From our perspective as plants, our very existence is dictated by our genetic blueprint, which is shaped by our native environment. We oleanders (Nerium oleander) originate from the warm, Mediterranean climates of Southern Europe and Asia. Our physiology is fine-tuned for heat, sun, and well-drained soil. This means our cellular structure is not designed to endure prolonged, deep freezing temperatures. Unlike deciduous trees that enter a deep dormancy, our version of dormancy is shallow. Our sap does not possess the same potent natural antifreeze (like specific proteins and sugars) that true cold-hardy species produce in abundance to prevent ice crystal formation within our cells.
When the air temperature plummets below freezing, the water within our cells begins to freeze. This is a catastrophic event for us. As water turns to ice, it expands, forming sharp, needle-like crystals that physically pierce and rupture the delicate cell membranes and walls. This is the primary cause of freeze damage. You will see this manifest as blackened, mushy leaves and stems shortly after a freeze event. This is essentially necrotic tissue—the parts of us that have died because our cells were destroyed from the inside out. The severity is directly tied to the depth and duration of the freeze. A brief, light frost may only damage the most tender new growth and leaves, while a hard freeze (below 25°F / -4°C) for several hours will cause extensive damage to stems and major branches.
Our primary strategy for surviving a freeze does not rely on our above-ground foliage or stems. Our hope for regeneration lies protected at our base, at the root crown—the junction where our roots meet the stem, located at or just below the soil surface. The soil itself acts as an insulating blanket, protecting this vital zone from the coldest air temperatures. Even if all our above-ground growth is killed back to the ground, the root crown and root system below may still be alive if the freeze was not severe enough to penetrate deeply into the ground. Within the surviving parts of our stem and root crown, we hold dormant buds. These buds are waiting for the signal of warmer temperatures and longer days to break dormancy and initiate new growth.
Our ability to withstand a freeze is not a fixed number but is influenced by our overall health and, crucially, the process of acclimation. As autumn progresses and temperatures gradually decrease, we undergo a hardening-off process. This slow cooling triggers physiological changes, allowing us to increase sugar concentration in our cells and reduce water content, thereby mildly boosting our frost tolerance. A healthy oleander, well-watered going into winter and not stressed by drought or disease, is far more likely to survive a freeze than a weak, stressed one. A sudden, dramatic temperature drop before we have had time to acclimate is far more damaging than a similar cold snap after weeks of cool weather.
Following a freeze, the true test of our survival is not immediately apparent. It is essential to wait until the spring, when consistent warmth returns, to assess the damage. The blackened, dead growth acts as a protective layer for the tissue beneath it. Once the danger of frost has passed, new shoots should emerge from the base or from lower stems that retained life. This regrowth is proof that our core—the root crown and root system—has survived. Our energy reserves, stored in our roots, will fuel this comeback. However, if the freeze was exceptionally severe or prolonged, penetrating deep into the soil, it can kill the root crown and roots, meaning we will not return.
