Joan comes to your town on Sunday mornings. You’ll have to get up early to catch her as she leaves at 12 noon. Joan offers 2 types of turnips each week: Red and white.
Red turnips
Although red turnips are a little expensive it is worth buying them whenever you can. You can buy 1 packet of seeds for 1,000 bells. You should plant them in a convenient place as soon as you can on that Sunday. You need to water the red turnip everyday or it will rot and disappear. On Saturday, you can dig it up and sell to Tom Nook for 16,000 bells.
Red turnips are also essential in the Golden Axe trading game.
White turnips
You can buy white turnips from Joan on Sunday mornings. She would normally charge between 70 and 150 bells for them.
The following section explains how to make big money from white turnips!
You will need: Money, a spare room and lots of tables. Ideally you want a low price from Joan; the lower you pay for them the greater profit you will potentially make. Turnips will rot if you leave them on the floor or in your pockets; however there is a way around this.
You will need to have enough tables in you room to fit all the white turnips you bought. Once you buy the turnips stand in front of the table and take out a fishing rod and put it on the floor. You should be standing on top of the rod now. (If you don’t stand on a rod the turnips will go straight onto the floor.) Then in your inventory click on the turnips and say 'Place in room' and they will go onto the table. Once the turnips are on the table you can leave them there free in the knowledge that they won’t spoil.
When you talk to Tom Nook you will notice an option 'Turnip prices'. Tom Nook will buy turnips for two prices each day (sparing Sunday, as that is the day Joan comes to town). One price is in the morning until 12 noon and the other price is for the rest of the day. You should try to check before and after noon everyday to get a good price; you should also check the price in other towns on your friends list if possible.
It may take 2 days or it may take 2 weeks, but eventually Tom Nook will have a price spike and will buy your turnips for up to 650 bells. In order to make a big profit it is best to hold out until he is offering over 250 bells.
Example
Joan is selling white turnips at 100 bells per turnip. If you buy 500 turnips from her:
500 × 100 = 50,000 bells
Then wait for a spike in the price at Nook's. If Nook is buying turnips for 500 bells each:
500 × 500 = 250,000
That works out as 200,000 bells!
Doing this regularly requires a large bank balance and patience to wait for a good price at Tom Nook's. This will also lower your HRA points, as your house is full of turnips for a prolonged period.