Gardenias thrive in mild conditions, although they usually survive light frost conditions with minimal or no damage, according to the University of Florida Extension. You should bring gardenias indoors or cover them if you expect a hard freeze, because this can seriously damage the plant.
Gardenias are zone 8 plants, meaning they should survive temperatures as low as 15 degrees Fahrenheit, according to the University of Arkansas Cooperative Extension Service. You should plant gardenias in protected areas that provide plenty of morning sunlight to warm them on cooler days. Choose an appropriate variety for your area, because the cold-hardiness of gardenias varies by type.
A mature gardenia plant survives mild winters with little or no suffering, but new growth can be more easily affected by even a light frost. For this reason, avoid fertilizing in the fall, focusing fertilization efforts in the warmer months instead. Proper springtime weather is also needed, with evening temperatures no lower than 40 degrees for buds to develop, according to Colorado State University Extension.
If your gardenias freeze, simply cut them back to ground level, as suggested by North Carolina Cooperative Extension. Many gardenias will sprout and grow again with the advent of warmer weather. Consider planting gardenias in containers that you can bring indoors in the event of a freeze.