Most things I've read say NOT to trim/prune, that cutting too far back may actually kill the plant. If they look REALLY bad, maybe just take off the brown tips (if you've got the time), otherwise try letting some of the plants just cover over their own brown spots. Good Luck
P.S. I'm thinking of getting some of these myself, so I'm glad to hear they really DID bloom all summer!

they do benefit from a sweet soil ,a top dressing of horticultural lime, and some bonemeal, should pick them up.Be sure to scratch it in lightly and water well.If their soil is depleted,use a top dressing of a good sandy loam.Light and friable,sharp drainage is essential.Marvelous plants that require little fertilizer or fuss.I have sheared off spent bloom ,but never ,live leaf.They will send out fresh new growth and the old leaves will wither away and can then be plucked out.-D

How do you like the fragrance, Roseperson? Is it very fragrant? Is it clovelike?

I have a single really red dianthus that does not bloom all summer, but is wonderfully fragrant. Would like to have another really red that blooms continuously and is very fragrant also.

Thanks....Takate

I've seen this plant in catalogs and looks good, but I thought Dianthus was a biennial. Does it reseed or itself or does this variety not die off after a couple years?