Slow growing trees, many gardeners assume camellias are merely shrubs. Over several decades, they reach small treelike size, anywhere from 10 to 25 feet tall and 5 to 15 feet wide, depending on the species. While many varieties exist, most are selections or hybrids derived from these species: Camellia japonica, Camellia sasanqua, Camellia oleifera and Camellia reticulata. All camellias are best grown where winters are cool to mild.
Different camellia species and cultivars demonstrate varying tolerance to the freezing temperatures in winter. Both Camellia japonica and Camellia sasanqua survive low temperatures down into -17.8 to -12.2 degrees Celsius (0 to 10 degrees Fahrenheit) range. Camellia reticulata does best where temperatures don't drop below -9.44 degrees C (15 degrees F) for very long. Camellia oleifera is among the most resilient to cold, tolerating -23 degrees C (-10 degrees F) without damage.
Using hardiness temperature guidelines, and planting in the appropriate climate, camellias don't sustain damage from winter freezes as long as it never gets below -6.667 degrees Celsius (20 degrees Fahrenheit). Once winter cold drops below that, especially for extended periods, camellia leaves and flower buds are negatively affected. Intense cold causes the most exposed leaves, on branch tips, to scald and turn shades or brown. Flower buds also brown. The cold causes the cell tissues to rupture and desiccate. Flowers may still open, but petal tips may be brown while the protected core is normally coloured.
Dealing with freeze damage
Resist the urge to immediately prune away any cold-damaged leaves and flower buds on your camellia shrub. Although unsightly, the dried leaves and twigs insulate the lower, interior tissues of the shrub and provide protection against further dieback the rest of the winter. Do not scrape or melt ice or snow off the plant, let weather conditions dictate that. Hold off pruning until the spring after any flowers open. New growth will occur below pruning cuts on branches in early summer and mature in time for the fall.
While you can't change the weather, you can take precautions to limit the extent of cold on camellia trees outdoors when excessive freezing temperatures threaten. Healthy plants, those not stressed by drought or disease heading into winter, are better able to survive the cold. Depending on camellia tree size, you can cloak it with frost wrap or cloth sheets to provide some temporary insulation on coldest nights. Then, once spring returns, keep the soil evenly moist and fertilise to encourage healthy new growth to replace the damaged tissues pruned away.