Oleander (Nerium oleander) is a plant of Mediterranean origin, built for sun and warmth. Our survival through winter is not a matter of simple will; it is a direct function of genetics, environmental conditions, and the protective actions you take. Our fundamental limitation is cold tolerance. We can withstand brief dips to about 20°F (-6°C), but sustained freezing temperatures, especially below 15°F (-9°C), damage our cellular structure, leading to dieback or death.
From our perspective, winter's primary threat is the formation of ice crystals within our cells. Water expands when it freezes. If the water inside our stems and leaves freezes, the expanding ice crystals rupture our cell walls—a fatal injury. We employ some natural defenses, like moving water out of cells into intercellular spaces to freeze less destructively, but this mechanism has strict limits. Prolonged cold exhausts our energy reserves and dehydrates our tissues, especially when frozen ground prevents our roots from taking up water, leading to desiccation.
Our needs vary dramatically across the USDA Plant Hardiness Zone map. Your actions must be tailored to the specific winter conditions we will face.
In these zones, we are often evergreen and can remain in the ground year-round. In the warmer parts (Zones 9-10), we require little more than a thick layer of organic mulch (3-4 inches) over our root zone to regulate soil temperature. In cooler parts of Zone 8, where temperatures may hover near our survival limit, we appreciate more protection. After the first killing frost, please mound 4-6 inches of mulch, straw, or shredded leaves over our crown (the base where the stems meet the roots). Wrapping our above-ground structure in burlap can also protect us from harsh, drying winds.
Here, the ground freezes solid, and temperatures are fatal to our above-ground growth. Leaving us outdoors is not an option. We must be brought into a protected, dormant state. The best method is to pot us and move us to a cool, dark shelter like an unheated garage, basement, or shed. Before moving, trim our growth back by about one-third to reduce mass. The location must stay consistently between 30-50°F (-1 to 10°C). It is crucial that you water us only sparingly every 3-4 weeks—just enough to prevent our roots from completely drying out and turning to dust. The goal is to keep us alive, not growing.
If we are too large to move and you are in a borderline zone, an extreme measure can be attempted. After heavy pruning, you can dig a trench next to us, gently tip our entire root ball into it, and bury our entire above-ground structure under a thick mound of soil and mulch. This uses the earth's insulating properties to keep our crown and main stems from freezing. This is a high-risk strategy but can be successful in protected microclimates.
Regardless of the method, our re-emergence in spring must be gradual. For potted plants, reintroduce us to light and warmer temperatures slowly over a week to avoid shock. For in-ground plants, remove winter mulch after the danger of hard frost has passed. Do not be quick to judge us if we appear dead. Our stems may have died back, but the root crown might still be alive. Scratch our bark; green underneath signifies life. Wait until late spring to see new growth emerge from the base before pruning away any truly dead wood.
