Certified GKH Gardening Expert
If your hibiscus are kept indoors year-round or are outdoors now, you can fertilize based on these guidelines for tropical hibiscus:
If your hibiscus plants are indoors for the winter and they are usually outdoor plants, it's best not to fertilize now. The issue in this case is usually the lower light levels, so giving them more light, such as with a grow light, should help them fill out. Wait until spring, then fertilize.