Knight, who drives in the Mini 7 Championship, has a degree in industrial design and technology as well as a Writtle College diploma in garden design.
He said: "You don't just have to use wooden fencing in a garden. I understand materials because I have trained in them. I get engineering because I have raced cars. People don't use materials such as carbon fibre and Kevlar in gardens."
Knight, who works for Patricia Fox's Aralia Garden Design, secured the title with Brownfield Beauty, inspired by industrial architecture on brownfield sites. Runners-up were Katherine Wills and Andrew Percival.