Discarded big tires (tractors or semi-trucks) are free from most tire dealers. Dh cut the rums off and filled it with special dirt mixture and planted it. I will try to get pictures of it tomorrow. He started the sweet potato plants in his room from our crop the year before. He watered it faithfully all summer and could not believe what they produced. Advantage is that it is a raised bed, easier to weed, water and dig the root crop up. Older folk like us has to figure out a way to do what they used to do with less effort, so therefore we tried the free tire method. You can judge the results for yourselves.