the Eve of Epiphany (Twelfth Day of Christmas) - January 5 - 6

from Writer's Almanac (American Public Media: Garrison Keillor):

Today (Saturday, Jan. 5, 2012) is Twelfth Night. It's the eve of Epiphany, the official end of the Christmas holiday season, and the day on which many people take down their Christmas decorations or risk bad luck for the coming year.

Poet Robert Herrick wrote: "Down with the rosemary, and so / Down with the bays and mistletoe; / Down with the holly, ivy, all, / Wherewith ye dress'd the Christmas Hall." It's a last Yuletide hurrah before everyone returns to the mundane workaday world of the rest of the year. Though the origin of the celebration dates back to the Roman Saturnalia, most of the traditional observances of the holiday that have survived date back to medieval England. It was the end of a holiday season that began with All Hallows Eve and, in some cultures, it also marks the beginning of the Carnival season.
It's a Twelfth Night tradition to choose a king and queen for the festivities. Usually, this involves beans and baked goods. In English celebrations, a plum cake is baked with a bean and a pea inside. If a man finds the bean, he is crowned the Twelfth Night King, also known as the Lord of Misrule. The woman who finds the pea is crowned Queen. But if a woman finds the bean instead of the pea, she chooses her own king.
Part of the Twelfth Night tradition involves pranks, role reversals, and general chaos. Servants dressed as masters, men dressed as women, and people roamed the streets in gangs, decked out in costumes and blackened faces. Shakespeare's play Twelfth Night features many of the traditional elements of the holiday.

In some parts of England, Twelfth Night was also traditionally associated with apples and apple trees. People would troop out to their fruit orchards bearing a hot, spiced mixture of cider and ale for the "wassailing of the trees." They would pour the wassail on the ground over the trees' roots, and sing songs, and drink toasts to the health of their orchards. They also hung bits of cider-soaked toast in the trees to feed the birds. The attention paid to the orchards during the wassailing would be repaid with a bountiful harvest the following fall.

English settlers in the Colonies brought the Twelfth Night tradition with them. In colonial Virginia, it was customary to hold a large and elegant ball. Revelers chose a king and queen using the customary cake method; it was the king's duty to host the next year's Twelfth Night ball, and the queen was given the honor of baking the next year's cake. George and Martha Washington didn't usually do much for Christmas except attend church, but they often hosted elaborate Twelfth Night celebrations. It was also their anniversary; they'd been married on January 5, 1759. Martha Washington left behind her recipe for an enormous Twelfth Night cake among her papers at Mount Vernon. The recipe called for 40 eggs, four pounds of sugar, and five pounds of dried fruit. It wasn't until the mid-1800s that Christmas became the primary holiday of the season in America, and at that point, Twelfth Night celebrations all but disappeared.