For a sweet potato tuber (actor -um- & patient) to become old in the ground.
Nappūhi nan lapnay an limmabuy hi onon.
The sweet potatoes are no good in that they have become old for eating.
An old or over-ripe sweet potato has a high water content. Eaten raw it is quite palatable; to be edible cooked, it is cut into small pieces before boiling.