From our perspective as snapdragons (Antirrhinum majus), the question of frost survival is not a simple yes or no. It is a complex interplay between our genetic programming, our life stage, and the severity of the cold event. We are classified as tender perennials, which means our inherent cold tolerance is limited and we are often grown as annuals in regions with freezing winters.
We are not equipped with the same deep, hardy survival mechanisms as true alpine or boreal species. Our cells contain a high water content, and when the temperature plummets below freezing (32°F or 0°C), this water begins to form ice crystals. These crystals are our greatest enemy; they puncture and shred our cell membranes from the inside out, causing the fatal damage known as frost kill. A light frost, where temperatures dip just slightly below freezing for a short period, might only damage our most tender new growth and flowers, which we can often recover from. A hard freeze, with temperatures below 28°F (-2°C) for an extended time, is almost always fatal to our above-ground foliage.
Our ability to withstand cold is profoundly affected by our stage of life. As mature plants, we have a slightly better chance. Our stems are woodier, and our root systems are established, providing a small reservoir of energy. However, we are most vulnerable as young seedlings or freshly planted transplants. At this stage, our tissues are exceptionally succulent and tender, offering little to no resistance to ice crystal formation. A frost that would merely wilt the leaves of an established plant will almost certainly kill a seedling outright.
We are not entirely passive victims to the cold. As temperatures begin to drop in the autumn, we undergo a process called cold acclimation. This is a slow, physiological hardening-off process where we start to move water out of our cells and into the spaces between them. While the water between cells can still freeze, it does far less damage there than ice forming inside the cell itself. Additionally, we may increase the concentration of sugars and other solutes in our cell sap, which acts like a natural antifreeze, lowering the point at which freezing occurs. This process requires a gradual temperature decline; a sudden, severe frost in early fall catches us unprepared and is far more damaging than the same frost later in the season after we have acclimated.
In milder climates (typically USDA zones 7-9), where winters are cool but ground-freezing events are brief, our survival strategy shifts. While our above-ground growth will almost certainly be killed back by a hard frost, our root crown—the crucial point where our stems meet the roots—may survive if it is insulated by a deep layer of mulch, snow cover, or fallen leaves. If this crown is protected, we can tap into our perennial nature and regenerate entirely new growth from this base when warmer temperatures return in the spring. This is not a guarantee, but it is our primary method for surviving a cold season.
