mine get more blooms when I pinch,than when I don't.When it has 4 leafs when its starting to sprout up the next set.I pinch.It might also depend which kind.I've grown the gems,safari,some other 2 tone like safari and the common yellow gets about 1 1 1/2ft.never tried the tall ones.They are one of the easiest plants to grow from seed.
I've never pinched back my marigolds and they always to fill out and get bushy on their own. However, I do deadhead them (pinch off the spent flowers) so they will produce more blooms and it keeps them neater looking.
Marigolds.......are the easiest things to grow.. They do bushy alone,,, and they are great to plant among your vegetables to keep the bugs and pests off........The pests dont like the smell of marigolds. I planted dwarf french and cracker jack talls this time, from seed..My CJ are really nice I will take a photo.