peonies are perennials & they are supposed to be outside in the cold for zone 5. you should have buried them last fall in the ground. I don't know why you even brought them in at all. but, since you did what I would do with them is take them back outside, find a protected spot, like up near the house, put some leaves or a cover over them, & leave them there till spring. then this spring you should find a spot in the yard where you want them to be long term. peonies don't like to be moved around, so where~ever you put them is where they will stay. after you get them in the ground leave them there, even in the wintertime. that's where they want to be. they need the cold weather to be able to come back in the spring. just like tulips & daffodils. these should not be treated as annuals. they need the cold.

I brought them in hoping for them to stay dormant in the basement but it was too warm. I didn't know where I wanted to plant them last fall. If I take them out now the tops that have grown will freeze off. They are growing fine down there under lights. I am just wondering if they will be fine being that much ahead.

The best idea, in the event of being unable to plant in fall, would have been to bury the plants temporarily in the ground until spring, and mulched over top of them. Or, leave them in the garage. Peonies need a period of below freezing to grow and bloom..I'm not sure how long the dormancy period needs to last.

Personally, I would not recommend putting them outside at this point...but I think your best bet would be to contact a peony grower and ask for their advice. I think many are perfectly happy to give some email or phone advice.

At worst, you aren't out a bunch of cash, and you have learned your lesson!

I think the best thing you might be able to do for them now is to keep them under very strong light, but lower temperatures around 55F if you have a cooler room. They should stay fairly dormant with cooler temperatures and may have capability of producing some new growth in the spring.

I would suggest at least a 400 watt full spectrum metal halide or HPS light, and get the lights as close as possible without burning the leaves. 8-12 hours of light per day should be good enough. If you have a nice south facing window, then less light should be required.

Where did you find itohs for $10 ea.? I so want to try them but the cost is prohibitive.

I found them at my local nursery. They mark everything down really far in the fall so they don't have to keep it. They don't grow any perennials -just bring them in from somewhere else so they want to get rid of everything. I have gotten some real bargains there for sure.
The itohs are looking good down in the basement. I have them under good lights. I am not worried if they don't bloom this year. I will be happy to keep the vegetative growth alive until I can get them outside again.

What species do you happen to have?

I have around a dozen species of itoh peonies myself, but if you happen to have collected something really special, I may be interested in a piece of yours.

I purchased mine for more like $35 a piece, shipping included however I got nice big tubers that I managed to divide up immediately so I have multiples on my itoh peonies which are primed to wake up with many new buds in another month.

Here is a link that might be useful: Blog on some of my itoh peonies

I don't think any I got were special. Those wouldn't have been left at the end of the season. There is Copper Kettle, Julia Rose, Magical Mystery Tour and Lollipop.
From what I've seen $35 is a very good price especially if they were big tubers.

One of my plants Julia Rose has a beautiful bloom going in then basement now. I don't know what will happen once spring comes.
I can't believe how plants outside can survive drought with how much water these plants are taking!

I just wanted to make a comment because I did notice a huge difference in the performance of indoor tree peony seedlings vs the ones outdoors. The indoor ones appear to have less size potential, and they are green through the whole time, growing very thin and elongated.

The ones that are outdoors seem to start out red, and they will grow much larger, even though the indoor ones still experienced temperatures in the mid 50s which is enough to promote some vernalization.

They simply need to have outdoor conditions with all the precipitation, and temperature swings to do their best. I posted a blog with the comparison where the last couple of pictures show what indoor seedlings look like.

Here is a link that might be useful: peonies indoors vs outdoors

If you keep them under strong lighting, they should do fine.

They do look fine. They sure do take alot of water though! I can hardly wait until it is warm enough to move them outside-even if I have to bring them in every night!