If these are annual dianthus it should bloom all summer if you deadhead regularly but if it were me I would spread them around your beds anyway instead of planting them enmass

Our summers get above 90 pretty often. We are very humid, too. Those are the annual dianthus, right? (Though for me, they come back.) I clip them back each time they are done blooming, and they do rebloom (I think in a month or so). The foliage gets a little ratty at times, so I then cut them back to only a few inches. They regrow and rebloom. They also need to be clipped back at times, but overall....they are tough flowers! :)

Hot and humid upstate SC here. I bought several of them last spring and they bloomed all season, with deadheading. Most of them came back this spring and are blooming again.

I too planted annuals last year, they bloomed all season (zone 6, hot and humid summers) especially when deadheaded. I cut them back to about an inch or two in the late fall, and they came back in full force, bigger and fuller, this year.