As we approach the 4th of July, we wondered about the history of the saying “Knee-high by the 4th of July” for corn and evaluate if it is still valid.

What is the history of this saying?

According to a 2016 Bayer Crop Science article,

Knee high by the 4th of July” – indicates an important benchmark for growers to determine if they have a good corn crop.

So is this corn growth benchmark still valid?

 “Genetic improvements in corn over the years and earlier planting mean that often corn can be much taller than “knee high” by early July, but the adage is still a good general rule of thumb.”

Some of the genetic improvements include more stress tolerant varieties which allow the corn to grow in dry or wet periods as well as cool and hot periods. These improvements have allowed corn to be grown outside of the traditional Corn Belt areas.  According to Wikipedia, the traditional Corn Belt states include: “Iowa, Illinois, Indiana, southern Michigan, western Ohio, eastern Nebraska, eastern Kansas, southern Minnesota, parts of Missouri and sometimes include: South Dakota, North Dakota, all of Ohio, Wisconsin, all of Michigan, and Kentucky.”

In looking at the 2016 USDA Corn Grain map harvested by an individual county (shown below), corn is now grown in cluster regions in the Southern Plains, Mid-Atlantic, and even the Northeast.

With Corn being grown in other “non-traditional” states and climate regimes, the phrase “knee-high by the 4th of July” is no longer the best rule of thumb for evaluating the health of your corn crop.

For example in my area in Southeast Oklahoma and Northeast Texas the corn, is well over 6 ft.

Picture of corn fields on June 30th, 2017 just east of Paris, TX


In comparison, below is a picture of the corn in the Corn Belt of Illinois. The corn is farther behind in development. 

Cornfields on July 3, 2017, near Campaign, IL.


Finally, below is a picture from Treasured Haven Farms One of our clients in East Central Minnesota. They did not plant the corn until June 1; so it is actually knee high.

Corn in east central Minnesota on July 3rd, 2017.

Is there a more scientific way to evaluate corn growth?

Instead of this general rule of thumb, farmers can use Growing Degree Day (GDD) calculations or also referred to as Growing Degree Units (GDU) to track corn growth. GDD evaluates how the air temperatures influence crop growth. Corn is a well-studied crop with established correlations between corn stages and GDD ranges. The traditional USDA calculations for GDD starts on April 1. However, depending on spring temperature, snow thaws, and field moisture, farmers may not be able to plant their corn by April 1, especially in northern climates. Thus, in addition to traditional GDD calculations, the different planting times and thus corn emergence dates will are also a factor in corn growth. The graphic below shows the stages of corn growth. has more information about the correlations of corn stages and GDD.  

WxIntegrations is developing general GDD information as well as crop-specific GDD values for our GrowCaster product. In addition to this season so far accumulated GDD total, we are developing a forecast GDD value that will include weather forecast information vs climate information. Farmers will be able to use our Forecast GDD values in their planning activities which may include timely applications of herbicides and fungicides as well as irrigation schedules and harvest planning.  We are also looking at strategies to allow farmers to specify a plant date to allow for hyper-customized GDD calculations for their specific farm, crop, and even field.

Our Promise

The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response. 

Our GrowCasterTM tool is the essential weather decision tool for farmers and ranchers that is tailored to their specific farming and ranching operations. With GrowCasterTM, farmers and ranchers can leverage the weather forecast opportunities and risks to improve their bottom line. Register for our  FREE TRIAL today.

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