jacques976 when poured you will have a solid piece of concrete that will last forever the only thing is .with setting of forms ,placement of rebar and drains prep of base material.pouring concrete befor it sets you have to have a fair size crew not a job for a DIY project. block is good for small projects.
Outside The Box Landscape I just want to say that I love what you are doing. The layout is inspired and I love the concrete. Are you at liberty to tell me the particular concrete mix you are using for the walls.. I know its reinforced, but what type of cement, sand do you use and in what proportion and what is your base?. I am learning to use concrete, but its taking time. Do you know a good book?
Plant natives: Outdoor landscaping doesn't have to be labor intensive. For a no-fuss landscape, use native grasses and xeriscaping for less water usage. Save time and water with a drip system connected to your home's runoff drainage system.