Knee-High by the 4th of July

Once considered a good omen for a high-yielding crop, the folksy phrase “knee-high by the Fourth of July” would likely be taken as an insult or a sign of trouble in today’s fields.

Typically, South Dakota corn crops will be much taller than knee-high by this patriotic holiday; probably closer to waist-, shoulder- or even head-high, depending on your height, of course.


Just for fun, many corn farmers across the state, and the whole country, will likely be sharing photos on social media of their kids standing in the cornfield this Fourth of July weekend. The photos will show how much taller the corn is compared to “knee-high” on a photogenic child.

Some have said this measuring-stick mantra actually dates further back in time so that the ruler relies on the height of a man’s knees when riding horseback in the field — obviously estimating the average heights of a horse and a man. Oddly enough, that very scene is the source of another whimsical line related to the height of a growing corn crop.


As the popular 1943 musical Oklahoma! (and 1955 film) opens, lead movie actor Gordon MacRae, playing lovesick Curly McLain, rides a horse at the edge of a cornfield on his way to visit the farm of his secret love, Laurey Williams.

In the first song, “Oh, What a Beautiful Mornin’”, he croons this now-famous line about corn height: “The corn is as high as an elephant's eye, An' it looks like its climbin' clear up to the sky.”

“The corn is as high as an elephant’s eye” is closer to accurate, although not as easy to prove, unless you own an elephant, that is. No one is quite sure why an elephant was used as a comparison in calculating corn crop heights back then, but it was likely due to creative license (and the need to rhyme with sky) by the song’s well-known creators, composer Richard Rodgers and lyricist Oscar Hammerstein II.

DYK: An average adult African bush/savanna elephant is approximately 10-13 feet tall, making their eyes at about the 9-11-foot mark. A smaller Asian elephant typically stands around 8 feet tall. It’s unclear which type of elephant the lyric-writers intended. Source: The Aspinall Foundation.


No matter which animal or historical measuring tool you choose, corn currently growing across South Dakota should be quite tall at this point in its season.

Unfortunately, this year’s challenging conditions of #Drought21 with too little rainfall have held back the crop’s development and have already affected its yield potential.

Right now across our state, corn plants are likely in the 14-Leaf (V14) stage of rapid growth, which is also when it’s very sensitive to heat and drought stress. This is when it puts on extra leaves and reaches its full height.

Next, a tassel sprouts from the very top, completing the 6-step vegetative stage, and the plant moves into the 6-step reproductive stage from silking (flowering) to maturity and finally harvest. See a detailed illustration of corn growth and development here.

DYK: Unlike field corn, the sweet corn we eat is just a mere 1% of the total harvested here in America. Almost all (99%) of the corn crop is field or dent corn that becomes animal feed, ethanol fuel, and ingredients used in industrial food products such as high-fructose corn syrup, corn oil, corn starch, plastics and much more.


For more than 75 years, seed genetics have advanced corn varieties and hybrids far beyond the origins of this grass-based plant known as teosinte in Mexico some 9,000 years ago.

Maize (Zea mays), or corn as it’s commonly called, has been domesticated and developed into an essential crop across the world that helps feed and fuel the global population. For more background into the history of corn, click here.

Some of the earlier methods of growing corn look nothing like how it’s done today in vast fields of perfectly aligned rows that are planted with wide-working, high-tech seeding equipment.

The ancient “milpa” or “Three Sisters” method was used by the Iroquois to plant corn, beans, and squash together by hand more than 300 years before European settlers arrived in America. We featured this “chaos garden” style of growing vegetables in a previous blog post. Read all about it here.

DYK: Since 1940, total acres of corn planted in the U.S. has remained relatively steady, yet the number of bushels harvested (yield) has grown more than 6 times that of those early harvests. [Click the charts to see them larger.] 


It’s estimated that 60% or more of the yield gain growth was due to improved seed genetics, not advances in machinery or other crop inputs. Technically, the term “precision ag” typically relates to the equipment used, such as high-tech tractors, global positioning systems, variable-rate applications, and such.

Because hybrids are “engineered” through inbreeding and trait selection science to boost uniformity and yields, the seeds themselves could also be considered “precision ag.” In addition to enhancing the plant’s ability to produce, it also helps defend it from disease, weeds and pests, not to mention drought.


Without doing a deep-dive into the science, the chart shows how the types of corn genetics — open-pollinated, double-cross and single-cross — have helped raise yields. Around 1940, the first hybrid seed corn (double cross) was introduced. Note the sharp rise following that decade.

DYK: Current corn hybrids can achieve up to 13-foot heights. They typically reach upwards of 10 feet at full maturity.


While height has historically been a marker of future yield success, new advances in seed engineering are leading to shorter hybrid development. Why would this be of interest? Taller stalks can suffer from damage from drought and wind, sometimes snapping off from the weight of the ear being grown.

Short-stature corn is more physically stout to withstand wind and can focus the plant’s energy on developing ears rather than growing the plant taller. Dwarf traits are not new but are growing in popularity. Stalk standability becomes a much bigger concern in extreme winds such as the derecho that destroyed a large swath of corn production across central Iowa and Illinois.

Another advantage of shorter corn is that it could be sprayed later in the season to prevent pests or disease damage, or even to fertilize for a yield boost. Lower-height corn allows sprayers and application equipment to make a later pass over the crop.

Bayer is developing a short stature corn similar to VITALA, a variety recently launched in Mexico that only reaches a maximum height of 7 feet tall. These scientific advances offer promising solutions to our growing concerns for climate change with extreme weather threatening our food supply as our planet's demand only grows with population.


It’s hard to say which direction the industry will go for sure in the future, but one thing is certain: science will be leading the way to help our farmers grow a better and bigger corn crop more efficiently and economically. That’s the beauty of seed genetics.

Maybe a new phrase about corn height will become popular. Until then, you’ll know that “knee-high by the Fourth of July” is under-estimating most of our country’s corn crop. And that corn “as high as an elephant’s eye” is closer to reality…for now.

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