Frost & Plant Hardiness Temperature Guide

Know how cold your garden gets. USDA hardiness zones are based on average extreme winter lows, and frost severity determines which plants survive a cold night.

USDA plant hardiness zones

Zone	Average extreme minimum
1	-60 to -50 °F (-51 to -46 °C)
2	-50 to -40 °F (-46 to -40 °C)
3	-40 to -30 °F (-40 to -34 °C)
4	-30 to -20 °F (-34 to -29 °C)
5	-20 to -10 °F (-29 to -23 °C)
6	-10 to 0 °F (-23 to -18 °C)
7	0 to 10 °F (-18 to -12 °C)
8	10 to 20 °F (-12 to -7 °C)
9	20 to 30 °F (-7 to -1 °C)
10	30 to 40 °F (-1 to 4 °C)
11	40 to 50 °F (4 to 10 °C)
12	50 to 60 °F (10 to 16 °C)
13	60 to 70 °F (16 to 21 °C)

Frost categories

Type	Temperature	Effect
Light frost	29–32 °F (-2–0 °C)	Kills tender plants (basil, tomatoes, peppers)
Moderate freeze	25–28 °F (-4–-2 °C)	Damages most vegetation and blossoms
Severe / hard freeze	24 °F (-4 °C) and below	Heavy damage to most plants

Notes

Frost can form when air temperatures are slightly above freezing, especially on clear, calm nights when plants radiate heat. Cover tender plants with frost cloth before sunset, water the soil (moist soil holds heat) and bring containers indoors. Each zone is split into “a” and “b” halves 5 °F apart. Zones describe winter cold only — summer heat matters too.

Frequently asked questions

What temperature is frost?

Frost can form when air near the ground reaches 32 °F (0 °C) or slightly above on clear nights.

What temperature kills tomato plants?

Freezing temperatures (32 °F) kill tomatoes; growth suffers below about 50 °F.