I purchased a Hibiscus tree this past spring. I put it in a large vase and was advised to use pre-fertilized soil. It has done wonderful but not sure what to do with it this winter. I live in South Carolina.
Your Hibiscus can winter over outdoors in your zone 8 garden.
If the temperatures should fall below freezing, you should move the plant to a sheltered location, perhaps a garage.
Here is a link with more information.