Agronomy • 2021-04-12

Early Corn Planting Decisions

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Soil temperature of at least 50º F (10º C) at 2-inch depth and preferably a warming trend in the 3 to 5 day forecast

Germination and root development will not occur below 50º F (10º C) (root growth will be extremely slow even in the low 50's).
Prolonged exposure to low temperatures reduces seed and plant metabolism and vigor and increases sensitivity to herbicides and seedling blights.
The risk of chilling injury decreases incrementally as the soil temperature increases above 50º F (10º C) during the initial imbibition (water uptake).
Sustained temperatures of 20º to 25º F (-7 to -4º C) or below can penetrate the soil enough to damage the coleoptile, mesocotyl, or the growing point and cause plant death in seedlings that haven’t emerged from the soil.

Figure 1. Prolonged exposure to soil temperatures below 50º F (10º C) promotes seed deterioration and seedling disease.

Soil temperature at planting is a key environmental component of stand establishment; however, soil conditions after planting are also critical.

Minimum of 24-hours of rain-free following planting

When a dry seed imbibes cold water (typically 50º F (10º C) or below), imbibitional chilling injury may result (causing cork-screwed shoots, fused coleoptiles, premature leaf emergence underground, and other germination oddities).
Cold water can also cause cell walls in the germinating seed to rupture. Ruptured cells can have ill-effects on developing seedlings and can also attract disease pathogens and insects.

Figure 2. Coleoptile injury from freezing temperatures

Avoid planting right before a period of large temperature swings

Even if the “average” soil temperatures are above optimum, seedlings can be adversely affected by wide swings in soil temperatures. Affected seedlings will have stunted and distorted leaves and may or may not emerge from the soil..
Research has shown that a swing of soil temperatures of more than 27º F (-3º C) (soil high temperature minus soil low temperature > 27º F) may adversely affect mesocotyl growth.
Sandier soils can often be planted earlier in the spring because they dry out faster than heavier soils; however, sandy soils tend to experience wider temperature fluctuations, especially on clear nights with cold air temperatures.
The effect of adverse conditions can and does vary from seedling to seedling, causing erratic and uneven stands.

Figure 3. Cold-temperature induced “corkscrew” damage symptoms.