Answer: Perennial dianthus will usually rebloom if deadheaded, and you can do that either trimming each bloom stem individually or by giving it an all over light shearing.
Browning of the foliage can have numerous possible causes. Many types of dianthus simply resent heat combined with humidity. They also require a well drained soil, meaning one that is not soggy. They tend to do poorly on a heavy clay-based soil unless planted on a slope or in a raised bed where the drainage is improved.
They do best in full sun with good air circulation, good drainage and a relatively lean soil, so be careful not to overfertilize and avoid overhead watering.
Also inspect the plant closely for signs of pests, they may also be attacked by spider mites which would cause a speckling and leave behind little webs. These can be treated with insecticidal soap according to the label instructions.
I hope this helps you trouble shoot.
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