Sure, you can give it a haircut. You could at the same time feed it a bit to encourage the next round of flowers. Happy gardening! Maureen

Thanks Maureen! I don't usually hesitate pruning annuals, but due to some unexpected financial difficulties I can't afford to replace any plants---I didn't want to lose these without first posting my question.

I think I'm a year late, but I didn't resist.
I've always used the little yellow Creeping Zinnia (Sprite Yellow Sanvitalia)for hanging baskets and those require absolutely no maintenance. I have cut them back though, put on some bloom fertilizer, and they end up great throughout the fall. (At least here in the Pacific Northwest