Could you plant them in pots or do they have to be in the ground?
Yes, you can grow dianthus in pots. Just provide them with their usual growing conditions and they will be happy:
https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
can you split them
Yes!
Early spring before flowering or early autumn would be best.
https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
I planted it about three weeks ago and when I planted it it was blooming an a week after planmting it stoped blooming. I feed it and water it at the base and its full of bulds but thats all it does. its in a well drained area. I planted out of the pot. Should it have been divided into more plants. I dont know what to do can you help me.
There is always stress to the plant when transplanted, especially while in bloom. Most plants go into "transplant shock". It is actually better, in the long run, for the plant to concentrate on establishing a strong root system instead of on blooming. I would trim old blooms back and water as needed. When new leaf growth is seen, it may send up sporadic blooms during summer. Some varieties bloom for longer periods. Here is an article on dianthus care and varieties. https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
I have been given a Dianthus plant with bright red flowers. How can I tell if this a perennial or annual?
This article will help you.
https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
How should I prepare for winter -dianthus in northeast?
Nothing needs to be done in the fall. These plants will benefit from removal of dead stalks or stems and nothing more.
https://www.gardeningknowhow.com/ornamental/flowers/dianthus/growing-dianthus-plants.htm
I have a mound of Dianthus that needs dividing. Any special tips?
The best time of year to divide perennial dianthus is in the spring, just as new growth begins and when the plants are fully hydrated.
Dig around your clump of dianthus, going about 6 inches deep with a spade. Cut under the clump and push down on the spade's handle to lift the roots from the soil. For large clumps, you can cut right through the middle as necessary to lift up more manageable sections.
Use a garden fork and your hands to separate the clumps. In general, divide dianthus clumps into four or five sections, each with top growth and roots. Discard sections that do not appear healthy, which are often found in the center of the clump.
I was given a plant and think it's a variety of Dianthus, but not sure. Would appreciate help in identifying it.