Frost means that an object reached a temperature of 32°F or lower. However, the local air temperature measured at five feet above ground is likely several degrees higher. Similarly, not every air temperature at or below 32°F means frost will form. Despite the fact that frost is not fully predicted by air temperature, the average date of the first or last air temperature of 32° has traditionally been called the frost date.

Average dates

On a daily basis, if the temperature drops below 40°F by 10pm, be prepared for frost.

First fall frost
Last spring frost Oct 21 ± 10 days
Apr 15 ± 12 days

Growing season

The growing season is the number of consecutive days above an air temperature of 32 degees. The growing season for Orange County is 190 ±14 days.

Resources

• Plantmaps lets you see how the dates vary with geography. Use Zoom to Zipcode for details.
  Fall Spring
• AgroClimate shows freeze likelihood maps. You input the date range.
• The National Weather Service shows maps for median/earliest/latest dates of 32 degree and 28 degree spring and fall freezes for the most recent 30-year period of record. Because temperature is measured at five feet above the ground, plant surfaces can be colder than the air temperature suggests.