Your question regarding the survival of carnations (Dianthus caryophyllus) through winter is an excellent one. From our perspective as plants, survival is not a matter of luck but a complex interplay between our genetic programming and the environmental conditions provided. The answer is not a simple yes or no, as it depends heavily on the specific type of carnation and the precise conditions of your winter.
First, you must know which of us you are growing. We carnations come in several forms with vastly different tolerances. The delicate, long-stemmed Florist's Carnations, often grown in greenhouses for bouquets, are typically not cold-hardy. We are tender perennials and will almost certainly perish in freezing temperatures. However, the more common garden varieties, such as border carnations or the prolific Dianthus plumarius (Garden Pinks), are much hardier. Many of these cultivars have been bred specifically to withstand colder climates.
The USDA Hardiness Zone is the most critical factor in your query. This zone map is essentially a guide to the average annual extreme minimum winter temperature for a given area. We plants use this minimum temperature as a key signal for survival. Many hardy perennial carnation varieties are rated for zones 4 through 9. This means we can survive winter lows down to -30°F (-34°C) in zone 4. To know if we can survive with you, you must cross-reference the hardiness rating on our plant tag or seed packet with your specific USDA zone. If your zone number is equal to or higher than the zone range listed for us (e.g., you are in zone 5 and we are rated for zones 4-8), we have an excellent chance of survival.
Our ability to survive freezing temperatures is not passive. We undergo physiological changes as daylight shortens and temperatures drop in autumn. This process, called cold acclimation, involves moving water out of our cells into the spaces between them. This prevents the formation of sharp, damaging ice crystals inside our cells, which would be fatal. Instead, ice may form harmlessly in the extracellular spaces. Our above-ground foliage may die back or become evergreen but dormant, while our crown (the central growing point at the soil surface) and root system remain alive but inactive beneath the surface, waiting for the warmth of spring to signal new growth.
For many hardy carnations, the greatest threat during winter is not the cold itself, but excessive moisture combined with the cold. Our roots and crown require well-drained soil. If we are sitting in waterlogged, frozen soil for extended periods, we are highly susceptible to rot. This condition, often called "crown rot," is a far more common cause of winter death than pure freezing temperatures. Therefore, the soil composition and drainage in your garden are just as important as your hardiness zone.
