As you’re locking in the corn hybrids you will plant on your farm in 2022, maturity comparisons between seed companies may be on your mind. Is the 100-day corn from Company A going to mature at the same time as the 100-day corn hybrid from Company B? If you’re trying to spread your risk out and plan your harvest schedule, it’s helpful to have that comparison. However, seed guides are often quite deceiving when it comes to maturity, and there is no industry standard of measure.

Let’s look at the primary ways hybrid maturity differences are categorized.


It seems pretty straight forward. Counting the growing degree units during the season should be a simple math equation and not controversial at all. It’s not, though. The big question is WHEN do you start counting? Do you count from emergence to black layer? Should you count from planting to black layer instead? It doesn’t seem like a big difference, but when you consider it takes roughly 100 to 120 GDUs for most corn plants to emerge, that could make the same hybrid look like it needs 2650 GDUs when it really needs 2770 GDUs to mature. This is especially important in a late-planted situation where maturing before frost hits is non-negotiable.

The other challenge here is seed companies often only track hybrids for a few seasons before they are put on the market. After that, there is so much data to collect, breeders often spend their time on disease ratings and not necessarily on maturity. In my experience, the proof is evident in the fact that hybrids that have been on the market for two or three years RARELY see their GDU ratings change. So if a hybrid comes out in a cool, cloudy year like 2019 versus during a warm, sunny year like 2021, there is bound to be a difference in how many GDUs it takes for that hybrid to reach black layer.

In summary, GDUs are a flawed method to compare hybrids, but this system is about the best the industry has to offer. In the future, there will be far better ways to account for the time from planting to maturity, including measurements of sunlight and temperature variance throughout the day. Do you think a day that was cloudy and cool until 5 p.m. with a temperature reaching 86 degrees for 5 minutes would push corn hybrids to maturity as well as a day that was 86 degrees for 8 hours and sunny the whole time? Not a chance.

What Does 100-Day Corn Really Mean?

We get this question a lot. What does the “day” scale on hybrids really mean? First of all, 100-day corn doesn’t mature in 100 days exactly every time. If you plant 100-day corn on May 1, it won’t be ready to harvest around the 9th of August. This measurement scale is thought to relate back to when corn hybrids were compared for drydown. The average drydown was about 0.5 points of moisture per day, so if a hybrid came in 2 points wetter than a 100-day hybrid, that would mean it should take four more days of drying at a rate of 0.5 points of moisture per day, making it a 104-day hybrid.

Where Can You Get a Real Answer?

Watch for hybrid comparison trials in your area where the corn gets harvested early at a moisture of 20 to 25 percent. You can really see the differences between hybrids then. If corn gets down to 15 percent moisture and is harvested late, most hybrids look pretty similar.

Also, we really like the Midwestern Regional Climate Center website. You can use your planting date, hybrid information, and historical local weather data to forecast exactly when your hybrid should be mature, along with your odds of beating the first frost.