Perhaps wait several more weeks to see if things improve. Gardenias are evergreen, though, and should have kept their leaves over the winter season, so it is likely that the cause is not just the stress of being planted and getting established, although that likely plays a part. Look for signs of disease or insects, and be sure that the plants are in their ideal spot, as far as lighting, non-soggy but moist soil, etc.
Another possibility is if your area had experienced a cold snap, such as around December 24 in 2022. If the plants did not have enough cold protection, it may have caused dieback to branches, flower buds, and possibly roots due to cold damage. Even though Atlanta experienced nighttime temperatures in the 10s and 20s around December 24, and Foolproof gardenia is hardy to Zone 7a (0 to 5F), some plants (especially when they are just being established in their new home) might have been vulnerable. In certain cases, plants can recover from cold damage, although several branches, and likely all flower buds for the next year’s blooming season, may be lost. Again, we’d suggest giving them a little more time, such as midsummer or so, to see if any leaves come out for the plants to make food over the growing season. If a plant’s roots have not been damaged, in certain cases, the plants can come back. The fact that one of the plants is starting to leaf out suggests that at least that one has a chance for recovery.
Perhaps wait several more weeks to see if things improve. Gardenias are evergreen, though, and should have kept their leaves over the winter season, so it is likely that the cause is not just the stress of being planted and getting established, although that likely plays a part. Look for signs of disease or insects, and be sure that the plants are in their ideal spot, as far as lighting, non-soggy but moist soil, etc.
Another possibility is if your area had experienced a cold snap, such as around December 24 in 2022. If the plants did not have enough cold protection, it may have caused dieback to branches, flower buds, and possibly roots due to cold damage. Even though Atlanta experienced nighttime temperatures in the 10s and 20s around December 24, and Foolproof gardenia is hardy to Zone 7a (0 to 5F), some plants (especially when they are just being established in their new home) might have been vulnerable. In certain cases, plants can recover from cold damage, although several branches, and likely all flower buds for the next year’s blooming season, may be lost. Again, we’d suggest giving them a little more time, such as midsummer or so, to see if any leaves come out for the plants to make food over the growing season. If a plant’s roots have not been damaged, in certain cases, the plants can come back. The fact that one of the plants is starting to leaf out suggests that at least that one has a chance for recovery.
Hope this helps!