The white rose seed are a quest item given to the player during the Garden of Tranquillity quest by Brother Althric. In order to obtain the seeds the player must throw away or destroy their ring of charos since Brother Althric believes it to be an evil device. Once disposed of, the player can simply pick seeds from the roses behind the Monastery north of Barbarian Village.
It is advisable to use the ring of charos on the well in Edgeville instead of using other methods to dispose of it. After receiving the seeds, it can be re-obtained by using a fishing rod with the well.
The rose seeds then need to be planted in Queen Ellamaria's garden behind Varrock Palace.