"I have begun to plant thee [Macbeth], and will labour to make thee full of growing. Noble Banquo / That hast no less deserved, let me infold thee / And hold thee to my heart" (1:4)
The notion that men could be planted and allowed to flourish is an ancient concept that can be found repeatedly in the Old Testament.
In Jeremiah 12:2, it states that Jehovah "Thou hast planted them, yea, they have taken root: they grow, yea, they bring forth fruit: thou art near in their mouth, and far from their reins"
King Duncan is responsible for doing the planting of both Macbeth and Banquo; both burst forth in very different ways: Macbeth, shortly after this scene, plots to kill Duncan, therefore destroying his roots.