Congratulations on a fine and worthwhile project. I once took part in a similar exercise. The group filled a crate with some very good topsoil and planted some watermelon seeds in it. When they were well established, we left about four of the best plants and discarded the rest. We then took it to the very top of a very large heap of quarry stones. We dug out a space and placed the crate in it. We covered it lightly with stones and left everything to the weather. Within a week the vines had grown out and a few weeks later, the pile was covered by the vines laden with watermelons. Many people were quite mystified as to how those vines got there. Of course none of them went up to the top to see; they were only there for the watermelons.