The appointment follows the retirement of David Singleton, who was a member of the Barenbrug team for over 13 years.
Horner joined Barenbrug at the beginning of 2015 and is responsible for the entire south west region.
He was at Tewkesbury Park for fourteen years, before taking up the role of course and estates manager at Gloucester Golf Club, where he spent the next seven years.
Barenbrug managing director Paul Johnson said: "Sam will be a great asset to the team as we build upon our presence in the South West. His knowledge, reputation and 20 years’ experience within the industry are an impressive mix, which will add significant value for existing and future customers.
"As with all our technical sales team, we are here to provide advice, guidance and reassurance to the turf industry. We are looking forward to working with Sam and better understanding the needs and requirements of our south west customers."