I have 2 Aruba Wind Hibiscus’. I’ve had one about 3 years and the other about 1 year. I winter them in the house and haven’t had any problems until this year. Both of the plants were infested with aphids and white flies. I doused them both with insecticidal soap about once a week for three weeks. I think I have managed to get rid of the infestation but now the leaves are yellowed and fell or are falling off and I lost all the buds. Can I cut the bigger plant back so it won’t look so sickly?
Hibiscus trees do not over-winter very well indoors. They have to be pest-free when brought inside and they have to be right in front of a sunny window.
In the photos you provided, I can see that they are in pots that are too large and the potting soil looks to be too heavy without enough perlite mixed in. As a result, all of that extra heavy soil,is not drying out properly around the roots and the roots are starting to rot. That is what is causing so many leaves to fall off. The resulting stress makes the plants more vulnerable to pests.
Frankly, I think your plants are too far gone to try to save them. If you want to try, prune back all the stems to a length of 4-6 inches. Then genially remove the plants from their pots. Carefully let the excess soil fall away from the original rootball. Do not remove all of the soil or rinse the roots. If you see no healthy, firm roots then discard the plants. If there are healthy roots, leave the soil surrounding the healthy rots and discard the excess soil. Then, put the remaining roots into a smaller pot just barely large enough to hold the healthy roots and just enough soil to cover them. Perhaps with good light and proper watering you will be able to keep them alive until the warm weather returns.