In Genesis 30, Jacob put sticks of poplar, chestnut, & almond in his sheeps' water to encourage breeding, especially of speckled sheep. Why these 3 trees?

I've heard that the Greeks associated poplar with paradise, only poplar was allowed to be burned on Zeus' altar, and the Celts associated poplar with fertility. It is mentioned in Hosea 4:13 as a favored shade tree for certain rituals. Its leaves are green on top, white beneath, presenting a high contrast, possibly related to the speckled nature of the sheep Jacob wanted.

Some cultures have associated the chestnut with enhanced male fertility and libido. It thrives in poor soil and grows quickly, so it could also be associated with heartiness.

Aaron carried a staff of almond, and it blossomed and bore fruit as proof of God's anointing (Num 17:8) and Jacob renamed the place of his stairway dream from "Almond" to "House of God".