What you dont say is how mature the plants are now. If you planted them in decent sized containers and have been taking care of them then I would expect them to have started to flower by now or at least have buds.

If you are zone 4 like me, then you only have another month and a half of growing season (if we are lucky). I still have a couple of plants that haven't flowered, but they are over 4 ft tall, and I have been bringing in big bouquets every other day or so since mid-July from most of my plants.

I would go ahead and put them in the ground. Even if you dont get many flowers this year, the leaves will feed the tubers and they should be fine for next year.

Due to being out of the country one year, I only had mine in the ground from mid-July to mid-September. Most of them came back fine the following year.