Despite their ethereal look, gardenias (Gardenia jasminoides) can take frost and even a brief freeze with little damage, but the evergreen is not immune to the cold. Hardy from U.S. Department of Agriculture plant hardiness zones 7 or 8 to 11, depending on cultivar, the shrub can live in temperatures down to 20 degrees Fahrenheit, with some cultivars able to withstand zero degrees. Gardenias that are damaged by cold can show yellow leaf burn, dropped buds and stem die-back, which most recover from in the spring. Pruning restores a freeze-damaged gardenia tree's good looks.
Monitor your cold-damaged gardenia, waiting for temperatures to remain consistently warm and for new growth to begin on any part of the plant. Don't pick up the pruners until there is no chance that cold will return.
Wipe away any dirt or debris from the blades of your bypass pruners with a paper towel or soft-bristle brush, if necessary. Spray the blades with household antiseptic cleaner and dry them with a paper towel. This eliminates any potential of transferring plant disease or fungus from other plants pruned with the tool.
Cut away dead or damaged plant material, cutting 1/4 inch above the first swelling bud below the damaged area of the stem with bypass pruners. Make the cut at a 45-degree angle. Because gardenias bloom on last year's wood, you don't want to cut off any more than is absolutely necessary to avoid eliminating more of those lovely white flowers than you have to.
Scrape your fingernail or the edge of your pruner's blade lightly into the bark of a damaged stem when you don't see any signs of new growth to determine if it is really dead before you cut. A live stem shows a layer of green just below the bark. Work from the tip of a damaged stem down, until you either see green or determine that the branch needs to be removed at its base.
Clean up any frost-burned leaves or buds that have dropped around the gardenias to eliminate hiding places for insects and fungal disease. Leave damaged leaves on live stems. Broadleaf evergreens, such as gardenias, push out new growth to replace damaged leaves as the growth begins.