Here is the list of the medals you can obtain in this garden along with a description:
Falador Sprinter: Has won a Falador knights race (can be any kind of race if organized by a Falador knight)
Falador champion: Has won a garden tournament in the name of Falador knights (can be any kind of tournament)
Falador Hero: Has done something very important for the Falador Knights, such as some kind of revolution, donation, etc.