Question
MORENO VALLEY,CA.
I am installing  some Garzanias in a 406 sq. ft.
area. How many sq. ft. does a 12x12 flat covers?
Is their a rule of thumb on how to determine a
flat of any plant sq. ft.coverage ?

Answer
Kevin,
Unfortunately there is no "rule of thumb" for planting distances because plants grow to be different widths. Gazanias don't spread out that much, so if you want them to be very close with little dirt showing, plant them between 8" and 12" apart from center to center of the plant.  If you want dirt showing in between each plant place them 18" apart on center.

All the best,
C.L.