Frost Concerns After an Early Planting Season

By Liz Stahl, Extension Educator – Crops, Seth Naeve, Extension Soybean Agronomist, and Dave Nicolai, Extension Educator-Crops

Soybeans emerging in a cereal rye cover crop in Martin County
May 5, 2026. Photo credit: Rochelle Krusemark.

With good field conditions, many acres of soybean and corn were planted across southern MN by mid to late April. Corn and soybean in some of these fields were just starting to or have emerged. The frost warnings issued yesterday (May 5) were not a welcome development. According to the NDAWN and MN Department of Agriculture’s Agriculture Weather Network (Figure 1), although some areas dodged freezing temperatures, minimum temperatures down to 24°F were recorded in parts SW, SC, SE, and NW Minnesota. What does this mean for crops that were planted early and are emerging or have emerged?  

When can I expect crop emergence?

Check on crop emergence. It takes about 90 to 120 cumulative growing degree units (GDUs) for corn emergence and about 130 to cumulative GDUs for soybean emergence (base of 50 degrees F). To calculate GDUs, often referred to as growing degree-days (GDDs), take the average daily temperature ((max temperature + min temperature)/2)) and subtract 50. In the calculation, use 86 for temperatures above 86°F, and use 50 for temperatures below 50°F.  

Fig 1. Minimum temperatures the morning of May 6, 2026. 
Source: NDAWN & the MN Department of Agriculture. 

Assessing frost injury and making replant decisions

Soybean: Temperatures usually need to be at or below 28 to 30°F for several hours to kill soybean tissue. Even if air temperatures hit 28°F, emerged soybeans may still not freeze. Wait three to five days before assessing stands as it takes some time to tell if plants will recover from frost injury.

The article Spring frost damage on soybean discusses how to assess frost injury. If injury is detected, the article Soybean damage and replanting addresses considerations when making replant decisions. Soybeans do have tremendous potential to compensate for losses in stand, but things such as weed control, need to be taken into consideration. Higher fuel costs should also be added to the equation this year when deciding whether or not to replant or supplement a reduced stand.

Corn: The article Spring freeze injury in corn addresses how to assess frost injury in corn and considerations when making replant decisions. A big plus for corn this early in the season is that the corn plant’s growing point is below the ground and will be there until corn reaches the V5 to V6 stage. This means that unless we have temperatures that are low enough to freeze the upper part of the soil where the growing point is, seedlings should survive.

Join us for the 2026 season of Strategic Farming Field Notes:

Join us for the 2026 season of Strategic Farming: Field Notes to discuss cropping issues as they arise throughout the season. You can join live over Zoom every Wednesday morning from 8:00 to 8:30 from May 13 through August 12, or listen to the podcast recording of the program as it fits into your schedule. Register now for the for the series (you only need to register one time for the whole series) at z.umn.edu/strategicfarming. There is no cost to join, thanks to our sponsors, the MN Soybean Research and Promotion Council and the MN Corn Research and Promotion Council.