In response to the story UNC cuts Christmas trees from its libraries I was asked for my opinion about whether there is any legal problem with a library at a public university displaying a Christmas/holiday tree.
My answer was: “No, not as long as I don’t have to either put it up or take it down, or it doesn’t have religious ornaments on it.”
Strictly speaking, a tree with colorful lights, tinsel and beautiful ornaments can be legally put up in a public building any time of the year, including December. To this extent, it’s not a separation of church and state issue.
But if there is anything else on the tree or underneath it of a religious nature, then my answer is: “It all depends.”
There have been three Supreme Court decisions which collectively hold that (1) government cannot erect a display that endorses a particular religion and (2) if government permits a private party to put up a religious holiday display, it must let persons of different faiths or no faiths to put up holiday displays. (NOTE: a permit may be required and reasonable rules governing time, place and manner are permissible.)