I don't...I want flowers as soon as possible, and soon that first flower will be dead headed....and there's your pinch.
If you pinch your plants will get fuller faster, but you will delay bloom by about 2 weeks.
I think by mid July you will not know if you pinched or not....all will be the same.
Linda C

Shapiro,

Benary's Giants are bred to be cut flowers and the central main flower is kept for that purpose. If your main purpose is for landscaping rather than cutting, then pinching out the central shoot can be a good idea. As an amateur zinnia breeder, I am impatient to see what the flower is going to look like, so I don't pinch. Some varieties of zinnias are naturally branching and do so without the persuasion of pinching. One recent specimen in my breeding program is this "marigold flowered" zinnia, which began branching all on it own early in its development.

MM
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Dear LindaC and Maineman: Thank you both for your excellent advice!