Hardiness zone

Zone 3b

The coldest winter night here averages -35 to -30°F1. Frost dates vary more than that suggests.

ZIP codes: 230
Weather stations: 82
Last reviewed: 2026-11-02

Photo: Alexander Aubin / Pexels

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

Typical last frost: May 17most ZIPs May 11 – May 28
Typical first frost: Sep 24most ZIPs Sep 14 – Oct 1
Spread in spring: 17 daysbetween early and late ZIPs

Last spring frostmedian May 17Full range across the zone: May 4 to Jun 5Most of the zone (10th to 90th percentile): May 11 to May 28Zone median: May 17
First fall frostmedian Sep 24Full range across the zone: Sep 1 to Oct 4Most of the zone (10th to 90th percentile): Sep 14 to Oct 1Zone median: Sep 24

Frost-free season (median)

Figure 1. When frosts fall across zone 3b: the full range (pale), most ZIP codes (10th to 90th percentile, solid) and the median (marker). From 82 NOAA stations matched to 195 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 3b

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: Mar 16 to Apr 2Start indoors at the zone median: Mar 22 (Oregon State, central OR)Transplant outdoors across most of the zone: May 25 to Jun 11Transplant outdoors at the zone median: May 31 (Colorado State)
PeppersStart indoors across most of the zone: Mar 30 to Apr 16Start indoors at the zone median: Apr 5 (Oregon State, central OR)Transplant outdoors across most of the zone: May 25 to Jun 11Transplant outdoors at the zone median: May 31 (Colorado State)
CucumbersStart indoors across most of the zone: Apr 27 to May 14Start indoors at the zone median: May 3 (Oregon State, central OR)Transplant outdoors across most of the zone: May 18 to Jun 4Transplant outdoors at the zone median: May 24 (Oregon State, central OR)Sow outdoors across most of the zone: May 11 to May 28Sow outdoors at the zone median: May 17 (Colorado State)
ZucchiniStart indoors across most of the zone: May 4 to May 21Start indoors at the zone median: May 10 (Oregon State, central OR)Transplant outdoors across most of the zone: May 25 to Jun 11Transplant outdoors at the zone median: May 31 (Oregon State, central OR)Sow outdoors across most of the zone: May 11 to May 28Sow outdoors at the zone median: May 17 (Colorado State)
BeansStart indoors across most of the zone: Apr 20 to May 7Start indoors at the zone median: Apr 26 (Oregon State, central OR)Transplant outdoors across most of the zone: May 18 to Jun 4Transplant outdoors at the zone median: May 24 (Oregon State, central OR)Sow outdoors across most of the zone: May 11 to May 28Sow outdoors at the zone median: May 17 (Colorado State)
PeasStart indoors across most of the zone: Mar 16 to Apr 2Start indoors at the zone median: Mar 22 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 13 to Apr 30Transplant outdoors at the zone median: Apr 19 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 13 to May 14Sow outdoors at the zone median: Apr 19 to May 3 (Colorado State)
LettuceStart indoors across most of the zone: Mar 23 to Apr 9Start indoors at the zone median: Mar 29 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 27 to May 14Transplant outdoors at the zone median: May 3 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 13 to May 14Sow outdoors at the zone median: Apr 19 to May 3 (Colorado State)
CarrotsSow outdoors across most of the zone: Apr 27 to May 28Sow outdoors at the zone median: May 3 to May 17 (Colorado State)
OnionsStart indoors across most of the zone: Jan 20 to Feb 6Start indoors at the zone median: Jan 26 (Oregon State, central OR)Transplant outdoors across most of the zone: Mar 30 to Apr 16Transplant outdoors at the zone median: Apr 5 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 13 to May 14Sow outdoors at the zone median: Apr 19 to May 3 (Colorado State)
GarlicPlant for fall across most of the zone: Sep 21 to Oct 15Plant for fall at the zone median: Oct 1 to Oct 8 (Wisconsin)
PotatoesSow outdoors across most of the zone: Apr 27 to May 28Sow outdoors at the zone median: May 3 to May 17 (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 3b. 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 3b.
Crop	What	Zone median	Across most of the zone	Source
Tomatoes	Start indoors	Mar 22	Mar 16 – Apr 2	Oregon State, central OR3
Tomatoes	Transplant outdoors	May 31	May 25 – Jun 11	Colorado State4
Peppers	Start indoors	Apr 5	Mar 30 – Apr 16	Oregon State, central OR3
Peppers	Transplant outdoors	May 31	May 25 – Jun 11	Colorado State4
Cucumbers	Start indoors	May 3	Apr 27 – May 14	Oregon State, central OR3
	Transplant outdoors	May 24	May 18 – Jun 4	Oregon State, central OR3
	Sow outdoors	May 17	May 11 – May 28	Colorado State4
Zucchini	Start indoors	May 10	May 4 – May 21	Oregon State, central OR3
	Transplant outdoors	May 31	May 25 – Jun 11	Oregon State, central OR3
	Sow outdoors	May 17	May 11 – May 28	Colorado State4
Beans	Start indoors	Apr 26	Apr 20 – May 7	Oregon State, central OR3
	Transplant outdoors	May 24	May 18 – Jun 4	Oregon State, central OR3
	Sow outdoors	May 17	May 11 – May 28	Colorado State4
Peas	Start indoors	Mar 22	Mar 16 – Apr 2	Oregon State, central OR3
	Transplant outdoors	Apr 19	Apr 13 – Apr 30	Oregon State, central OR3
	Sow outdoors	Apr 19 – May 3	Apr 13 – May 14	Colorado State4
Lettuce	Start indoors	Mar 29	Mar 23 – Apr 9	Oregon State, central OR3
	Transplant outdoors	May 3	Apr 27 – May 14	Oregon State, central OR3
	Sow outdoors	Apr 19 – May 3	Apr 13 – May 14	Colorado State4
Carrots	Sow outdoors	May 3 – May 17	Apr 27 – May 28	Colorado State4
Onions	Start indoors	Jan 26	Jan 20 – Feb 6	Oregon State, central OR3
	Transplant outdoors	Apr 5	Mar 30 – Apr 16	Oregon State, central OR3
	Sow outdoors	Apr 19 – May 3	Apr 13 – May 14	Colorado State4
Garlic	Plant for fall	Oct 1 – Oct 8	Sep 21 – Oct 15	Wisconsin5
Potatoes	Sow outdoors	May 3 – May 17	Apr 27 – May 28	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.

Zone 3b

When to plant in zone 3b

Sources

Hi, I'm Pip!

First, I check for frost

Then I make your calendar

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