Montbretia, 'George Davidson'
I purchased this plant in a small pot to put in a tall, large decorative vase for outside. Does it need to be planted in the ground or can I just get a larger pot as it grows? It looks gorgeous coming out of this vase.
When the pot becomes crowded, you can dig up the corms and divide them among more containers, larger containers, or plant some or all of them in the ground. 
You might want to bring the container indoors, to a basement or unheated garage, during cold weather to protect against freezing. Otherwise, you could dig up the corms in the fall and replant them in the spring. Another option would be to sink the entire pot into the ground in the fall, and place a heavy layer of mulch over it. Plants in containers freeze more easily than those in the ground, because they don't have sufficient soil around them to insulate them.
Treat them like any other bulb/corms, and allow the foliage to remain in place until it dies back. That enables the corm to store food, so the plant can grow and bloom again the following year.
You might want to bring the container indoors, to a basement or unheated garage, during cold weather to protect against freezing. Otherwise, you could dig up the corms in the fall and replant them in the spring. Another option would be to sink the entire pot into the ground in the fall, and place a heavy layer of mulch over it. Plants in containers freeze more easily than those in the ground, because they don't have sufficient soil around them to insulate them.
Treat them like any other bulb/corms, and allow the foliage to remain in place until it dies back. That enables the corm to store food, so the plant can grow and bloom again the following year.