There doesn’t seem to be any root rot, all of the roots are a healthy white?
Sometimes, even if the roots are perfectly white, there can still be a fungal infection present.
This can be due to wet soil, or soil that never has a chance to dry out, completely, down to at least 2 or 3 inches. This can be taken care of with a fungicide. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
My dianthus plugs are about 5 inches tall. I am repoting them. Should I pinch out the tops for a fuller plant?
Pinching them will be OK, but leave them intact. Just pinch until you feel it give. This way, you have the original top, and a more full canopy.
https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
k? I heard you can cut them back . Can I do it with a scissor? Just dead head or much lower? And how long will it take to bloom again. I live in NH, in a sunny spot.
This collection of articles will help you answer your questions:
https://www.gardeningknowhow.com/ornamental/flowers/dianthus
? Planted 2 months ago after purchasing from nursery.
Unfortunately, it seems that they did not transplant well! The heat struck a little earlier than usual for the East this year, so it made transplanting a little more difficult than usual. If they do not make a recovery, than an autumn planting may be more suitable.
https://www.gardeningknowhow.com/ornamental/flowers/dianthus