This is January 13th. A moment ago I read a fascinating bit of trivia that answers the question (at least for Swedes -- of which I am not one). But I still like the suggestion:
King Knut, Sweden's king from 1080 to 1086, decreed that the Christmas season should be celebrated for 20 days -- December 25 to January 13. In Sweden, it is still traditional to wait until January 13, known as St. Knut's Day, to discard the Christmas tree.
Another bit of trivia about January 13th: It is traditionally the coldest day of the year.
(Source: Ben Franklin's Almanac of Wit, Wisdom, and Practical Advice)