I’m not sure I’m extremely comfortable with my interpretations, but are you
My Prefix should come in moderation.
Thanks to @Cashbee for finding TREAT. Go upvote their answer!! :)
My Infix rule the nation.
This is a plural as alluded to by OP....and my sketchy part of the solution...by saying that MEN rule the nation? (Which isn’t entirely true.)
My Suffix communicates after germination.
This refers to an ENT (singular, because he communicates, not they communicate), because they’re talking trees from Lord of the Rings.
I suppose treatment/good treatment all around could make us better people, yes...