King, a Scotland Under-19 international, was rewarded with a three-year professional contract last summer after impressing for the reserves.
He came through the ranks at the Walkers Stadium along with the likes of Max Gradel, Andy King, Joe Mattock and Luke O'Neill and can play in midfield or as a striker.
King is set to make his debut for Trewick's side in Saturday's clash with Accrington.
Meanwhile, Peterborough defender Blanchett has also joined the Bulls on loan for a month.
He last featured for Posh in February, coincidentally at Hereford, and will go straight into the Bulls squad to face Stanley.