Horst played highschool ball at Des Lacs-Burlington High School in Des Lacs, North Dakota where they took second in state his senior year, behind Horst's pitching. That same year he was named Mr. Baseball in North Dakota. He also played Legion baseball for the Burlington Bulldogs.
Playing career
Cincinnati Reds
Horst started his professional career in 2007. He played one game for the Gulf Coast League Reds and 16 for rookie-class Billings in '07, going a combined 3–2 with a 3.24 ERA in 17 relief appearances.
He played 2008 for the single-A Dayton Dragons, starting 10 games and appearing in 36 total. He went 8–2 with a 2.38 ERA. He started all of his games in 2009. In 23 starts for the single-A advanced Sarasota Reds, he went 6–13 with a 3.25 ERA; in 5 starts for double-A Carolina, he went 1–4 with a 6.21 ERA.