Don't bother putting pesticide in the soil prior to planting. It won't do any good. It is much better to treat a problem if and when it shows up. That way you can also choose the best product to match the problem.
I think you are too far north for those plants. Ixora is very tropical and is only hardy to zone 10. Hibiscus could be the tropical type (Hibiscus rosa-sinensis) which would not be hardy. Or it could be the perennial type (Hibiscus moscheutos) which is fully root hardy in your area although the tops will die back in the winter.
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