Frost Risk Calculator
Judge how dangerous a forecast low temperature is for your crop. The tool combines critical temperatures by crop stage, crop sensitivity and topographic cold-air drainage to give a risk level and protection advice.
Results
How to Use This Calculator
Take the forecast overnight low temperature, pick the crop's current growth stage, the crop type, and the field's topography. Click Calculate. Depressions hold cold air (worst case); slopes drain cold air away (best case).
About This Tool
About
Applicability: Applicable to major field crops (corn, soybeans, wheat) in North America and Europe, adaptable worldwide.
How the Calculation Works
Risk is computed by comparing local minimum temperature (forecast + topography adjustment) to the crop-stage critical temperature, further lowered for sensitive fruit/grape crops. Roughly: > -2°C is safe; -2 to -4°C is moderate; below -4°C is severe. Protection: overhead irrigation releases latent heat as water freezes (keep it running until thaw), wind machines mix warm air down, and covers/smudge pots protect small areas. Common mistakes: trusting airport forecasts for low-lying fields, waiting until morning to act, and assuming one frost kills a fully mature crop.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- NOAA National Weather Service — Frost and Freeze
- Penn State Extension — Frost Protection
- USDA — Crop Weather and Freeze Advisories
Frequently Asked Questions
What temperature kills corn blossoms?
Corn pollen and silks are highly sensitive around tasseling/silking: temperatures of -1 to -2°C for even a short time can kill pollen and reduce fertilization, causing poor kernel set.
Does overhead irrigation really protect against frost?
Yes, because water releases latent heat as it freezes onto the plant, holding tissue near 0°C. Keep water running continuously from before frost through thaw — turning it off mid-freeze makes things worse. It fails during severe freezes with high wind.
Why are low hollows colder than the forecast?
Cold air is denser and drains downhill like water, pooling in depressions at night. A valley can run 2-4°C colder than a nearby hilltop or the town weather station. Always apply a depression adjustment for low fields.
Which crop stages are most frost-sensitive?
Flowering and early fruit set are the most sensitive (near -1 to -2°C), because reproductive organs are tender. Seedlings and grain fill are next; dormant mature plants and winter wheat are the hardiest.
When should I start frost protection?
Start before the temperature reaches the critical point, typically when the forecast low is within 1-2°C of critical and skies are clear/calm (radiation frost conditions). You cannot warm a fully frozen crop. Run systems continuously until temperatures rise above freezing.
