Corn Plants Turning Yellow

Roasted ears of golden corn (Zea mays) straight from the grill tickle the palate and announce the beginning of barbecue season for millions of Americans. So much so, that home gardeners across the United States plant sweet corn with the hopes of producing plump, juicy ears just right for the grill. Under normal circumstances, when planted in fertile, well-drained soil in a sunny location, corn seeds germinate quickly and produce lush, green, grass-like leaves. Sometimes, however, things go wrong and corn leaves turn a sickly yellow.

Corn prefers a soil pH between 6.0 and 6.8 and suffers when the pH falls below 6.0. This causes yellowing of the leaf edges and uneven stands of corn. A gaze down the row may reveal corn plants at varying heights. Some leaves may appear purplish with yellow edges. To correct problems with low pH, test your soil before planting and apply ground limestone to raise the pH of the soil. The amount of limestone needed depends on your soil's pH and the structure of your soil.

Many gardeners automatically assume that yellowed foliage in corn is the result of a nitrogen deficiency. Although this may be the cause of your yellowed corn, it is not the only deficiency that causes yellowing. A sulfur deficiency often causes yellowing of new leaves, while the older leaves remain green. A potassium deficiency typically appears as corn approaches the knee-high stage. Older leaves develop yellow margins while new leaves are green. A nitrogen deficiency presents as yellowing of the entire plant.

Cold weather and cold, wet soils also cause yellowing in corn. Both may cause the entire plant to be stunted and yellow. This often corrects itself as the weather improves and the soil dries. If you observe yellowing of your corn foliage early in the season before the weather warms sufficiently for this sun-loving veggie, waiting a few weeks until the weather improves is key to solving the yellowed foliage.

All plants need adequate sunshine to photosynthesize and make chlorophyll, the green coloration found in plants. Corn is no exception. It requires at least six to eight hours of direct sunlight a day and performs best in all-day sun. A lack of sun may cause your corn leaves to appear pale green or yellow.

Testing your soil in the fall or in the spring before planting allows you to assess and adjust nutrient levels and soil pH before planting your corn. Adding copious amounts of organic matter, such as compost or well-rotted manure, to the soil improves aeration and drainage, both of which play a role in problems with cold, wet soil. Other options include covering the soil with black plastic two weeks before planting to warm the soil or delaying planting corn until the weather and soil warms sufficiently. Side dressing your corn with ammonium nitrate or nitrate of soda, at a rate of 1 tablespoon per hill, when the corn is 18 inches high, replaces the nitrogen corn uses from the soil.