Answer: Although the planting areas appear to be exactly the same, there are always slight differences in exposure to wind or sun, and there can also be differences in soil drainage. Do some checking on the one with brown leaves; scrape the bark from a stem or two to see if the tissue beneath the bark is green. If it is green, the soil drainage is probably okay and the leaves were probably exposed to stress from cold. New leaves should develop when the weather warms up. If the tissue beneath the bark is brown, it indicates the plant is either suffering from poor drainage or the top of the plant was nipped by frost or cold winter wind. It may or may not recover -you won't know for sure until new growth begins in the spring.
Best wishes with your gardenia's.
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