There are a number of possible reasons for this, including too cool or too warm temperatures, too little or too much fertilizer, too little water or not enough sun. A very common cause of this is that the container is too small, or the plants are overcrowded. In our trials we have found that the smallest container that will produce good quality corn is 24 inches in diameter and depth, with nine plants. Smaller containers or too many plants will cause nutrient deficiencies and water stress because of the restricted space.
You can send us pictures of the plant to the horticulturalist at email@example.com.