Zone 6a

The coldest winter night here averages -10 to -5°F1. Frost dates vary more than that suggests.

ZIP codes: 5,187
Weather stations: 924
Last reviewed: 2026-11-02

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

Typical last frost: Apr 28most ZIPs Apr 16 – May 10
Typical first frost: Oct 17most ZIPs Oct 5 – Oct 24
Spread in spring: 24 daysbetween early and late ZIPs

Last spring frostmedian Apr 28Full range across the zone: Apr 4 to Jun 21Most of the zone (10th to 90th percentile): Apr 16 to May 10Zone median: Apr 28
First fall frostmedian Oct 17Full range across the zone: Sep 6 to Nov 12Most of the zone (10th to 90th percentile): Oct 5 to Oct 24Zone median: Oct 17

Frost-free season (median)

Figure 1. When frosts fall across zone 6a: the full range (pale), most ZIP codes (10th to 90th percentile, solid) and the median (marker). From 924 NOAA stations matched to 4,375 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 6a

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 20 to Mar 15Start indoors at the zone median: Mar 3 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 30 to May 24Transplant outdoors at the zone median: May 12 (Colorado State)
PeppersStart indoors across most of the zone: Mar 5 to Mar 29Start indoors at the zone median: Mar 17 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 30 to May 24Transplant outdoors at the zone median: May 12 (Colorado State)
CucumbersStart indoors across most of the zone: Apr 2 to Apr 26Start indoors at the zone median: Apr 14 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 23 to May 17Transplant outdoors at the zone median: May 5 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 16 to May 10Sow outdoors at the zone median: Apr 28 (Colorado State)
ZucchiniStart indoors across most of the zone: Apr 9 to May 3Start indoors at the zone median: Apr 21 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 30 to May 24Transplant outdoors at the zone median: May 12 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 16 to May 10Sow outdoors at the zone median: Apr 28 (Colorado State)
BeansStart indoors across most of the zone: Mar 26 to Apr 19Start indoors at the zone median: Apr 7 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 23 to May 17Transplant outdoors at the zone median: May 5 (Oregon State, central OR)Sow outdoors across most of the zone: Apr 16 to May 10Sow outdoors at the zone median: Apr 28 (Colorado State)
PeasStart indoors across most of the zone: Feb 20 to Mar 15Start indoors at the zone median: Mar 3 (Oregon State, central OR)Transplant outdoors across most of the zone: Mar 19 to Apr 12Transplant outdoors at the zone median: Mar 31 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 19 to Apr 26Sow outdoors at the zone median: Mar 31 to Apr 14 (Colorado State)
LettuceStart indoors across most of the zone: Feb 27 to Mar 22Start indoors at the zone median: Mar 10 (Oregon State, central OR)Transplant outdoors across most of the zone: Apr 2 to Apr 26Transplant outdoors at the zone median: Apr 14 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 19 to Apr 26Sow outdoors at the zone median: Mar 31 to Apr 14 (Colorado State)
CarrotsSow outdoors across most of the zone: Apr 2 to May 10Sow outdoors at the zone median: Apr 14 to Apr 28 (Colorado State)
OnionsStart indoors across most of the zone: Dec 26 to Jan 19Start indoors at the zone median: Jan 7 (Oregon State, central OR)Transplant outdoors across most of the zone: Mar 5 to Mar 29Transplant outdoors at the zone median: Mar 17 (Oregon State, central OR)Sow outdoors across most of the zone: Mar 19 to Apr 26Sow outdoors at the zone median: Mar 31 to Apr 14 (Colorado State)
GarlicPlant for fall across most of the zone: Oct 12 to Nov 7Plant for fall at the zone median: Oct 24 to Oct 31 (Wisconsin)
PotatoesSow outdoors across most of the zone: Apr 2 to May 10Sow outdoors at the zone median: Apr 14 to Apr 28 (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 6a. 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 6a.
Crop	What	Zone median	Across most of the zone	Source
Tomatoes	Start indoors	Mar 3	Feb 20 – Mar 15	Oregon State, central OR3
Tomatoes	Transplant outdoors	May 12	Apr 30 – May 24	Colorado State4
Peppers	Start indoors	Mar 17	Mar 5 – Mar 29	Oregon State, central OR3
Peppers	Transplant outdoors	May 12	Apr 30 – May 24	Colorado State4
Cucumbers	Start indoors	Apr 14	Apr 2 – Apr 26	Oregon State, central OR3
	Transplant outdoors	May 5	Apr 23 – May 17	Oregon State, central OR3
	Sow outdoors	Apr 28	Apr 16 – May 10	Colorado State4
Zucchini	Start indoors	Apr 21	Apr 9 – May 3	Oregon State, central OR3
	Transplant outdoors	May 12	Apr 30 – May 24	Oregon State, central OR3
	Sow outdoors	Apr 28	Apr 16 – May 10	Colorado State4
Beans	Start indoors	Apr 7	Mar 26 – Apr 19	Oregon State, central OR3
	Transplant outdoors	May 5	Apr 23 – May 17	Oregon State, central OR3
	Sow outdoors	Apr 28	Apr 16 – May 10	Colorado State4
Peas	Start indoors	Mar 3	Feb 20 – Mar 15	Oregon State, central OR3
	Transplant outdoors	Mar 31	Mar 19 – Apr 12	Oregon State, central OR3
	Sow outdoors	Mar 31 – Apr 14	Mar 19 – Apr 26	Colorado State4
Lettuce	Start indoors	Mar 10	Feb 27 – Mar 22	Oregon State, central OR3
	Transplant outdoors	Apr 14	Apr 2 – Apr 26	Oregon State, central OR3
	Sow outdoors	Mar 31 – Apr 14	Mar 19 – Apr 26	Colorado State4
Carrots	Sow outdoors	Apr 14 – Apr 28	Apr 2 – May 10	Colorado State4
Onions	Start indoors	Jan 7	Dec 26 – Jan 19	Oregon State, central OR3
	Transplant outdoors	Mar 17	Mar 5 – Mar 29	Oregon State, central OR3
	Sow outdoors	Mar 31 – Apr 14	Mar 19 – Apr 26	Colorado State4
Garlic	Plant for fall	Oct 24 – Oct 31	Oct 12 – Nov 7	Wisconsin5
Potatoes	Sow outdoors	Apr 14 – Apr 28	Apr 2 – May 10	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.