This Outlook Brief leverages The Climate Corporation’s extensive database of historical weather and agriculture data to analyze the early fall freeze risk that growers should consider when deciding whether or not to double crop soybeans this year.
An extremely warm spring has led to a near-record development pace for the US winter wheat crop. According to the USDA, 48% of the US winter wheat crop had been harvested as of June 17th, well ahead of the 16% harvested pace that the crop has averaged by this date over the past 5 years. 
The early harvest of winter wheat this year is presenting growers around the country with an opportunity to double-crop soybeans (double cropping is a farming practice where a grower harvests two different crops from the same field in the same calendar year). While it is fairly common to double-crop soybeans after wheat in southern regions of the United States where the growing season is longer, it is much less common to double-crop in northern latitudes where the growing season is shorter. In these regions there is typically not enough time for a second crop—planted after the harvest of the winter wheat crop – to get to full maturity before the first killing freeze of the fall.
As one example of just how unusual 2012 conditions are, the University of Wisconsin recently put out a paper discussing the potential profitability of double crop soybeans in Wisconsin this year.  The paper cites the fact that the winter wheat crop is three weeks ahead of schedule in development compared to 2011 and that, though it is risky, there is a “potential profit for Wisconsin growers to double-crop soybeans in 2012.” One of the main risks to planting double crop soybeans in Wisconsin, and many other locations this year, is the chance that an early fall freeze will kill the plant before sufficient yield is realized for the second crop to be profitable.
To help growers understand the early freeze risk that they will face when planting double crop soybeans this year, The Climate Corporation has created a First Freeze Date table that shows the earliest and median first freeze date for almost 1,000 different locations across 12 Midwestern states. The full data table is available in the appendix of this report and a graphical representation of the data can be seen in the figures below. The data includes:
Analyses of both 30 and 28 degree Fahrenheit freeze dates were performed to allow growers to assess the risk of partial freeze damage vs. hard freeze damage. In a typical situation, soybeans would be expected to take some damage to the tops of the plant if and when temperatures fall to 30 degrees Fahrenheit, but much more significant damage - up to total plant death - can be expected when a hard freeze occurs and temperatures drop to 28 degrees or lower . In all cases, the length of freeze is important, with longer freeze events leading to greater damage than shorter freeze events.
As seen in Figures 1-4, it is important to consider microclimates when using the data found in the appendix. The temperature stations included in this analysis report data that is representative of the immediate area where the weather station is sited. As one example, you can see that the weather stations on the shores of the Great Lakes generally report much later first freeze and median freeze dates than the other weather stations in the immediate vicinity that are further inland. This is because their proximity to the large body of water keeps the immediate area warmer at night than areas that are even just a few miles further inland.
Growers can use the data in the appendix to see both the ‘worst case scenario’ they might expect to see at their location—the earliest freeze date their area has experienced in the last 32 years—and also the median freeze date for their location over the last 32 years. The median freeze date is the date where exactly half of the 32 historical years have seen their first freeze happen before that date and half of the historical years have seen their first freeze happen after that date. Absent any deviation from the historical weather patterns, it would require an unusually warm fall for the first freeze at any given location to happen after the listed median freeze date for that location.