The Midwestern Regional Climate Center, based at Purdue University, recently released a freeze date tool. It makes it easy to find historical temperature information that may help growers plan.
Liz Maynard, Purdue Extension vegetable production specialist, recently reported that the new tool makes it easy to find information about average first fall frost and last spring frost dates, and the frost-free growing season between them for your particular county in the Midwest or Northeast, as well as across the entire region. The tool covers counties in 25 states.
“One feature of this tool that could make it especially useful for fall crop and high tunnel production is that you can choose temperatures below 28°F,” she said. “First/last freeze dates have in the past typically been reported for 36°F, 32°F, and 28°F, which is useful for warm season vegetable crops in the field.” For cool season and high tunnel crops, dates of colder temperatures are relevant, she said.
“For example, row covers are often applied over winter crops in unheated tunnels when external temperatures drop below 25°F, and some producers add a second cover when temperatures go below 20°F,” she said.
The need for supplemental heat in a high tunnel also depends on outside temperature. “For example, row covers should be enough to protect a new tomato crop planted early in spring in an unheated high tunnel when the temperature drops below 32°F outside, but if it gets to 20°F supplemental heat would be needed,” she said. “Of course, day-to-day decisions will be made based on the current conditions, but the historical trends help in planning.” Maynard added that knowing typical dates for colder temperatures can also help in predicting when less hardy cool season crops (e.g. lettuce, Swiss chard) are likely to be killed or become unmarketable.
The information in the tool is based on data from 1950-2021. You can find dates for each decade separately by choosing the ‘Trend Map’ option, clicking on the county of interest, and choosing ‘Freezes by Decade.’
“I expect it to prove useful for vegetable growers in a variety of ways,” she said. “Some uses will probably be immediate; others will take more time, research, and communication among growers, Extension, and researchers.”
Find the tool online at: https://mrcc.purdue.edu/freeze/freezedatetool.html. Find Maynard’s original article at: https://vegcropshotline.org/.