The jalapeno plant, a popular cultivar of Capsicum annuum, is a warm-season annual highly sensitive to temperature fluctuations. Successful cultivation relies on maintaining specific thermal conditions that support growth and fruit development. Understanding the upper and lower temperature limits is necessary for a productive harvest.
The Ideal Temperature Range for Growth
Jalapeno plants thrive within a specific temperature range that maximizes their metabolic processes and fruit yield. The optimal daytime temperature for vigorous growth is typically between 70°F and 85°F (21°C to 29°C). Within this window, the plant can perform efficient photosynthesis, which converts light energy into the sugars needed for growth and fruit production. Nighttime temperatures are also significant, ideally remaining above 60°F (16°C) for consistent performance. If night temperatures fall below this level, the plant’s metabolic activity slows down considerably, which can interfere with flower development and fruit setting.
The Critical Cold Threshold and Frost Damage
Jalapeno plants are highly susceptible to cold stress, which begins long before freezing occurs. Chilling injury can start when temperatures fall below 55°F (13°C). This non-freezing cold exposure causes cellular dysfunction, weakening the plant’s tissues and reducing the ability of the roots to absorb and transport water.
Visible signs of chilling injury include wilting, discolored or darkened leaves, and a general cessation of growth. Prolonged exposure to temperatures below 55°F can lead to symptoms resembling nutritional deficiencies, and plants often struggle to recover from this type of stress. The absolute cold limit for a jalapeno plant is 32°F (0°C), as any temperature at or below this point will cause immediate frost damage.
Frost damage is devastating because the water inside the plant’s cells freezes, forming sharp ice crystals that rupture the cell membranes. This results in rapid tissue death, visible as blackened, water-soaked, or desiccated stems and leaves. To protect plants from cold snaps, gardeners can use row covers or cloches to trap ground heat, which can provide a few degrees of necessary insulation.
For container-grown jalapenos, move them to a sheltered location, such as a garage or indoors, when temperatures are forecast to drop below 40°F. Applying a thick layer of organic mulch around the base of in-ground plants also helps insulate the soil and roots from sudden temperature drops.
Symptoms and Management of Excessive Heat
When temperatures exceed the optimal range, jalapeno plants experience heat stress, with the upper threshold considered to be above 90°F (32°C). The most common problem is “blossom drop,” where the plant sheds its flowers before they can be pollinated to set fruit. High temperatures can compromise the viability of the pollen and interfere with the fertilization process, causing the plant to abort fruit production.
Heat stress can also manifest as sunscald on the fruit, appearing as white, dry, or leathery patches on the side facing the sun. This damage occurs when intense sunlight overheats the fruit tissue, causing it to bleach and become necrotic. Leaves may wilt during the hottest part of the day as the plant attempts to slow water loss through transpiration.
To manage excessive heat, providing temporary afternoon shade is an effective technique. A shade cloth can be draped over the plants to reduce the ambient temperature and protect the fruit from direct sun exposure. Increasing the frequency of watering is necessary to ensure the plant has enough moisture to cool itself. For potted plants, relocating them to a spot that receives shade during the peak afternoon heat can prevent immediate stress and blossom drop.