I started with a container of 150 or so red wriggler worms from a nursery almost 3 years ago. Half I put in a flower bed and started a vermicompost bin with the rest. Now I have so many I sell some once in a while to help others get started. I would ask you if the worms from Walmart were red wrigglers, and what kind of "food" do you mean? I buried rotted food with shredded newspaper, shredded cardboard, and topped the holes with rotted leaves. I continue to do this all over the yard where there are worms. I live in southern nevada and it gets pretty hot here in the summer, so I have to keep the soils wet where the worms are. Hope this helps.
Kath