Growing up on an Iowa farm in the 1980s + 1990s, a common phrase was that the corn crop should be a knee high by the fourth of July. I don't have a clear recollection on how often that was accurate, but my memory over the past 20 years or so have shown it to be a vast under-estimation of corn height for the date. The featured chart presents some NASS estimates of percentage of Iowa corn crop that has reached silking stage by the day of the year. This stage would indicate a corn crop that is taller than most humans! The just released weekly update had 4% of Iowa's crop at such a stage on Sunday. The 4% value is denoted by a "X" on each of the previous years. This year's value one of the earliest on record, but not too far ahead of a recent average. The plot does show some NASS reporting differences with more limited early season reporting back in the 80s and 90s. So such a plot doesn't necessary disprove the old saying, but would certainly hint that having knee high corn on today's date would be very exceptionally late.

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