Celtic tree astrology is based on the ancient idea that the time of our births is pivotal to the formation of our personality and behaviour.

 When the Druids devised their astrology charts, instead of using constellation figures like other cultures, they used trees as their symbols.  The Druids had a profound connection with trees and believed they were vessels of infinite wisdom.  They felt the entire universe existed in the form of a tree, whose roots grew deep below, representing the past, and whose trunk sat in everyday life, representing the present, and the branches reached up high into the heavens, representing the future and afterlife. 

Celtic Tree Astrology was based on the lunar calendar, so it has 13 astrological signs, rather than the 12 we know today.  The Druids designated a tree to each of the 13 moon phases in their calendar, in accordance with the trees magical properties.