Posted: 25/10/2016 at 16:44
Looks like a dahlia to me - herbaceous perennial which is not reliably hardy except in mild areas. Once the first frosts have blackened it, you need to dig up the whole root which will be tuberous so be careful and use a fork to lift the whole clump. Cut off the stems at about 2" high and then turn the plant upside down and let it drain for a day or so on some old newspaper in a frost free place.
Then you need to turn it right way up again and store somewhere frost free, wrapped in newspaper or in damp sand until spring. Then you spread the tubers in a shallow tray of potting compost, give it a drink and, again, keep it frost free but somewhere light. As the new shoots get to about 3" high you can take some off to make cuttings. Once the frosts are over in mid May or so you can plant it out in teh ground or in a big pot of your prefer. Protect the young growth from slugs and sanils who think of it as caviar.
Alternatively, if you are in a mild area, remove the frost blackened stems and cover it with a thick pile of good garden or bought compost to protect the crown from frosts and wait for it to make new shoots late next spring.