My dianthus is turning brown from the middle. what am I doing wrong?

Question

There doesn’t seem to be any root rot, all of the roots are a healthy white?

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Answer 1

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