The test can be started at the University of Art where you learn the Formal Gardening skill (allows you to build a Formal Garden Gazebo and Formal Garden Stella) and also receive the following message (the following text from T1):
You sign up for the Test of the Formal Garden and learn to construct a Gazebo, the centerpiece of any formal garden. You also learn to build decorative Stellae, which may contain information on your plants. You are instructed that formal gardens must have between 7 and 100 flowers with a 100 foot radius. Formal gardens may be judged by any Initiate of Art and Music, and should be judged for beauty and variety of flora, not raw volume of plant matter.
Unlike other art Tests, Formal Gardens may be tended after judging has opened.
Useful links: Gazebo Locations, Painters