They are only hardy to about 45 degrees F. Prune them back anytime their length becomes excessive. Also, cut off any damaged stems and ones that have become leggy with little foliage. If healthy, the trimmings can be placed in water and left to root to create more plants.
Where do you prune sweet potato vines?
Cut back vine tips that have exceeded their boundaries. Make cuts roughly 1/4 inch above leaf nodes to encourage new growth. Prune off broken or sickly vines. The more of the vine that is pruned off, the more aggressively the plant will try to regrow.
More useful articles on a similar topic 👇
Should you remove potato flowers and/or their fruits?Do green sweet potatoes go bad?