Jalapeños do best with days around 70 to 85°F and nights around 55 to 65°F. They are warm-season plants from the tropical highlands of Central and South America, and they are fussier about temperature than their tough reputation suggests.1Smart Gardener. Peppers: Jalapeño Early Frost kills them, and long chills below about 50°F slow and stunt them. The plant has two sets of limits: the temperatures that kill or injure it, and a narrower band that lets it set fruit. A jalapeño can look healthy through a hot or chilly stretch and still give you few peppers.
The Temperatures Jalapeños Like Best
Peppers grow best with daytime temperatures of about 70 to 80°F,2Smart Gardener. Peppers: Jalapeño Early and some growers stretch the good daytime range up to about 85°F.3Pepper Joe’s. Why Are My Pepper Flowers Falling Off: Causes & Solutions They prefer cool nights of about 55 to 65°F and fairly high humidity.4Smart Gardener. Peppers: Jalapeño Early That pattern matches the highland climate where peppers first grew, with warm days and cooler nights. A steady stretch of 80°F days and 60°F nights is close to ideal for flowering and fruiting.
Night temperature matters as much as the afternoon high. Nights warmer or cooler than the comfort zone both work against fruit set, even when the afternoons look perfect.
The range also guides planting dates. Wait to transplant until nights stay reliably above about 55°F, not just until the last frost has passed. Young plants set into cold soil and cold nights can stall for weeks. In hot-summer areas, the best fruiting often comes in late spring and early fall.
Your forecast comes from a weather station that may be miles away, and a low corner of the yard or a sheltered raised bed can run several degrees different, especially at night. A cheap min/max thermometer placed at plant height, out of direct sun, records the overnight low and the afternoon high so you can check both each morning.
How Cold Is Too Cold for a Jalapeño Plant
Jalapeños have no real frost tolerance, and a frost at 32°F can blacken leaves and kill tender plants. Freezing turns the water in plant tissue to ice crystals that break its cells.5Journal of Food Engineering. Comparison of freezing and convective dehydrofreezing of vegetables for reducing cell damage Once they thaw, frost-hit leaves and fruit turn dark, limp and mushy.
Cold above freezing also harms peppers.6Postharvest Biology and Technology. Melatonin ameliorates chilling injury in green bell peppers during storage by regulating membrane lipid metabolism and antioxidant capacity In the cold, pepper cell membranes stiffen from a fluid to a more solid state and begin to leak.7Postharvest Biology and Technology. Melatonin ameliorates chilling injury in green bell peppers during storage by regulating membrane lipid metabolism and antioxidant capacity At about 39°F, pepper cells show clear structural damage.8PubMed. Changes in Membrane Lipid Composition and Function Accompanying Chilling Injury in Bell Peppers Plants exposed to about 41°F grow poorly, with weaker growth than plants kept warm.9European Journal of Soil Biology. Gibberellin-producing Serratia nematodiphila PEJ1011 ameliorates low temperature stress in Capsicum annuum L.
Cool nights also hurt fruit. Nights of about 57°F or lower reduce the number of healthy pollen grains in each flower, so fruit that sets during cold nights is often misshapen and nearly seedless.10The Journal of Horticultural Science and Biotechnology. Influence of low night temperatures on sweet pepper flower quality and the effect of repeated pollinations, with viable pollen, on fruit setting In many pepper types, cold nights mean fewer flowers, fewer fruits and smaller peppers.11Preprints. The Effect of Night Low Temperature on Agronomical Traits of Thirty-Nine Pepper Accessions (Capsicum annuum L.)
After a chilly night, the leaves offer a clue to which kind of cold you had. Purplish or dull leaves and paused growth point to chill. Water-soaked, blackened leaves the next morning usually mean frost damage. Wait a few days before pruning, because damage often shows its true extent later, and a plant with live green stems near the base can regrow if warmth returns.
Jalapeños are perennial in frost-free climates, so you can bring a plant inside before frost and keep it going. Give it a bright spot away from cold drafts and windows at night. Expect leaf drop and little growth through winter, and move it back out only after nights warm into the 50s.
How Hot Is Too Hot for a Jalapeño Plant
Pepper seedlings have been kept alive for days at about 108°F.12PubMed Central. Heat-tolerant hot pepper exhibits constant photosynthesis via increased transpiration rate, high proline content and fast recovery in heat stress condition Survival is not the same as thriving, though. In a heat-sensitive variety, the plant’s food-making slowed sharply after a week at that heat, while a heat-tolerant variety kept going.13PubMed Central. Heat-tolerant hot pepper exhibits constant photosynthesis via increased transpiration rate, high proline content and fast recovery in heat stress condition The tolerant plant sweated more water through its leaves, which kept it cooler.14PubMed Central. Heat-tolerant hot pepper exhibits constant photosynthesis via increased transpiration rate, high proline content and fast recovery in heat stress condition Varieties held at about 104°F days and 95°F nights for two weeks differed widely in how they coped.15Scientia Horticulturae. Evaluation of heat stress response in pepper (Capsicum annuum L.) seedlings under controlled environmental conditions using a high-throughput 3D multispectral phenotyping
Dry soil makes heat worse. A thirsty pepper plant in high heat runs leaves about 7 to 9°F warmer than a well-watered one,16Preprints. Validation of Aeroponic Cultivation of Jalapeño Pepper (Capsicum annuum L.) through Thermal and Morphometric Characterization of Roots and Leaves so watering well before and during a heat wave helps the plant cool itself. Crowding matters too: in very hot, salty, dry conditions, planting jalapeños among tall corn cut their harvest badly.17Agronomy. Assessment of Intercropping and Plastic Mulch as Tools to Manage Heat Stress, Productivity and Quality of Jalapeño Pepper In hot spots, give plants room rather than packing other crops tightly around them.
Leaves drooping in the afternoon sun and perking up by evening are a normal response to heat, not a problem by themselves. If the plant is still wilted the next morning, the roots are short of water, so check the soil a few inches down and water deeply. Leaves that curl, turn pale or stay small, along with stalled growth, point to heavy stress that has gone on for days.
For hot climates, start with the plant itself. Seed catalogs often mark heat-tolerant varieties, and local growers can tell you which jalapeño types keep producing through summer.
Why Flowers Fall Off in Heat and Cold
Pepper plants often drop their flowers when daytime temperatures go above about 95°F or nights fall below about 60°F.18Sandia Seed Company. Pepper Plant has Flowers but No Peppers Pepper pollen can become sterile outside that range, so flowers may not be fertilized.19Sandia Seed Company. Pepper Plant has Flowers but No Peppers Long heat above the comfort zone, especially with warm nights, raises the risk of flower drop.20Pepper Joe’s. Why Are My Pepper Flowers Falling Off: Causes & Solutions
Dropped flowers are not a sign that the plant is dying. It keeps making new buds, and the dropping stops once temperatures return to the comfortable range. Peppers usually start setting again within a couple of weeks of normal weather. In hot regions, a summer lull followed by a heavy fall crop is a familiar pattern, so keep the plants alive and watered through the slow stretch.
Before blaming temperature, rule out other causes. Very uneven watering, such as long dry spells followed by soaking, can stress the plant enough to drop buds. Too much nitrogen fertilizer pushes lush leaves at the expense of flowers and fruit, so a big green plant with few peppers may be overfed. Peppers largely pollinate themselves, so a lack of bees is rarely the main reason, though a breeze or a gentle shake of the plant can help pollen move. Timing is a useful clue: if the dropping lines up with a hot or cold spell, temperature is a likely cause, but if it happens in mild weather, look at water and fertilizer.
Sunscald on Jalapeño Fruit
Sunscald is a burn on pepper fruit caused by the combination of high heat and intense direct sunlight.21Acta Horticulturae. Jalapeno Plant Temperature Tolerance: Cold and Heat Limits Pepper fruit gets injured once its own temperature reaches about 105 to 109°F.22Scientia Horticulturae. Light is essential for sunscald induction in cucumber and pepper fruits, whereas heat conditioning provides protection Heat alone doesn’t do it: without light, hot fruit don’t bleach.23Scientia Horticulturae. Light is essential for sunscald induction in cucumber and pepper fruits, whereas heat conditioning provides protection Fruit hanging in the sun, without leaf cover, is the most at risk.
Scalded spots start out pale or whitish and then turn papery and thin. They most often appear on the side of the pepper that faces the afternoon sun. The damaged patch can later rot or grow mold, so pick the pepper before it breaks down. If the damage is limited and there is no rot or mold, cut away the bad part, and the rest of the pepper is safe to eat.
Prevention is mostly about keeping leaves over the fruit. Avoid heavy pruning that strips the leaves shading the peppers. Shade cloth during the hottest weeks lowers both fruit temperature and light, and staking or caging keeps plants upright so the leaves stay where they belong.
How to Protect Jalapeños From Cold and Heat
High tunnels, simple plastic-covered hoop houses, protect jalapeños from freezing, hail and strong wind.24HortScience. Yields, Fruit Quality, and Water Use in a Jalapeno Pepper and Tomatoes under Open Field and High-tunnel Production Systems in the Texas High Plains A small hoop or row cover over a bed can extend the season in spring and fall.
The night before a frost or cold snap, water the soil during the day, because moist soil holds and releases more heat overnight than dry soil. Cover plants late in the day with frost cloth or sheets that reach the ground to trap soil heat. Avoid plastic that touches the leaves, since leaves can freeze where it touches them. Potted plants are easiest to protect by moving them into a garage or indoors. Take the covers off the next morning so the plants don’t overheat once the sun comes up.
During a heat wave, water deeply in the morning rather than lightly at midday. Mulch the soil to keep roots cooler and moister. Use 30 to 50% shade cloth over the hottest afternoon hours, and move pots off hot pavement or onto a shaded side.
Not every heat remedy works. A white clay spray sold as plant sunscreen had no effect on pepper leaf temperature or yield,25HortScience. Kaolin-based Particle Film Has No Effect on Physiological Measurements, Disease Incidence or Yield in Peppers so spend your effort on water, mulch and shade instead.
Does Hot Weather Make Jalapeños Spicier
Higher growing temperatures raise the amount of the compound that makes chiles hot in many pepper types, though some varieties respond in the opposite way.26PubMed Central. The Influence of Different Factors on the Metabolism of Capsaicinoids in Pepper (Capsicum annuum L.) Peppers grown under stressful conditions also show far more variation in heat, with some becoming much hotter.27JSFA reports. Note on pepper pungency and environmental stress
In your garden, a hot, dry summer can bring spicier fruit from the same plant that gave milder peppers in a cool, wet year. Steady watering and moderate weather usually produce milder peppers. Later fruits can taste different from early ones as the weather shifts across the season. Stress can make peppers hotter, but it also costs flowers and yield, so deliberately starving a plant of water for spice is a poor trade.
The Best Temperature for Storing Picked Jalapeños
About 45°F is the best storage temperature for chile peppers, keeping them for 3 to 5 weeks.28UC Davis Postharvest Technology Center. Chile Pepper Fact Sheet Above 45°F they lose water, shrivel, change color and decay faster.29UC Davis Postharvest Technology Center. Chile Pepper Fact Sheet At about 41°F they keep at least 2 weeks without visible cold damage, but after 2 to 3 weeks at that temperature, seeds start to discolor.30UC Davis Postharvest Technology Center. Chile Pepper Fact Sheet
Too cold causes pitting. Jalapeños stored at about 36°F develop pitted skin after 12 days, whether green or red.31HortScience. Chilling Injury of Chile Peppers (Capsicum annuum L.) Even at about 45°F, jalapeños begin to pit after about 16 days.32HortScience. Chilling Injury of Chile Peppers (Capsicum annuum L.) Signs of cold-damaged peppers include pitting, discolored seeds, softening and decay.33UC Davis Postharvest Technology Center. Chile Pepper Fact Sheet For long storage, freezing is better than a too-cold fridge, if you accept a softer texture. Frozen peppers turn soft after thawing, so use them in cooked dishes, salsas or sauces rather than raw.
Most home fridges run near 37°F, colder than ideal. The crisper drawer or door is often a little warmer. Use fridge-stored peppers within about two weeks, and keep them dry in a loosely closed bag to limit shriveling.