DAVE THE DIVER

First, you will need to complete the task of Khazin and his daughter (find the wedding plaque in the Rusalid archive. If anyone has forgotten where the archive is, the screenshot is below).
After that, you will need to complete a quest where the seed seller will ask you to bring him a book from the merman temple, for which you will be rewarded with seaweed seeds. You will need to take them to the merman, who is located between the Workshop and the Arcade. Before opening the farm, he will ask you to bring him a seaweed dish. Then it's up to Bancho. Get on the boat, ask Bancho to cook seaweed dishes, take them to the merman, and you will get a farm.