Cardinal Temperature Emergence & Is Your Soil Warm Enough to Sow?
Times maize
Germination tools assume a fixed days-to-emerge; real soils don't. Enter your crop and the measured soil temperature to get the predicted days to emergence, expected emergence percent and a below-base do-not-sow flag, flexed by each species' base, optimum and ceiling temperatures.
Crop & soil temperature
Next: emergence will take ~7.5 days; if you can wait for soil to reach 26°C+ you will cut that time and lift the stand to ~95%.
Days = thermal time ÷ effective GDD per day; effective GDD is 0 below base, rises to a peak at optimum, then declines to the ceiling.
Cardinal-temperature emergence — key facts
- GDD per day
- effective °C above base, capped at optimum
- Days to emerge
- thermal time ÷ GDD per day
- Below base
- no accumulation → do not sow
- Above ceiling
- no emergence → too hot
- Prompt window
- ~80% to optimum, up to optimum
- Crops covered
- 16 warm- and cool-season species
- Measured at
- soil temp, ~5 cm seeding depth
- Privacy
- Runs in your browser; nothing uploaded
Cardinal temperatures & thermal time by crop
Base, optimum and ceiling temperatures (°C) and the thermal time to emergence (°C-days above base) used by the calculator. Representative planning values from published germination thermal-time studies and agronomy handbooks.
| Crop | Season | Base °C | Optimum °C | Ceiling °C | °C-days to emerge |
|---|---|---|---|---|---|
| Maize (corn) | warm | 10 | 30 | 40 | 60 |
| Sorghum | warm | 10 | 32 | 42 | 55 |
| Cotton | warm | 14 | 32 | 40 | 50 |
| Soybean | warm | 8 | 30 | 40 | 70 |
| Sunflower | warm | 6 | 28 | 38 | 65 |
| Rice | warm | 12 | 30 | 40 | 60 |
| Wheat | cool | 2 | 22 | 35 | 90 |
| Barley | cool | 2 | 20 | 32 | 85 |
| Canola (rapeseed) | cool | 3 | 22 | 32 | 70 |
| Field pea | cool | 4 | 20 | 30 | 95 |
| Lentil | cool | 3 | 22 | 32 | 90 |
| Chickpea | cool | 5 | 25 | 35 | 85 |
| Tomato | warm | 10 | 29 | 38 | 75 |
| Lettuce | cool | 2 | 22 | 28 | 55 |
| Carrot | cool | 4 | 24 | 32 | 110 |
| Onion | cool | 3 | 24 | 32 | 120 |
Temperature, not the calendar, drives emergence
A seed germinates by accumulating heat, not by counting days. Each crop must bank a fixed amount of thermal time — growing degree-days above its base temperature — before the shoot reaches the surface. How fast it banks that heat depends entirely on soil temperature: nothing accumulates at or below the base, accumulation peaks at the optimum, and it falls away again toward the ceiling. That is why the same hybrid emerges in under a week in warm soil and crawls for three weeks in cold soil, and why sowing into below-base ground simply rots seed.
This tool turns a measured soil temperature into the days to emergence, expected emergence percent, a do-not-sow flag and the prompt sowing window for sixteen crops. Use it to decide whether to sow today or wait, to compare warm- and cool-season options for a cold seedbed, and to set realistic stand expectations. Pair it with the GDD-to-Maturity, Variety Trait Selector and Field Establishment tools for a full crop-planning workflow.
How to use it — five steps
- 1Select your crop — the tool loads its base, optimum and ceiling temperatures.
- 2Measure soil temperature at seeding depth in the morning, over several days.
- 3Read the predicted days to emergence and the expected-emergence percent.
- 4Check the verdict — a below-base reading flags do-not-sow.
- 5Sow inside the prompt window for the fastest, most uniform stand, or wait if it is too cold.
Frequently Asked Questions
How does the calculator predict days to emergence?+
Emergence needs a fixed amount of thermal time — growing degree-days above the crop's base temperature. The tool finds the effective degree-days your soil delivers per day (zero at or below the base temperature, rising to a peak at the optimum, then falling toward the ceiling), then divides the crop's thermal-time requirement by that daily rate. Maize, for example, needs about 60 degree-days; at a steady 20°C soil it earns 10 a day (20 − 10°C base), so it emerges in about six days.
What are cardinal temperatures?+
Every species has three cardinal temperatures: a base (minimum) below which germination effectively stops, an optimum where it is fastest, and a maximum (ceiling) above which it stops again. Maize is roughly base 10°C, optimum 30°C, ceiling 40°C; cool-season wheat is about base 2°C, optimum 22°C, ceiling 35°C. The tool stores these for each crop and uses them to flex the days-to-emerge with your measured soil temperature.
When is it too cold to sow?+
When your soil temperature is at or below the crop's base temperature, no thermal time accumulates, so emergence is effectively indefinite — the tool shows a do-not-sow flag. Sowing into below-base soil risks rot, chilling injury and very patchy stands. Wait until the soil climbs into the crop's prompt window before planting.
What soil temperature should I sow at?+
Aim for the prompt window the tool reports — the band, from about 80% of the way to optimum up to the optimum itself, where emergence is fastest and most uniform. For maize that is roughly 26–30°C, for wheat the upper teens to low twenties. Sowing inside this window typically gives near-95% expected emergence.
How should I measure soil temperature?+
Measure at seeding depth — about 5 cm for most field crops — using a soil thermometer, ideally in the morning when the soil is at its daily low, for several days running. Bare, dark, well-drained soil warms faster than wet, residue-covered ground. Use the steady reading you expect over the days after sowing, not a single warm afternoon.
Why does emergence slow above the optimum too?+
Above the optimum, the effective degree-day rate declines toward the ceiling rather than continuing to rise, because heat begins to stress the germinating seed. So very hot seedbeds can be as poor as cold ones: the tool models this decline, and above the ceiling it flags the soil as too hot with no emergence.
What is the expected-emergence percent?+
It is a guide to how complete and even your stand should be at the entered temperature. It plateaus near 95% across the favourable band, ramps down as you approach the base temperature and tapers off toward the ceiling. A low percent warns that even if seedlings do emerge, the stand will be thin and uneven.
Does the prediction depend on moisture or seed depth?+
The model is temperature-driven and assumes adequate moisture and a normal sowing depth — the usual limiting factor for emergence once moisture is sufficient. Dry soil, crusting, deep sowing or poor seed-to-soil contact will all slow emergence beyond what temperature alone predicts, so treat the result as the best case for your soil temperature.
Should I sow now or wait for warmer soil?+
If the soil is below the base temperature, wait — sowing gains nothing and risks the seed. If it is in or near the prompt window, sow now. If it is between base and prompt, you can sow but expect slower, patchier emergence; the decision then weighs the calendar (frost, season length) against waiting a few days for soil that emerges the crop faster and more evenly.
Are these cardinal temperatures exact for my cultivar?+
They are representative planning values for each species, compiled from published germination thermal-time studies and agronomy handbooks, not a single named cultivar. Cultivars vary, so use the result to compare scenarios and time your sowing, and refine with local trial data or your seed company's specific figures where you have them.
Which crops does the tool cover?+
Sixteen — warm-season maize, sorghum, cotton, soybean, sunflower, rice and tomato, and cool-season wheat, barley, canola, field pea, lentil, chickpea, lettuce, carrot and onion. Each carries its own base, optimum and ceiling temperatures and thermal-time-to-emergence in the reference table below.