Answer: Your zip code places you in zone 6B, the warmer part of zone 6. Depending on your microclimate you might add or lose a half a zone depending on how sheltered your planting site is, if there is wind protection (especially in winter) and so on. Based on your description I do not think this would be at all suited to a gardenia. One alternative might be to grow it in a container and bring it into a sheltered location during the winter, however gardenias are quite difficult when it comes to overwintering them indoors.
If you want to grow broadleafed evergreens there, you may want to consider some sort of windbreak to help them overwinter in better condition. If you want the fragrance and a broadleafed evergreen, you might consider the Sarcococca hookeriana var. humilis or Himalyan sarcococca. This is fairly low growing but the fragrance is just amazing.
Your local professional nursery staff should also have suggestions based on a more detailed understanding of the growing conditions where you are planting as well as your overall design goals.
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