I usually grow A. konjac in ground but a few potted as well. In addition to time release in your mix they respond well to frequent balanced water soluble fertilizer like MG. Once it's leafed out full strength once every week or two should be fine. Bone meal or similar in the potting mix will help too. I expect a doubling in tuber diameter every year.
Regular, even premium, potting soil may not drain well enough for an Amorph. I've used a 1/1 potting soil/Perlite mix or lately potting soil/Perlite/pine bark fines(or shredded).
