Zone 5b

The coldest winter night here averages -15 to -10°F1. Frost dates vary more than that suggests.

ZIP codes: 2,880
Weather stations: 687
Last reviewed: 2026-11-02

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

Typical last frost: May 1most ZIPs Apr 21 – May 17
Typical first frost: Oct 11most ZIPs Oct 1 – Oct 19
Spread in spring: 26 daysbetween early and late ZIPs

Last spring frostmedian May 1Full range across the zone: Apr 8 to Jun 21Most of the zone (10th to 90th percentile): Apr 21 to May 17Zone median: May 1
First fall frostmedian Oct 11Full range across the zone: Sep 2 to Oct 29Most of the zone (10th to 90th percentile): Oct 1 to Oct 19Zone median: Oct 11

Frost-free season (median)

Figure 1. When frosts fall across zone 5b: the full range (pale), most ZIP codes (10th to 90th percentile, solid) and the median (marker). From 687 NOAA stations matched to 2,445 ZIP codes.

Zone and frost date are different things. The zone comes from the coldest winter night; frost dates come from spring and fall temperatures at weather stations2. Your own dates can sit anywhere in the range above, so the calendar for your ZIP is the better guide.

When to plant in zone 5b

Each crop uses its primary extension source, applied to this zone's frost spread. Rules written for another state are labelled with their source.

TomatoesStart indoors across most of the zone: Feb 25 to Mar 22Start indoors at the zone median: Mar 6 (Oregon State, central OR)Transplant outdoors across most of the zone: May 5 to May 31Transplant outdoors at the zone median: May 15 (Colorado State)
PeppersStart indoors across most of the zone: Mar 10 to Apr 5Start indoors at the zone median: Mar 20 (Oregon State, central OR)Transplant outdoors across most of the zone: May 5 to May 31Transplant outdoors at the zone median: May 15 (Colorado State)
CucumbersStart indoors across most of the zone: Apr 7 to May 3Start indoors at the zone median: Apr 17 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 28 to May 24Transplant outdoors at the zone median: May 8 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 21 to May 17Sow outdoors at the zone median: May 1 (Colorado State)
ZucchiniStart indoors across most of the zone: Apr 14 to May 10Start indoors at the zone median: Apr 24 (Oregon State, central OR)Transplant outdoors across most of the zone: May 5 to May 31Transplant outdoors at the zone median: May 15 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 21 to May 17Sow outdoors at the zone median: May 1 (Colorado State)
BeansStart indoors across most of the zone: Mar 31 to Apr 26Start indoors at the zone median: Apr 10 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 28 to May 24Transplant outdoors at the zone median: May 8 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 21 to May 17Sow outdoors at the zone median: May 1 (Colorado State)
PeasStart indoors across most of the zone: Feb 25 to Mar 22Start indoors at the zone median: Mar 6 (Oregon State, central OR)Transplant outdoors across most of the zone: Mar 24 to Apr 19Transplant outdoors at the zone median: Apr 3 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 24 to May 3Sow outdoors at the zone median: Apr 3 to Apr 17 (Colorado State)
LettuceStart indoors across most of the zone: Mar 3 to Mar 29Start indoors at the zone median: Mar 13 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 7 to May 3Transplant outdoors at the zone median: Apr 17 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 24 to May 3Sow outdoors at the zone median: Apr 3 to Apr 17 (Colorado State)
CarrotsSow outdoors across most of the zone: Apr 7 to May 17Sow outdoors at the zone median: Apr 17 to May 1 (Colorado State)
OnionsStart indoors across most of the zone: Dec 31 to Jan 26Start indoors at the zone median: Jan 10 (Oregon State, central OR)Transplant outdoors across most of the zone: Mar 10 to Apr 5Transplant outdoors at the zone median: Mar 20 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 24 to May 3Sow outdoors at the zone median: Apr 3 to Apr 17 (Colorado State)
GarlicPlant for fall across most of the zone: Oct 8 to Nov 2Plant for fall at the zone median: Oct 18 to Oct 25 (Wisconsin)
PotatoesSow outdoors across most of the zone: Apr 7 to May 17Sow outdoors at the zone median: Apr 17 to May 1 (Colorado State)
BasilNo sourced window

Start indoors
Plant outdoors
Range across the zone
Frost-free season (median)
Spring frost risk (90% to 10%)
Fall frost risk (10% to 90%)

Figure 2. Planting windows across zone 5b. Solid and dashed bars: the window at the zone's median frost dates. Pale bars: where the same window falls across most of the zone's ZIP codes.

Table 1. Planting windows in zone 5b.
Crop	What	Zone median	Across most of the zone	Source
Tomatoes	Start indoors	Mar 6	Feb 25 – Mar 22	Oregon State, central OR3
Tomatoes	Transplant outdoors	May 15	May 5 – May 31	Colorado State4
Peppers	Start indoors	Mar 20	Mar 10 – Apr 5	Oregon State, central OR3
Peppers	Transplant outdoors	May 15	May 5 – May 31	Colorado State4
Cucumbers	Start indoors	Apr 17	Apr 7 – May 3	Oregon State, central OR3
	Transplant outdoors	May 8	Apr 28 – May 24	Oregon State, central OR3
	Sow outdoors	May 1	Apr 21 – May 17	Colorado State4
Zucchini	Start indoors	Apr 24	Apr 14 – May 10	Oregon State, central OR3
	Transplant outdoors	May 15	May 5 – May 31	Oregon State, central OR3
	Sow outdoors	May 1	Apr 21 – May 17	Colorado State4
Beans	Start indoors	Apr 10	Mar 31 – Apr 26	Oregon State, central OR3
	Transplant outdoors	May 8	Apr 28 – May 24	Oregon State, central OR3
	Sow outdoors	May 1	Apr 21 – May 17	Colorado State4
Peas	Start indoors	Mar 6	Feb 25 – Mar 22	Oregon State, central OR3
	Transplant outdoors	Apr 3	Mar 24 – Apr 19	Oregon State, central OR3
	Sow outdoors	Apr 3 – Apr 17	Mar 24 – May 3	Colorado State4
Lettuce	Start indoors	Mar 13	Mar 3 – Mar 29	Oregon State, central OR3
	Transplant outdoors	Apr 17	Apr 7 – May 3	Oregon State, central OR3
	Sow outdoors	Apr 3 – Apr 17	Mar 24 – May 3	Colorado State4
Carrots	Sow outdoors	Apr 17 – May 1	Apr 7 – May 17	Colorado State4
Onions	Start indoors	Jan 10	Dec 31 – Jan 26	Oregon State, central OR3
	Transplant outdoors	Mar 20	Mar 10 – Apr 5	Oregon State, central OR3
	Sow outdoors	Apr 3 – Apr 17	Mar 24 – May 3	Colorado State4
Garlic	Plant for fall	Oct 18 – Oct 25	Oct 8 – Nov 2	Wisconsin5
Potatoes	Sow outdoors	Apr 17 – May 1	Apr 7 – May 17	Colorado State4
Basil	No frost-relative rule is published; sources give conditions instead (see the crop page).

Sources

PRISM Group, Oregon State University, 2023 USDA Plant Hardiness Zone Map ZIP code data (PHZM 2023), 2023-11-15. Retrieved 2026-11-02.
NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
Oregon State University Extension Service, When to start seeds indoors in central Oregon, reviewed 2024. Retrieved 2026-11-02.
Colorado State University Extension, Vegetable Planting Guide (CMG GardenNotes #720), reviewed September 2024. Retrieved 2026-11-02.
University of Wisconsin–Madison Division of Extension, Wisconsin Horticulture, Garlic, Allium sativum, Rev: 10/2023. Retrieved 2026-11-02.