A hard freeze is when most annual plants, and the tops of some perennial flowers in an area, are frozen. A killing frost, which kills annuals and often occurs earlier than a hard freeze, isn't generally as severe. Previous light freezes may damage/kill the tenderest annuals and perhaps parts of other hardier annuals, but often not all of the plant. Annuals can include flowers, vegetables, and herbs.
The classification of freeze temperatures is usually based on their effect on plants, with the following commonly accepted categories:
Light freeze:
- 29 degrees F to 32 degrees F
- Tender plants killed, with little destructive effect on other vegetation
Moderate freeze:
- 25 degrees F to 28 degrees F
- Widely destructive effect on most vegetation, with heavy damage to fruit blossoms and tender and semihardy plants
Severe freeze:
- 24 degrees F and colder
