Instructions
Visit your town between 6:00 a.m. and 12:00 p.m. on a Sunday. The clock in your town matches the internal clock on your Nintendo DS.
Find Joan in your town. Joan is a female warthog that will be walking around in a random area in your town.
Purchase red turnip seeds from Joan for 1,000 bells. You can only buy one packet per week.
Open your item menu and select the turnips to plant them.
Water the turnip every day to make it grow. If you fail to water it every day it will shrivel up and die.
Dig up the turnip when you are ready to sell it. Each day that the turnip grows it will go up in resale value. Turnips take a full week to mature completely, so if you plant on Sunday, harvest on the next Sunday.