Fifty years ago, during the 1974 growing season, many Minnesota farmers were anxious to see how newly released corn hybrids which had been bred to resist southern corn leaf blight might do in our Minnesota climate. After planting, most crops suffered from slow growth and development, as temperatures were cooler than normal during most of the growing season. By August, many farmers were concerned about the potential of frost damage on corn and soybean crops before they fully matured.

Their fears were legitimated by a strong downturn in daily temperatures that started on Aug. 23 and carried on throughout the run of the Minnesota State Fair. On the morning of Sept. 1, the first season-ending frosts occurred in Sherburne, Todd, Hubbard, Wilkin, Polk, Kittson, Scott, and Goodhue counties, where farmers reported damage to crops.

Sixteen more agricultural counties reported killing frost on Sept. 3-4, with morning lows in the low- to mid-20s degrees F reported from a number of places. It was a record-setting 22 degrees at Pipestone, 26 degrees at Montevideo and 27 degrees at St. Cloud. Reports of crop damage (yellowing or dropped leaves) were even more widespread across southern and western portions of the state.

Rebound before the fall

Temperatures rebounded to near normal after those extremely early frosts, but then widespread frosts returned Sept.13-15, affecting 13 more counties mostly in eastern and central Minnesota. Then record-setting low temperatures returned over Sept. 22-23, blanketing the state with lows in the teens and twenties. It was as cold as 10 degrees in St. Louis County and just 19 degrees at Willmar in Kandiyohi County.

With these multiple frosts, the growing season was brought to an end over 95% of the state, so the additional frosts of Sept. 28-30 were rendered irrelevant.

In the end, the growing season of 1974 was one of the shortest in history. The crops suffering frost damage were harvested primarily in a cool and dry early October. The dryness combined with the frost damage kept the moisture content of the crops at harvest time well below normal, so farmers did not need to spend much on drying costs before storing their crops.

Overall, corn yields were low, often 30 bushels per acre or less than the previous year, while soybean yields were 8-10 bushels per acre lower than the previous year, causing a harsh financial blow to farmers.

No recurrence

Thankfully, since 1974 there has been no month of September to match both the earliness and the frequency of frosts. In fact, quite the opposite climate pattern has prevailed, with most agricultural counties in Minnesota recording later and later autumn frosts, often extending the growing season well into October.

More on Minnesota’s weather history is available in my book, Minnesota Weather Almanac: Second Edition, available at most bookstores or through the Minnesota Historical Society Press.

Seeley is an Extension professor emeritus of meteorology and climatology at the University of Minnesota.