In the play Macbeth by William Shakespeare, why does Malcolm describe his restoration of scotland a new planting?

Throughout the entire play, Shakespeare uses plant or
agricultural imagery to develop characterization and plot. If you remember, King Duncan
tells Macbeth, when he first sees him after the victorious battle, that he
has

begun to
plant [Macbeth] and will labor

To make [him] full of
growing (I. iv. 28-29)

And
when Duncan promises to do the same for Banquo, Banquo's responses is full of
agricultural imagery, for he states that

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There if I grow,

The
harvest is your own (I. iv.
31-32).

This agricultural
imagery reveals just what kind of character Duncan is; it reveals that he is a humble
and generous king, and it certainly reveals that Banquo is a most loyal servant. All
this occurs while Malcolm is listening.

So, when Malcolm
uses the analogy of the restoration of Scotland as a new planting, we not only see the
teachings of his father, but we see the new beginning for Scotland, for like a newly
planted crop, Malcolm has hopes for a bountiful harvest.