Answer: There are different types of dianthus. Most will rebloom at least once if the old flowers and stems are trimmed off. Some are more tolerant than others of hot, humid summers--the yellowing you see may be the result of fungal problems during wet or humid weather. Full sun, good air circulation will help limit that problem. Dianthus as a rule require good drainage, so overwatering or excess rain combined with a heavy soil or poorly drained location could also cause yellowing. Finally, the biennial Sweet William grows foliage for a year, survives a winter and blooms the second year, then turns brown and dies off. It is usually replaced by seedlings and forms an apparently perennial patch. This could be the plant you have, too.
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