Temperatures as low as 28 degrees F finally reached central Indiana around October 11 or 12. It was cold enough in many areas, especially low-lying areas, to bring a halt to the growing season for most double-crop soybeans, specially those planted in the more risky regions of the state, nearer to Interstate 70 than Interstate 64.
One farmer near Morgan County made an interesting observation, however. About a day after the cold morning, he noticed that his doublecrop soybeans in a low-lying bottomland field were turning brown prematurely, definitely cooked by frost. For all practical purposes, the growing season was over for them. He wasn't surprised, knowing that it had reached all the way down below freezing in his area.
But back on high ground on a field he had combined a couple weeks earlier, he did find a surprise. There are always a few soybeans left behind, even by the most conscientious person running the most modern combine. Those were sprouted. Many were in the first trifoliate stage.
"They weren't bothered a bit," the farmer says. "They took that cold weather and kept on going. It's going to take lower than 28 degrees F to stop them."
Eventually it will get colder, naturally, and they will succumb. But the farmer was stymied, wondering why the very tiny beans weren't hurt, while the doublecrop bans were nipped, as he expected.
The explanation may lie in the same reason why farmers have successfully been planting soybeans in the spring much earlier than conventional wisdom ever said they could. Young soybean plants can withstand much colder temperatures than anyone ever thought they could up until less than two decades ago.
Nearly two decades ago, Purdue researchers documented that it took temperatures in the mid-20s to kill young seedlings, depending on how long it stayed cold and the exact stage of growth. But the report collected dust in a drawer.
Six years ago Indiana Prairie Farmer and Beck's Hybrids, working jointly with Purdue, conducted cold chamber, replicated tests that produced the same results. Soybeans up to the trifoliate stage could withstand 28 degrees for two hours or more. Sometimes they even survived at 25 degrees. It took 23 to 25 degrees to begin freezing out a significant number of soybeans in any one test sample.
So if you still see soybeans growing where you've combined, don't be surprised. They will die off eventually. But who knows? Maybe it won't be that long after they die off that you decide it's time to put the next crop into the ground?