Hardiness zones

Each zone's winter low, and when frosts actually fall across its ZIP codes.

Your zone tells you how cold winter gets. It does not tell you when to plant.

Table 1. Zones from the 2023 PRISM ZIP data; frost dates from NOAA 1991-2020 normals, as the median of each ZIP's station.
Zone	Winter low (°F)	Typical last frost	Typical first frost	ZIP codes
1a	-60 to -55	May 25 (May 25 – May 25)	Aug 26 (Aug 26 – Aug 26)	5
1b	-55 to -50	May 18 (May 18 – May 29)	Aug 28 (Aug 28 – Sep 8)	11
2a	-50 to -45	May 20 (May 13 – May 25)	Sep 4 (Sep 1 – Sep 8)	27
2b	-45 to -40	May 13 (May 13 – May 18)	Sep 6 (Sep 6 – Sep 17)	17
3a	-40 to -35	May 29 (May 23 – Jun 10)	Sep 13 (Sep 11 – Sep 21)	23
3b	-35 to -30	May 17 (May 11 – May 28)	Sep 24 (Sep 14 – Oct 1)	230
4a	-30 to -25	May 12 (May 5 – May 24)	Sep 28 (Sep 20 – Oct 4)	814
4b	-25 to -20	May 8 (May 1 – May 25)	Oct 1 (Sep 22 – Oct 8)	1,284
5a	-20 to -15	May 3 (Apr 26 – May 20)	Oct 5 (Sep 26 – Oct 13)	2,426
5b	-15 to -10	May 1 (Apr 21 – May 17)	Oct 11 (Oct 1 – Oct 19)	2,880
6a	-10 to -5	Apr 28 (Apr 16 – May 10)	Oct 17 (Oct 5 – Oct 24)	5,187
6b	-5 to 0	Apr 22 (Apr 10 – May 3)	Oct 22 (Oct 10 – Oct 29)	5,271
7a	0 to 5	Apr 16 (Apr 4 – Apr 28)	Oct 25 (Oct 16 – Nov 2)	4,877
7b	5 to 10	Apr 5 (Mar 30 – Apr 17)	Nov 1 (Oct 24 – Nov 14)	3,855
8a	10 to 15	Mar 29 (Mar 20 – Apr 7)	Nov 6 (Oct 31 – Nov 14)	3,413
8b	15 to 20	Mar 17 (Mar 6 – Apr 1)	Nov 13 (Nov 4 – Nov 23)	3,379
9a	20 to 25	Mar 2 (Feb 16 – Mar 18)	Nov 26 (Nov 16 – Dec 9)	2,199
9b	25 to 30	Feb 2 (Jan 12 – Feb 26)	Dec 14 (Nov 30 – Jan 5)	2,085
10a	30 to 35	Jan 17 (Jan 2 – Jan 30)	Jan 3 (Dec 19 – Jan 13)	1,234
10b	35 to 40	Jan 16 (Jan 4 – Jan 24)	Jan 13 (Dec 25 – Jan 17)	752
11a	40 to 45	Jan 18 (Jan 16 – Jan 22)	Jan 13 (Jan 13 – Jan 17)	205
11b	45 to 50	Frost rare	Frost rare	16
12a	50 to 55	Frost rare	Frost rare	30
12b	55 to 60	Jan 26 (Jan 26 – Jan 26)	Jan 24 (Jan 24 – Jan 24)	137
13a	60 to 65	Frost rare	Frost rare	102
13b	65 to 70	Frost rare	Frost rare	26