If you have the Gardenias with variegated leaves, it would probably be a good idea to cover them. I lost several last winter and my lowest temperature was 10°F.

I have never protected and have not had problems with the green-leaf varieties, even when the temperatures fall to Zero and a few degrees below that mark. None are potted, all are planted in the garden. If you have potted one's, I would suggest protection if the temperatures fall into the teens or below.
All of mine were killed to the ground, during January 1985, when the temperature was -12°F. for two successive nights, but the roots survived and they eventually recovered.

I don't grow the Tea Olive, but have two types of variegated Osmanthus and only one of those, 'Goshiki', which are grown in pots, is protected when the temperature falls below 10°F. The Tea Olives can withstand winter temperatures of -5°/-10°F., when planted in the ground. The foliage can be damaged by late freezes in the spring, but recover rapidly with warm sunshine.

If you decide to cover your plants, be sure to uncover them during warmer and/or sunny days.

Opps. I haven't even thought about my gardenia and tea olive. I do seem to remember though, that the most damage comes when the temperture rapidly drops from a warm spell, catching them off guard, so to speak. I don't think that was the situation this time.

Great to know. Thanks!

Right. I almost lost my creeping gardenias in the Easter Freeze of 2007, but they don't suffer if it gets this cold in the winter. Of course I'll find out this spring if that is true. I am concerned about some of my tea roses. I normally don't use any winter protection so I may have more winter damage than normal this spring.