How long has it been in the bag? If it has been more than two weeks I THINK I would cut some slits in the bag now, keep the soil moist and in a week or two open the top of the bag, then after a week or two lower the bag. I'm guessing this is in your house right? Keep it warm and give it whatever light and moisture that is required for it. Good luck. It sure looks great.

Thank you, oldlady!. It's been in bag for about a month now. I'll start removing bag for a few hours each day. But for this gardenia cutting I take bag off throughout the day and put bag back on at night. There's actually a flower bud now! :-)

I took some cuttings this fall from several gardenias in the yard. I had about 20 cuttings and just put them in a baby food jar full of water. Nearly all of them rooted. I threw 3 away that had clearly lost their luster, and the ones that'd rooted best I potted up. The remaining ones either didn't have roots (but were still glossy green) or had very few roots. I left them in the baby food jar full of water.

I'm at the point of potting up the remaining cuttings that've filled the baby food jar full of roots.

All that to say that as long as the gardenias don't get TOO cold, I bet you're not going to have a problem acclimating them, whatever you do. The ones in the baby food jar have just been sitting in a window (to my wife's chagrin). The idea of slitting the bags is a good one. An alternative is to remove the bags for gradually more and more time. I'd suspect, at least with the gardenias, you could probably get by with removing them completely.