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Extension > Small Farms News > Soil Temperatures Needed for Germination

Wednesday, March 23, 2016

Soil Temperatures Needed for Germination

Source: Beth Berlin, University of Minnesota Extension

We had a glimpse of an early spring, but then temperatures dipped back down to close to normal. Many gardeners were ready to get a jump start on their gardens when it was so warm in early March. Although the frost is out early this year, soils need to reach a specific temperature in order for seeds to germinate. Here is a list of common vegetables and the minimum and optimal soil temperatures for seed germination:

Crop                              Min. Temp (F)     Optimal Temp. (F)
Bean                                    60                          60-85
Beet                                     40                          50-85
Cabbage, Carrot,
Cauliflower                            40                          45-85
Corn                                     50                          60-95
Cucumber                             60                          60-95
Eggplant                               60                          75-95
Lettuce                                 35                          40-80
Pea                                      40                          40-75
Radish                                  40                          45-90
Squash, Watermelon,
Muskmelon                            60                          70-95

Recognize that even if the minimum temperature is met, it may delay the number of days until the seedling appears. For example according to research done by J. F. Harrington, University of CA at Davis, a carrot planted at one-half inch that germinated in 41°F soil took 51 days for the seedling to appear while only 17 days when the soil temperature was 50°F. 

Other crops such as tomato and peppers in a typical year need to be started indoors or purchased as a transplant due to the number of days to maturity.  Read your seed packets to know specifics for that variety. For example, some varieties of tomato mature in 57 days where others require 70 days or even longer.

To determine your soil temperatures, purchase a soil thermometer from a local vendor or online supplier.  Success using other types of temperature gauges, such as a meat thermometer has shown some success as long as the thermometer reads lower temps. For more information about gardening visit www.extension.umn.edu/garden. 

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