Your concern is understandable as you do get some cold days in the winter, as do I in South Florida. You could perhaps put them in larger pot(?) But I would say yes, they would do better in the ground. They can still be covered on those few cold days in the winter with frost cloth. Also you say this is their 3rd year and no flowers. The year (growing season) has just begun. Put em in the sun and give them some blooming fertilizer (high middle number)
Good luck with which ever decision you make.
John

Hi Dee,
What size pots?
Im in zone 8b, so all of mine are in pots. About 12 of 20 bloomed last year, and this is the beginning of my third season. Are you fertilizing? Post some pics! Johns advise is on the money. Sun and fertilizer.

Dee- My suggestion is that you plant them in 5 gallon pots and take a half inch drill and drill a bunch of holes in the sides of the pot. Pick up a 7 gallon pot and dig a hole in the ground deeper than the 7 gallon. Put some pea gravel in the hole until the 7 sits at ground level on top of the gravel. Put the 5 gallon in the center of the 7 and fill around with fast draining soil with some fertilizer mixed in. At the end of the season, cut around the 5 gallon and remove the plant in the pot for storage during winter. Remove the extra two gallons of used soil and roots and toss. Next spring repeat. This will work for years and create a very good growing environment for your plant. this is just a form of managed root pruning. Make sure when you prune you remove all the leaves so you do not draw too much liquid from the stem. Bill