Light Frost vs Hard Freeze: What 36°F, 32°F, and 28°F Mean for Plants
The difference between a light frost, a freeze, and a hard freeze, which plants each one damages, and how to read the three frost dates on your ZIP code page.
Last updated 2026-10-01
Light frost (36°F)
On clear, still nights, leaves and grass lose heat faster than the surrounding air and can drop below freezing while a thermometer at eye level reads the mid-30s. Ice crystals form on the plant surface. Basil, tomatoes, peppers, cucumbers, squash, and many annual flowers can be scarred or killed by a light frost.
Freeze (32°F)
When the air temperature reaches 32°F, water inside tender plant tissue freezes and ruptures cells. Warm-season vegetables are usually damaged or killed; leaves turn dark and limp the next morning. Cool-season crops such as lettuce, peas, and broccoli usually come through a brief 32°F night.
Hard freeze (28°F)
At 28°F and below, often called a hard or killing freeze, most annual plants die and the effective end of the warm-season garden arrives. Pumpkins, winter squash, potatoes, and sweet potatoes can be injured, so harvest them first. Hardy greens such as kale, collards, and cabbage tolerate it, and their flavor often improves after cold weather.
Using the three dates
Each ZIP code page lists spring and fall dates for all three temperatures. Use the 36°F dates for the most tender plants, the 32°F dates for general planning, and the 28°F fall dates for the final harvest of hardier crops.