Corn is a tropical grass domesticated in the Americas, and its physiology is inherently adapted to warm environments. Because of this warm-weather origin, the plant is highly sensitive to cold. Determining the lowest temperature corn can survive is complex, depending on its specific growth stage and the duration of cold exposure. Understanding these limits is important for agricultural planting decisions, as the plant’s ability to withstand cold changes drastically from a newly planted seed to an established stalk.
Temperature Requirements for Seed Germination
The first cold temperature challenge corn faces is the soil, which must be warm enough for germination. The minimum soil temperature required for a corn seed to successfully sprout is approximately 50°F (10°C), measured at the planting depth. While the seed may remain dormant in colder soil, growth will be extremely slow, delaying emergence and increasing vulnerability to soil-borne pathogens and insects.
For rapid and uniform emergence, the optimal soil temperature range is significantly higher, generally between 60°F and 70°F. Planting into cold soil risks imbibitional chilling injury, or cold shock. This injury occurs if the seed absorbs water below 50°F during the first 24 to 48 hours after planting.
During this initial phase, the dry seed rapidly takes in water to rehydrate its cells and start metabolism. If the water is too cold, the cell membranes within the seed can fail to reorganize properly or may even rupture during the rapid swelling process. This cellular failure often results in a non-viable kernel or a seedling with stunted structures, ultimately leading to a lost plant stand.
The Critical Threshold for Corn Seedlings (V0-V4 Stage)
Once the corn plant emerges (V0-V4 stage), it is highly susceptible to cold air temperatures, but it possesses a built-in defense mechanism. The growing point, the region where all new tissue originates, remains protected below the soil surface until approximately the V5 or V6 growth stage.
This protected growing point means the plant can often survive a mild frost that kills all the above-ground leaf tissue. However, the absolute lowest air temperature that kills the entire seedling is generally 28°F (-2°C) or colder, especially if sustained for several hours. Temperatures at this level can penetrate the soil surface, causing the lethal freezing of the growing point itself.
The susceptibility of the growing point is exacerbated by dry soil, which lacks the thermal buffering capacity of moist soil. If the growing point is damaged, the plant cannot produce new leaves and will die. This makes the duration of the cold event and the soil conditions just as important as the minimum temperature reached.
Tolerance of Established Corn Plants (V5 and Beyond)
The cold tolerance dynamics of corn change significantly once the plant reaches the V5 stage. At this point, the growing point begins to elevate above the soil surface, making the plant fully susceptible to freezing air temperatures. The protective mechanism that shielded the seedling is lost, and the plant’s survival hinges entirely on the air temperature.
Established plants are killed when the air temperature drops to the lethal threshold of 28°F or lower, a temperature range that can freeze the now-exposed growing point. Temperatures that remain below 32°F for four to five hours are also sufficient to cause substantial damage to all above-ground tissue, including stalks and husks. The severity of damage at this stage is more immediate and comprehensive because the entire stem apex is exposed.
Later in the season, just before harvest, a hard frost can kill all leaf tissue and stop the grain-filling process. The plant does not gain any increased cold tolerance as it matures; instead, the consequences of tissue death shift from stand loss to yield loss. The loss of leaves at this later stage prevents further photosynthesis and dry matter accumulation in the developing kernels.
Physiological Damage Caused by Frost
The visible damage caused by cold temperatures is a direct result of cellular destruction. When air temperatures drop below freezing, ice crystals form within the plant’s cells or in the spaces between them. The formation of these crystals physically ruptures the cell membranes, leading to the rapid death of the tissue.
The immediate symptom of this cellular breakdown is a water-soaked or dark, blackened appearance on the leaves within the first 24 hours after the frost event. This dark discoloration is followed by the tissue drying out and turning brown or necrotic over the next few days.
In contrast, non-freezing cold temperatures, typically below 50°F but above 32°F, cause chilling injury. This cold stress does not immediately kill the tissue but slows down metabolic processes, leading to stunted growth, yellowing, and poor vigor. This chilling can also predispose the plant to other issues, such as disease.