dividing spreading dianthus without enough roots?

I have several varieties of "pinks" that spread sideways in all directions and flop (especially the bluish-stemmed ones), but don't create extra roots as they spread. I've tried rooting clumps of cuttings ( cutting them back on top and adding rooting hormone) but they start rotting before they root. Does anyone have any ideas or success dividing these?

Flopping over is not really the same as spreading, my guess is they're not at a stage where they're ready to be divided yet. If you don't like the floppiness then you'll have to either stake them, or if it's cultural conditions (lots of water and/or fertilizer, and/or not quite enough light) that are causing them to be floppier than they should be then you can try and correct those conditions and see if it helps.

My experience has been that eventually those flopped over portions do put out tiny roots. I have separated them and rooted them in pots w/hormone, but it is slow. It is frustrating - something that seemingly spreads so well, yet is difficult to propagate.

Thanks, cedar. I guess I'll keep trying. Definitely frustrating when you have a plant that's spreading all over the place but seems to have no more roots than it started with!