The High Hallow was a field that was beneath the snows of Mount Mindolluin yet high above the city of Minas Tirith. Standing in this spot, where only the kings of Gondor had gone, one could look over a precipice to the towers of the city far below. The High Hallow could only be reached by a steep path.
After the downfall of Sauron, Gandalf brought Aragorn to the High Hallow where the newly crowned king could view the vastness of his realm. When Aragorn remarked that the tree in the Court of the Fountain was still withered, Gandalf bade him to turn about. Opposite the precipice was a stony slope upon which one growing thing could be seen. It was a sapling of the line of Nimloth. Aragorn removed the tree and brought it to the Citadel for planting, which was the sign for Arwen to come to Gondor and be his queen.
An Inconsistency in Dates
In the text of The Return of the King it is stated: "And Aragorn planted the new tree in the court by the fountain, and swiftly and gladly it began to grow; and when the month of June entered in it was laden with blossom". The wording of this sentence suggests that Aragorn planted the sapling before June began. However, in Appendix B there is the entry: "June 25 (of 3019) King Elessar finds the sapling of the White Tree", in which case it could not have blossomed until late in the month. However, in either instance the tree was planted before Arwen arrived in Minas Tirith.