Plant the potatoes

A farmer gets sent to jail, and his wife is trying to hold the farm together until her husband can get out. She's not, however, very good at farm work, so she writes a letter to him in jail: "Dear sweetheart, I want to plant the potatoes. When is the best time to do it?"
The farmer writes back: "Honey, don't go near that field. That's where all my guns are buried."
But, because he is in jail all of the farmer's mail is censored. So when the sheriff and his deputies read this, they all run out to the farm and dig up the entire potato field looking for guns. After two full days of digging, they don't find one single weapon.
The farmer then writes to his wife: "Honey, now is when you should plant the potatoes."