Jalapeño pepper plants (Capsicum annuum) are native to tropical and subtropical climates, meaning they thrive in warm conditions. Their genetic origin makes them highly sensitive to cold temperatures, unlike hardier vegetable varieties. This sensitivity is a major consideration for gardeners, as cold exposure can quickly halt growth or even kill the plant. Understanding the specific temperature tolerances is the first step toward a successful harvest season.
Defining the Critical Cold Thresholds
The temperature at which a jalapeño plant experiences stress occurs well above the freezing point. When temperatures consistently drop below 60°F, the plant’s metabolic processes begin to slow significantly, often leading to a stall in growth. Sustained nighttime temperatures in the 50°F to 55°F range cause the plant to enter a protective mode, resulting in yellowing leaves and the dropping of flowers and small fruit.
The absolute lethal threshold for a jalapeño plant is at or below 32°F. Even a light, short-duration frost is typically enough to cause irreversible damage to the plant tissue. Mature plants may withstand a brief dip to 45°F for a few hours, but freezing temperatures are highly likely to result in death.
Understanding Chill Injury vs. Frost Damage
The two main ways cold harms a jalapeño plant are through chill injury and frost damage, each having a distinct physiological mechanism. Chill injury occurs at low but non-freezing temperatures, typically between 35°F and 50°F. This damage is metabolic, causing cellular dysfunction that reduces the plant’s ability to absorb water and nutrients. Symptoms appear over time and include stunted growth, wilting, and a gradual yellowing or bronzing of the leaves.
Frost damage, by contrast, is immediate and destructive, occurring when the temperature reaches 32°F or lower. The water inside the plant’s cells freezes, forming sharp ice crystals that physically rupture the cell walls. This results in tissue that looks blackened, water-soaked, and collapsed once it thaws. Recovery is unlikely because the plant’s internal structure has been destroyed.
Short-Term Cold Protection Methods
When an unexpected cold snap is forecast, temporary protective measures can shield plants from short-term damage. One effective method is covering the plants with row covers, old blankets, or cardboard boxes, which traps heat radiating from the soil. The covering should extend to the ground to ensure the warmed air is contained around the plant canopy.
Potted jalapeños should be moved indoors to a garage, porch, or against a south-facing, warm wall. Before a predicted deep freeze, thoroughly watering the soil is beneficial, as moist soil retains heat better than dry soil. For in-ground plants, temporary barriers like cloches or water walls can be used; the water in these containers absorbs solar energy during the day and releases heat slowly throughout the night.
Preparing Jalapeños for Overwintering
For gardeners aiming to keep a productive jalapeño plant for a second season, overwintering is necessary to induce dormancy. The plant must first be harvested of all remaining fruit and then heavily pruned, cutting back the main stems to create a small framework. This drastic pruning reduces the plant’s need for light and energy over the winter months.
The plant must then be repotted into a smaller container with fresh soil after cleaning the roots to remove pests. The overwintering location should be cool, ideally between 55°F and 65°F, and require minimal light to maintain a dormant state. Watering must be reduced significantly, usually to once every one or two weeks, as the plant is not actively growing and is highly susceptible to root rot.