What does Genesis 49:22 mean?
Jacob reclines on the bed in which he will soon die (Genesis 48:1). He has called his twelve sons to his side to hear his prophecy, delivered in poetic verse, about the future of each sons' descendants (Genesis 49:1–2). Having completed his prophetic sayings about his ten older sons, Jacob now comes to his beloved Joseph (Genesis 37:3). Jacob has saved the longest and most complex blessing for the firstborn of his beloved wife Rachel (Genesis 30:22–24).He begins by describing Joseph as a fruitful bough or vine. In the case of the bough or vine, Jacob describes Joseph as being fruitful and fertile, as a well-watered tree planted by a spring with branches extending even over walls. In other words, Joseph's line would multiply and thrive. This fits with what already occurred: Jacob made Joseph into two tribes by adopting his two oldest sons—Ephraim and Manasseh—making a unique tribe of each (Genesis 48:5–6).
Some scholars note that the Hebrew terms for sons and plants are relatively distinct. They also point out that most metaphors in Jacob's prophecy involve animals. This leads towards a different metaphor, though with similar implications.