Cover your gardenias with a blanket or cardboard box during winter cold snaps. Since gardenias are extremely cold sensitive, they will require adequate insulation and protection from harsh winter winds.
Secure a cardboard box large enough to cover the shrub without bending the branches. Use old blankets, straw, or bubble wrap to insulate the plant while it is under the cardboard box.[15]
Despite your best efforts, the tips of the branches may die and turn black from frost or cold damage. When this happens, prune the branches a couple of inches below the damage with sharp pruning shears.
Alternatively, you could transplant your gardenia to a pot and bring it inside for the winter. Though your plant will face higher chances of bug infestation, there are steps you can take to better care for your gardenia indoors.