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Regional Calendars, Climate & DataSoil Temperature Maps by Region
Soil temperature is a better planting signal than the calendar, and regional maps make it easy to see when soils are warming. They still need a check against your own field.
Key points
- Use soil temperature at seed depth, not the date, as your planting signal.
- Corn and soybeans are commonly planted once soil holds near 50 degrees F, but check your state guide for other crops.
- Regional maps are a starting point: depth, ground cover and timing of the reading all change the number.
- Check the forecast for cold rain after planting, and confirm insurance planting dates.
Why does soil temperature matter more than the date?
Seeds respond to the temperature around them, not to the day of the month. Nebraska CropWatch cites an average soil temperature of about 50 degrees F as the point where germination is expected to be reliable for corn and soybeans. Iowa State Extension makes the same point: a fixed date is not viable, and planting should start once soils have risen above 50 degrees F and are expected to keep rising.
Other crops have their own minimums, so check your state extension planting guide for the range for your area and crop.
What do regional soil temperature maps show?
Many state climate offices, universities and mesonets publish maps or tables of soil temperature from weather stations, often at a few inches of depth. They show how warming moves across a state in spring, which is useful for deciding when to start field work in each area.
Check which depth the map reports, whether it is a daily average or a morning reading, and what kind of ground cover the sensor sits under. Many stations measure under sod, which tends to stay cooler than tilled, bare ground.
Where and when should you measure on your own farm?
Place a thermometer or sensor at about seed depth. The Nebraska study cited above used an average of 1.75 inches, and Iowa State refers to soil at two inches for soybeans. Take readings at the same time each morning, since morning is usually the coolest point in the day, or use a logger that records hourly so you can see daily averages and lows.
Look for several consecutive days above your threshold, not a single warm afternoon.
A simple routine works well: probe at seed depth in the morning, write down the number and the field, and repeat for several days. After a week you have a trend you can trust far more than a single reading.
- Same depth every time
- Same time of day
- Several fields and exposures
- Write each reading down
What else changes soil warming?
Residue, moisture, slope and soil type all matter. Nebraska CropWatch notes that dryland wheat stubble warms faster than irrigated corn or soybean residue. Wet soil warms more slowly than dry soil. South-facing slopes warm earlier, while low, heavy ground lags.
Moisture and temperature work together: adequate moisture speeds water uptake by seed, but cold, wet soil is exactly where chilling injury becomes more likely.
How should you read the map against the forecast?
A map shows what has happened, not what is coming. A warm week can be followed by a cold snap, and seed that has already taken up water in cold soil can emerge slowly and unevenly. Penn State Extension describes the first day or two after planting as the window when imbibitional chilling is most likely.
Check the forecast for cold rain or a sharp cooldown in the days after planting, and be willing to wait.
What are the common mistakes?
Using air temperature as a stand-in for soil temperature. Reading a map station that sits under sod and applying it to bare ground. Ignoring crop insurance planting dates, which can limit how early you plant even when soil is warm. Check dates with your agent and the USDA Risk Management Agency.
A map gets you into the right week. Your own thermometer picks the day.
Also remember that the 50 degree figure belongs to corn and soybeans in the sources above. Other crops start at different temperatures, and some cool-season crops germinate well in much cooler soil, so look up the crop in your state extension guide.
How do you build your own soil temperature record?
Choose two or three representative fields and leave a thermometer or logger at seed depth each spring. Write down the reading, the time and what the ground cover was. If you tilled one field and left residue on another, record that as well, since it explains differences that otherwise look random.
Over a few seasons you will learn how much earlier your warm field reaches your threshold than your cold one. That gap is more useful than any regional map, because it tells you which field to plant first.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.