I'm apparently not doing something RIGHT. I've started organic sweet potatoes in large pots, using mushroom compost, as I was told to do, from my own potato starts. A great deal of greenery appeared, so I was encouraged. Waited till the greenery yellowed (three months at least it seemed) and NOTHING. No potatoes whatsoever. Only the starts. What did I do wrong? A friend suggested that I may have too much nitrogen and need a better ratio of phosphorous and potassium. Now I'm REALLY confused. Where do I GET that? How much to apply, and when? I didn't know this was going to be so difficult. So appreciate your help.Thank you!!