a rapid change in heat & light often results in a loss of leaves. IF the stem is still green andyou find live buds on the stem it will leaf out location i8n house have most light possible. reduce water (keep soil damp not wet) & it should leaf out. Trying to root hardwood cutting without leaf is very hard.

I'm afraid that gardenia's are very difficult to grow inside the typical home. You almost need greenhouse conditions (very humid, very bright, cool).

Thank you both for your responses. I do have two questions, however, for Georgez5il: (1) you said "...if the stem is still green...," do you mean if the stem is still green inside (i.e., pliable, like green wood) or outside? and (2) what do you mean by live buds? I will keep it in bright light, and try to keep it humid. Would it be beneficial to put a plastic bag over it to maintain humidity?

Thank you both soooo much.

As to stem Yes.....The buds should also be "green" not dried & brown/black.. tent (high humidity) will not help only promote fungal growth.....

I had the same issue with my gardenia once I moved it inside. My gardenina tree struggled in a morning sun, open-room area by patio doors. It lost a lot of leaves and had mostly bare stems. I lightly scratched some stems to reveal green wood underneath ( I knew it was alive), so I then move the 4 foot tree to my laundry room (8 x 10 feet). Although the room is unheated, it is warm and humid from many shoplights in starting seeds. I put a flourescent compact spiral light in a metal plug-in housing unit and kept it overtop of the gardenia. Between the warmth in the room, light intensity from the flourescent spotlight, and increased humidity, the gardenia has leafed out and even has flower buds now. It is prone to mealy bugs, but I keep an eye out on that and use alcohol swabs/mist to eradicate anything. If you could move the gardenia and create a warm microclimate inside of your house, that would work with a small light setup and increased humidity. You can even make a small greenhouse type plastic enclosure in your house, just big enough to enclose the gardenia with a light source, to trap humidity and heat. The spiral flourescent bulbs in 60 watts (high lumens) runs about $7.00 a bulb, with the metal unit about $5.00-both at Home Depot. Those cheap portable greenhouses would also work with the light setup. Good luck :)
ps gardenias inside are a lot of work, IMHO

I have a gardenia that I bring in the house each winter. It always struggles a bit but does not drop all its leaves. But one thing about them is that they like acidic soil. When the leaves of mine look yellow or start to turn brown I shove a handful of pine needles on top of the soil, or make a tea of pine needles and pour over the plant. My gardenia seems to love this.