Just remember that sweet potatoes don't need much in the way of fertilizer, particularly nitrogen. If you over-fertilize, the sweet potatoes will have gorgeous leaves, and lots of them, but won't make much in the way of tubers. I fertilize mine when they are planted with a vegetable fertilizer, something like 4-8-6 but grow them in a mix of 1/2 Black Kow, 1/2 milled sphagnum moss, and add 1 cup of coarse perlite per 2-3 gallons of mix. This gives a very lite, well-draining mix and the Black Kow, being 1-1-1 minimally fertilizes all summer long. I don't supplement with any additional fertilizer.
