Corn is a warm-season grass, and its growth depends on warm temperatures, making the crop generally non-tolerant to frost. This sensitivity means early and late-season frost events are a major concern for growers, as freezing temperatures can easily destroy above-ground tissue. The degree of damage sustained depends heavily on two factors: how low the temperature drops and the plant’s exact stage of development. Understanding these specific thresholds and recovery mechanisms is the primary defense against unexpected cold snaps.
Corn’s Critical Temperature Threshold
The temperature that causes damage is close to the freezing point of water, though the duration of exposure is also a factor. Temperatures that dip to \(32^\circ\text{F}\) (\(0^\circ\text{C}\)) for a few hours can be destructive to tender leaf tissue. The threat occurs when the temperature drops to \(28^\circ\text{F}\) (\(-2^\circ\text{C}\)) or lower for even a few minutes, as this can be lethal.
When the air temperature drops below freezing, ice crystals begin to form inside the plant cells and in the spaces between them. This crystallization physically damages the cell membranes, causing the cells to leak their contents and collapse. The extent of this damage determines whether the plant can continue growing or if it will die.
Varying Tolerance by Growth Stage
The corn plant’s ability to survive a frost changes based on the location of its growing point, the area of actively dividing cells that produces new tissues. In the early seedling stages, from emergence (VE) up to the fourth or fifth leaf stage (V4 or V5), the growing point remains protected below the soil surface. Soil acts as an insulator, shielding this area from colder air temperatures.
During this early phase, even if a frost kills all exposed leaves, the plant typically survives and regrows from the protected growing point. Although the plant may appear dead above ground, the meristem is often unharmed and can initiate new growth once temperatures warm. Once the plant reaches the V5 or V6 stage, the growing point begins to rise above the soil surface and is exposed to the elements.
From V6 onward, the corn plant becomes vulnerable, and a hard frost that kills the above-ground tissue will kill the entire plant. Late-season frost, occurring after the grain has reached physiological maturity (indicated by the black layer), will not kill the plant but will accelerate drying and affect grain quality and moisture content. If frost occurs before the black layer forms, it halts grain fill, resulting in lighter, shriveled kernels and reduced yield.
Recognizing and Evaluating Frost Injury
The first visual symptoms of frost damage are typically seen within 24 to 48 hours, including a water-soaked or wilted appearance of the leaves. As the damaged tissue dries, it eventually turns brown or black. The damage may seem severe, but recovery potential hinges entirely on the health of the growing point.
To accurately assess the damage, growers should wait three to five days after the frost event. This delay allows the plant to begin exhibiting signs of recovery or death, as cool weather can slow the visible deterioration of damaged tissue, making an immediate assessment unreliable. To check the growing point, dig up the plant and split the stalk lengthwise.
A healthy growing point will be firm and appear light yellow or white, indicating it is viable and capable of producing new leaves. If the growing point is soft, mushy, or discolored (brown or black), the cell tissue has died, and the plant will not recover. Scouting the field and checking multiple plants across different areas is necessary to determine the overall stand loss.
Protective Measures and Recovery Tactics
The most reliable preventive measure is timing the planting date to avoid the historical window for the last spring frost. Farmers with irrigation can apply water before a predicted frost event. Wet soil absorbs more solar energy during the day and releases heat more efficiently than dry soil overnight, which can slightly raise the temperature near the soil surface, offering protection to young seedlings.
After a frost, the best tactic is patience; avoid making an immediate replant decision. If the growing point is viable, the plant will push out new growth, often appearing twisted or “corkscrewed” as new leaves struggle to emerge from the damaged whorl. Monitoring fields for secondary issues, such as bacterial soft rot, is important, as stressed or injured plants are more susceptible to disease.
New leaves emerging from the whorl after a few days confirm the plant is recovering, despite severe damage to the older leaves. While initial defoliation may slightly delay growth, the long-term effect on yield from losing the first few leaves is minimal. Clipping the dead tissue is discouraged, as research shows it can increase the risk of introducing secondary bacterial infections.