Farmers are getting anxious about the delays occurring for corn planting this year. Little field work has taken place so far and planting will be further delayed not only in Wisconsin but throughout the U.S. Corn Belt. Research data indicates that the optimum date for corn planting in southern Wisconsin is May 1 and in the north it is May 5.

Since 1979, farmers have started planting (5% planted) between April 22 and May 8 (Figure 1). Half of the acres have been planted between May 5 and May 23. Planting is essentially complete (95% planted) between May 27 and June 18. On average 5% of the acres are planted by April 29, 25% by May 7, 50% by May 13, 75% by May 20, and 95% by June 2. Since 1997 farmers have more consistently started planting earlier (April 22 to April 27) with over half of the acres planted by May 15, except for 2002.

One of the characteristics of record yielding years is earlier than normal planting date. In general, early planting "sets-up" the growing season and may result in higher yields. Record corn yield years have occurred in 1981, 1986, 1991, 1994, 1999, and 2005. Record years had 50% of corn planted by May 15, except for 1991 when it took until May 17 to plant 50% of the acres.

Low yielding years like 1979, 1983, 1993 and 1996 had 50% of acres planted on May 22 or later. An exception was 1988 when 50% of corn acres were planted by May 11. Planting progress was unique in 1988 - it was the shortest planting season measured requiring only 22 days beginning (5%) on May 2 and finishing (95%) on May 24. The longest planting seasons to go from 25% to 75% of the acres planted were 2003 and 1983 requiring 21 to 22 days.

The number of days to plant 50% of the acres (25%-75%) averages about 14 days with the quickest year being 2000 when it took only 9 days. In that year, 3.5 million acres were planted. So, over the 9 day period, 1.75 million acres were planted (200,000 acres per day). This rate is probably the fastest we could plant corn in Wisconsin.

With the exception of extreme high- and low-yielding years, no good relationship is observed between planting progress and grain yield. Above-average yields can still occur even though planting may be delayed. Likewise, lower than average yields can occur even though planting progress is faster than normal. The bottom-line is that there is still a lot of growing season remaining and a lot can happen.

Figure 1. "Candlestick" graph of corn planting progress and grain yield (source: USDA-NASS). The beginning of the bottom "wick" is the date when 5% of Wisconsin corn acres are planted in Wisconsin, the bottom of the "candle" is 25%, the line in the middle of the candle is 50%, the top of the candle is 75%, and the top of the wick is when 95% of corn acres are planted.