Praise be to Allah.
The one who planted it will have an ongoing reward from the time he planted it until the plants die. The heir will have the reward for whatever of its fruit is eaten during the time when the plants are under his care, so long as it is taken without his objection.
Whatever fruits are taken, it is better to forgive than to leave it as a debt. But if he does not forgive, then both the deceased and his heir will be rewarded for whatever is eaten, from the time the payment is due until it is finally paid. As for demanding restitution on the Day of Resurrection, priority will be given to the rights of the one from whom it was taken by force. It was said that it will be given to the final heir in the direct line of descent. This does not apply only the case of plants, but also in the case of everything that was owed and was not paid off. This ruling applies in all such cases. And Allaah knows best.