From our perspective, winter is not a time of death but of deep, essential rest. As gardenias (Gardenia jasminoides), we are evergreen shrubs, meaning we do not drop all our leaves and enter a state of complete dormancy like deciduous plants. Instead, our metabolic processes slow dramatically. Our root activity diminishes, and our growth ceases. This period of quiescence is crucial for our survival, but our tropical and subtropical genetics make us extremely vulnerable to freezing temperatures. Our sap contains water, and when it freezes, it expands, rupturing our cell walls from the inside out. This causes the blackened, mushy foliage and stems you see after a hard freeze—it is fatal damage to our vascular system.
Our roots are our lifeline, and protecting them is your single most important task. While our leaves may endure a light frost, frozen soil is a catastrophe. Cold soil paralyzes our root hairs, preventing them from absorbing water. Meanwhile, winter winds wick moisture from our leaves, creating a condition known as "winter desiccation" or freeze-drying. We essentially die of thirst. A thick, insulating layer of mulch (4-6 inches) of pine straw, shredded bark, or oak leaves around our base is like giving us a warm blanket. It buffers the soil from rapid temperature swings, prevents it from freezing solid, and retains precious moisture. Ensure the mulch is not piled against our main stem, as this can encourage rot.
Our broad, dark green leaves are designed to capture sunlight, but in winter, they become large surfaces that radiate heat away, making us more susceptible to cold. Sudden, harsh morning sun after a freezing night can also cause severe damage by rapidly thawing our frozen tissues. Physical barriers are highly effective. Wrapping our canopy with burlap or commercial frost cloth on a frame staked around us creates a microclimate that traps ground heat and protects us from biting winds and sunscald. It is far superior to plastic, which can "cook" us on sunny days and offers no breathability. For potted specimens like us, moving us to a protected location—a garage, shed, or porch—that stays cool but above freezing is the ideal strategy to avoid the cold entirely.
Our watering needs change in winter, but they do not disappear. We require consistently moist, but never soggy, soil. As mentioned, desiccation is a grave threat. Water us deeply before a predicted hard freeze; moist soil retains heat far better than dry soil, providing an additional few degrees of protection to our roots. However, cease fertilization by late summer. Fertilizing too late in the season encourages a flush of tender new growth that is particularly sweet and vulnerable to cold damage. We need to harden off our existing growth and enter our dormant period without the push of excess nitrogen.
