Cool weather in Indiana a sign of frost, freeze soon?

September 22, 2011

This Indiana map shows the average first date of temperatures below 32 degrees Fahrenheit by county, based on a historical analysis by the State Climate Office. (Indiana State Climate Office graphic)

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WEST LAFAYETTE, Ind. – With unseasonably cool weather in Indiana lately, a question farmers and home gardeners might be asking is when they will get their first freeze or frost.

The answer depends on where they live. But here's what they can expect based on an analysis of historical temperatures by the Indiana State Climate Office, based at Purdue University:

* Temperatures in Indiana typically have not fallen to the freezing point of 32 degrees Fahrenheit before Sept. 23, the first day of autumn this year. There is only a 10 percent chance of that happening.

* For most of the state, the first freeze has come during the five days of Oct. 12-16. The average date is two weeks later along the Ohio River in the south, where it is naturally warmer, and along Lake Michigan in the north, where the lake is warmer than land this time of year.

* It's a near certainty – a 90 percent chance – that most of Indiana will have its first freeze by Oct. 31.

Last year, freeze dates across Indiana ranged from Oct. 4 to Nov. 6.

For some farmers who were delayed in planting corn and soybeans, there is a risk that the crops will not mature before an early killing fall freeze.

As of Sept. 18, about 36 percent of the Indiana crop was mature and in no danger from yield loss, said Purdue Extension corn specialist Bob Nielsen. But plants not mature by the time of frost or freeze can be damaged or die.

Frost, which can occur at temperatures above 32 degrees, can damage the leaves of immature corn and result in some yield loss. But the loss would not be as large as that from plants exposed to temperatures of 28 degrees or lower for several hours, Nielsen said.  

"Corn plants exposed to such temperatures will usually die completely, and the yield loss of an immature crop is much more dramatic than a simple frost that kills leaves," he said. "The significance of an early occurring fall frost or freeze event should not be underestimated."

About 39 percent of the Indiana soybean crop began to mature as of Sept. 18 and would reach maturity in 10-14 days, said soybean Extension specialist Shaun Casteel. It could be harvested five to 10 days after that given good drying weather. The remaining 60 percent would mature and be harvested beginning in mid-October.

Frost and freeze generally are not a problem for commercial fruit and vegetable growers because most harvests are completed before then and growers routinely use established protection methods.

Some gardeners might be interested in trying to protect tender vegetable crops or bedding flowers when frost is predicted, taking advantage of a few weeks of good growing weather that often follows, said Rosie Lerner, Extension consumer horticulture specialist.

Lerner offers advice on how to protect plants from an early frost in an online column at http://www.hort.purdue.edu/ext/avoidfrost.html 

Writer: Keith Robinson, 765-494-2722, robins89@purdue.edu

Sources:  Indiana State Climate Office, 765-494-6574, iclimate@purdue.edu

  Bob Nielsen, 765-494-4802, rnielsen@purdue.edu

  Shaun Casteel, 765-494-0989, scasteel@purdue.edu

  Rosie Lerner, 765 494-1311, rosie@purdue.edu

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
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