Frost Date Lookup

Frost dates are based on historical climate data from NOAA weather stations across the United States. The dates represent averages calculated from decades of temperature records, typically using the standard threshold of 32°F (0°C).

Key Terms

• Last Spring Frost — The average date of the last occurrence of 32°F or below in spring. After this date, the risk of frost drops significantly.
• First Fall Frost — The average date of the first occurrence of 32°F or below in fall. This marks the typical end of the outdoor growing season.
• Growing Season — The number of frost-free days between the last spring frost and first fall frost.

Probability Ranges

Because weather varies year to year, frost dates are expressed as probabilities. A “50% probability” means the last frost occurs before that date in half of all years. For safer planting, use the 10% date (90% of years will have their last frost before this date). For risk-tolerant gardeners, the 90% date offers an earlier start but with higher frost risk.

Limitations

• Frost dates are averages and can vary significantly year to year
• Microclimates (urban heat islands, elevation, proximity to water) affect local frost dates
• Climate change may be shifting historical averages—recent years may trend warmer
• Data is based on US weather stations; locations between stations are interpolated

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