Are these potted trees? Have you considered cutting your losses and buying new, fresh, non-potbound trees when you are able to plant them? Keeping them in the greenhouse isn't going to work. Anything else is going to depend on the details. Tell us a little more about what's going on.

p.s.

...and from the description of your garage (never gets close to freezing), that probably isn't going to work either.

They NEED to be cold over the winter. The greenhouse temps are basically summertime temps, so that won't won't work.

Why not just keep them outside? They're hardy in you zone. To protect the roots (since container roots are more exposed) you can do a few things, including something as simple as mulching around the pots with leaves, bark mulch, etc.

Or place them up against the house.

Thank you guys. The trees are in pots from the store still, and I will buy new ones in the spring if need be, but I just felt the urge to save these poor guys.
I think I may just keep them outside, but I was told at the store that they would not survive in the winter in their pots. I can put them against the side of my house, which is brick. Other than the leaves/mulch, are there other ways of the protecting the roots? I'm trying to weigh all options at this point.
Thank you again-

i am in adrian mi ...

HEAL THEM INTO MOTHER EARTH IMMEDIATELY ....

they are trees .. the ground is not frozen .. and wont be for a month ...

they are not house plants ..

you ware way overthinking this ..

slip them out of the pots.. and plant them one foot apart to do it fast ...

proper placement can be done as soon as the ground thaws in late march ...

i am doing the same with 6 conifers today or tomorrow ...

ken

i am in adrian mi ... [i have no idea how i got it in my head, that you were in mi???? so feel free to ignore the ground freeze stuff and what not .. lol ...]

HEAL THEM INTO MOTHER EARTH IMMEDIATELY .... [still correct]

they are trees .. the ground is not frozen .. and wont be for a month ... [probably wont]

they are not house plants .. [still correct]

you ware way overthinking this .. [still correct]

slip them out of the pots.. and plant them one foot apart to do it fast ... [still correct]

proper placement can be done as soon as the ground thaws in late march ... [still correct as to placement next spring .. but i dont know about that date]

i am doing the same with 6 conifers today or tomorrow ... [still am doing it here in MI]

ken

Now is the time to plant.