Well, it is hard to guess, but since you generally get plentiful rainfall I expect the sweet potatoes will produce just fine. Your mix looks good in the photo. When I've grown them in containers, I got a good yield, and I used a home-made mix for them as well. I didn't want for it to be too rich because I wanted to avoid getting all foliage and no taters, and it seemed to work out that way.

Dawn, I only potted up one tub with 4 plants in it. (ornamental for Madge to play with) I liked to have never found enough dry soil to mix in. If I can get this to work I will fix up another tub, it is more work than I had expected. I only have about a dollar tied up in that tub,4 plants and the soil, so I wont lose a lot if it flops.