do I need to line the whole thing with fabric? If so, should I lay the layer of crushed stone (or whatever), then install the fabric?

3) Soil: Can I get free/cheap topsoil fill dirt and amend it liberally with compost and/or peat moss? Or do I have to buy bagged soil? Any suggestions, keeping in mind that I'm worried about drainage?

4) Back wall: The beds will back up to an existing old mortared stone retaining wall. Should I do anything to protect that wall, like use liner fabric? Or just not worry about it?

5) Plants: Any fun ideas on plants I should choose, especially bushes or small trees, that will fill out but not require too much root space?

Thank you so much for any thoughts you have at all!