I know of several people that plant at least 2-3 of each variety - about 9" apart, and then an 18" spacing between those and the next variety. It may not be the best way to plant if growing for shows, but if growing primarily for cut flowers and/or garden wow, it makes sense to me. I often only have 2-4 blooms at a time from a plant, so doubling them up should make for a more impressive display.
I plan on trying it with at least some of mine this coming year.
