The watered White tree shoot is a quest item used in Garden of Tranquility. It is created by watering the white tree shoot (pot) with a watering can. The original white tree shoot is given by Dantaera, who says that the White tree is dying and the only way to save it is to grow a cutting from one of its branches.
After sitting for some time, the shoot will grow into the white tree sapling. It can then be transplanted into Queen Ellamaria's garden behind Varrock Palace.