Arabian Jasmine (Jasminum sambac) is a tropical evergreen plant native to a warm climate zone spanning from South Asia to Southeast Asia. Its physiological processes, including photosynthesis, respiration, and cellular function, are optimized for consistently warm temperatures. The ideal temperature range for vigorous growth and prolific flowering is between 60°F and 90°F (15°C and 32°C). At these temperatures, enzymatic activity is efficient, water uptake through the roots is balanced with transpiration from the leaves, and new growth develops without stress. When temperatures fall below this comfort zone, the plant's metabolism begins to slow down significantly. This slowdown is the first sign of cold stress, manifesting as a halt in growth and a cessation of flowering.
Cold stress, particularly frost and freezing temperatures, inflicts direct physical damage on the plant's cellular structure. Arabian Jasmine is not frost-tolerant. The primary mechanism of damage is the formation of ice crystals. When temperatures drop below freezing (32°F or 0°C), the water within the plant's cells can freeze. These ice crystals puncture the cell membranes and walls, which are crucial for maintaining cell integrity and function. Once these membranes are ruptured, the cell contents leak out, and the cell dies. This damage is visible as blackened, mushy leaves and stems. Even before freezing occurs, chilling injury can take place at temperatures above freezing but below 50°F (10°C). This injury disrupts metabolic pathways, impairs nutrient uptake, and can lead to leaf chlorosis (yellowing) and drop as the plant struggles to maintain basic functions.
From a horticultural perspective, the survivability of a plant in winter is defined by its USDA hardiness zone rating. Arabian Jasmine is typically classified for USDA zones 9 to 11. This means it can only survive winters outdoors in regions where the average annual minimum temperature does not fall below 20°F to 30°F (-6°C to -1°C). In the warmest parts of zone 9, a mature, well-established plant in a sheltered location may survive a brief, light frost with some leaf damage but will likely die back to the ground. However, any sustained period below 25°F (-4°C) will almost certainly be fatal to the above-ground parts of the plant and can kill the root system if the soil freezes. Therefore, for the vast majority of temperate climates that experience a true winter with consistent freezing temperatures, Arabian Jasmine cannot survive outdoors.
In regions that are on the borderline of the plant's hardiness (e.g., parts of zone 9), certain strategies can be employed to improve its chances of survival. These measures aim to mitigate microclimate conditions. Planting the jasmine in a south-facing location against a warm wall can provide radiant heat and protect it from harsh northern winds. Applying a thick layer of organic mulch (4-6 inches) around the base of the plant is critical. This mulch acts as an insulating blanket, protecting the root zone from freezing temperatures. If a light frost is forecast, covering the plant with a frost cloth or blanket can trap geothermal heat rising from the soil, preventing frost from settling on the leaves. For container-grown plants, which are more vulnerable because their roots are exposed to ambient air temperatures, the only reliable survival strategy is to bring the plant indoors before the first frost.
For gardeners in climates colder than zone 9, overwintering Arabian Jasmine indoors is the only way to ensure its survival. This process involves a significant environmental change for the plant. It should be brought inside when nighttime temperatures consistently drop into the 40s°F (4-9°C). Once indoors, the plant will often enter a semi-dormant or rest period due to lower light levels. It should be placed in the sunniest window possible, preferably a south-facing one. Watering should be reduced significantly, allowing the soil to dry out more between waterings, as the plant's water requirements are much lower when it is not actively growing. The plant may drop some leaves as it acclimates to the lower humidity and light levels indoors. This is a normal stress response. With proper care, it can be moved back outdoors after all danger of frost has passed in the spring.
