This catchy phrase is actually quite useful. In previous decades, the height of the corn would suggest the degree of crop success. Ideally, corn would be chest-high by the Fourth, but if the corn was not at least knee-high on the nation’s birthday it meant the crop was struggling and may not be ready in time for harvest. On farms today, this model has outlived its accuracy. Better understanding and selection of seed genetics have given farmers opportunity to succeed no matter what their position is on the Fourth.
Advances in seed genetic research and selection have produced seeds with better plant vigor, disease resistance, and growth efficiency. This is true for both organic and conventional seeds. These modern corn varieties have allowed crops to flourish in conditions that may have stunted or destroyed past generations. So even in dry or wet times, hot or cool, the crop will continue to grow and flourish. In ideal growing conditions, corn crops can be taller than previously recorded. In parts of Iowa, corn fields can measure as high as six feet tall by our Independence Day. Even when the corn is stunted, it does not imply that the crop is doomed. Often times, the genetic integrity of the crop will still kick in and produce a sufficient harvest in fall.
The improvements have also changed when farmers choose to plant their crops. Corn crops were usually planted late May to make sure that soil temperatures and weather supported germination and early plant growth. Genetics have allowed corn crops to be planted in mid to late April resulting in a longer growing season and hopefully a higher harvest yield. Earlier planted corn will usually super succeed the knee high by the Fourth of July “rule”.
This year, Silver Reef Organic Farms had a late start. Due to late snows and significant May rains, our fields were too wet to plant on time. While other farmers in our area started in April, we didn’t start planting until late May. We were worried that our corn crop would be behind but we honestly had nothing to worry about. Even though we planted in late May and only had about six weeks of growth, our corn was almost 3 feet tall at Independence Day. The corn had a shorter growing interval but still succeeded to being “knee high.”