Can I split a dianthus plant?

Dianthus have just one stem and so can't be split. However, if it has been spreading everywhere then it is likely that some of the spreading stems have rooted themselves and these rooted sections can be carefully removed and replanted (known as Irishman's Cuttings). Otherwise you will have to trim the straggely edges and maybe take softwood cuttings in spring.

Thanks Bulbaholic - I've given it a good haircut and it's shrunk tremendously.

use some of the trimmings to make heel cuttings then you will have new plants too. you can get them to root in a glass of water on the window sill. when growing well pot on in compost and then harden off in a cold frame ready for planting out next spring.

Thanks Seaburngirl - I'll give it a go