Here we are again, talking about frost in late August- not because there's necessarily a big threat of an early frost, but because crops, particularly corn, are going to need all the time they can get again this year to mature and dry down to reasonable levels. We were in this same boat at this same juncture last year. Mother Nature smiled on Indiana a year ago, for the most part, with enough heat to get crops mature, holding off frost until later than normal. Some areas certainly could have used rain during the period, just like they could right now.
One thing Jim Newman taught students was that there are so many variables that can affect not only if a frost occurs, but how much it affects plants that it's very difficult to predict whether a frost will be early or late in advance. Right now, Dec Niyobi, the Indiana State ag climatologist, says signs point toward a somewhat early frost, but it's really too early to gauge what the impact might be.
Newman, the retired ag climatologist and Purdue Extension agronomist, says such factors as altitude above sea level, type of cover on the ground, hour at which temperature drops, how long it drops, and how frost intertwines with topographical feature sin the area can determine if a frost occurs on a given night. As to whether plants are killed that boils down to how cold it actually gets, and how long it stays at that temperature.
If you're considering frost as 36 degrees, you're going to be talking a much earlier date than someone who considers frost as 32 degrees. In turn, those who say a killing frost is 28 degrees, has an even later date to talk about. There are certainly differences in plants as to how sensitive they are to frost injury and/or death. Tomatoes, for example, are one of the first vegetable plants to show frost injury and succumb to frost as temperatures drop.
Form the Purdue University Corn & Soybean Field Guide, here are just a few average first 32 and first 28 degree reading for selected areas. You can find the complete list in the pocket guide. Note the difference between the two. If a 36 degree frost was also included, it would be earlier than the 32 degree date. These dates are based on averages over a long time period, usually 30 years.
||32 degrees||28 degrees|
|Lawrence||Oct 13||Oct 28|
||Oct 7||Oct 21|
|Orange||Oct 9||Oct 22|
|Parke||Oct 14||Oct 28|
||Oct 13||Oct 24|
|Randolph||Oct 6-13||Oct 19-28|
|Ripley||Oct. 18||Oct 28|
|St. Joseph||Oct 19||Nov 2|
|Tippecanoe||Oct 6-9||Oct 19-21|