Best Time to Plant

A prisoner in jail receives a letter from his wife: “Dear Husband, I have decided to plant some lettuce in the back garden. When is the best time to plant them?”
The prisoner, knowing that the prison guards read all mail, replied in a letter: “Dear Wife, whatever you do, do not touch the back garden. That is where I hid all the money.”
A week or so later, he received another letter from his wife: “Dear Husband, you wouldn’t believe what happened. Some men came with shovels to the house, and dug up all of the back garden.”
The prisoner wrote another letter back: “Dear wife, now is the best time to plant the lettuce.”