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A 'New Normal' for Minnesota's Last Spring Frost Date?

Photo: Julie Weisenhorn, UMN Extension
If you had to name the date, when is the average last frost date for Minnesota? Mid-May sometime, perhaps? One expert says the unofficial data shows it's a lot earlier than you might think!

According to Dr. Mark Seeley, University of Minnesota professor emeritus and meteorologist, we can expect new normals in the last spring frost date for Minnesota. In his March 29th program on MPR Weather Talk radio, Dr. Seeley said in the last 20 years, April 20th was the average date for the last frost! 

When I spoke with him by phone recently, Dr. Seeley said,  “Since 1999, we have only had two last spring frosts in May, the rest have all been in April. The latest was May 9, 2010 and the earliest was April 8, 2006.”

Data becomes official in 1-2 years

The years 2019-2020 still need to be added to the new historical data (1991-2020) that will come out in late 2020 or 2021, but “for now we can see that the new median spring last frost date is shifting much closer to April 20.” This is of great interest to gardeners, who are anxious to begin planting.

What are the chances for a May frost?

Current weather records 1991-2010 show a 10% probability of 32°F. as of May 10th. 
Although cool weather may still occur in late April and May, the chance of a frost is decreasing. Cool season vegetables such as lettuce, carrots, cabbage and kale grow well in cool temperatures, but wait until the nights are consistently above 50°F. to plant warm season vegetables such as tomatoes, squash, peppers, eggplant and beans.  

Master Gardener seed trial picks favor hardy veggies

When selecting vegetable varieties, take a look at what Extension Master Gardeners have trialed and selected.  To learn about this year's winners and those from previous years in Minnesota, click on Master Gardener Seed Trial Results.

Author: Mary H. Meyer, Extension Horticulturist and Professor

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