My coreopsis zagreb blooms later than some here close to the ocean and I don't reliably get rebloom - so I don't deadhead. The deer have been keeping it 'clipped back' for me this year so a mute question anyway ................😊 It's the first time in 10 years they've noticed or wanted it. (I prefer the soft yellow of moonbeam but the zagreb seems to be a tougher plant overall - mine takes a little abuse becoming dry in my circular driveway island bed) I do cut it back hard in late fall to tidy up that area of bed.

I cut lobelia cardinalis back just a little harder than deadheading and will sometimes get sporadic rebloom on fresh growth. Nothing as showy as first bloom but again, we're not as warm or bright here so coastal.