While I agree with all of the above, I think to address your initial concern you should at least try to dig down in a select spot just to see if there is a floor or if that clay you spoke of has been hard packed to act as one. In my experience most of the problems friends and acquaintances ask me about are due to material, such as scrap brick, extra concrete and even insulation dumped and buried during the build. Plants initially take off then weaken and die.
I can understand the feeling of exasperation and the prospective exhaustion of having ANOTHER garden duty, but, a compost pile can be built and ignored for a long time and the end product would be a boon. But in any case its good to be out and active, bringing life to an area that had none! Kudos!
