Some imagine twelfth night to be the evening of the 6th January but they are mistaken, since the ancients counted from sunset not sunrise. So Christmas night was the evening of 24th December, we count the twelve days of Christmas from there.
There is a tradition that it is unlucky to keep Christmas decorations after twelfth night while others that they should stay up until Candlemas eve (1st February).
Either way don’t send your Christmas greenery for recycling – burn it! This ancient maxim was recorded in the Exeter Book in 1072,
“Holly must be burned, a dead man's legacy divided. Good fame is ever best.”
William Hone, in his Every Day Book of 1827 refers to a glossary to the Exmore dialect that has “Watsail – a drinking song on twelfth-day eve, throwing toast to the apple trees, in order to have a fruitful year, which seems to be a relic of the heathen sacrifice to Pomona.”
So sup up, by the fire and cheers!