Sekiro:Shadows die twice-A small in-game question (Sekiro: Shadows Die Twice)

In short, after the battle with Gyobu Oniwa, he explored the location, found a merchant, sold a pumpkin seed. I bought it, then ran a little, came back again, he sells it again. Hence the question: the potion of healing can be stacked indefinitely or what? Or is there a limit. Depending on the answer, tell me if it is worth buying more seeds.