FrostCal

When to Plant Onions in Idaho

In a typical Idaho location, start seeds indoors Feb 19 – Mar 5, then transplant outdoors Apr 2 – Apr 16. Across the state, the outdoor planting window starts as early as Mar 9 in Lewiston and as late as Apr 19 in Eagle. 2 cities in Idaho are essentially frost-free and can plant on a year-round schedule.

Method Start indoors, then transplant
Days to maturity 90–120 days

Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings.

Onions Planting Dates by City

CityStart indoorsTransplant
BoiseFeb 13 – Feb 27Mar 27 – Apr 10
MeridianFeb 13 – Feb 27Mar 27 – Apr 10
NampaFeb 18 – Mar 4Apr 1 – Apr 15
Idaho FallsFeb 28 – Mar 14Apr 11 – Apr 25
PocatelloFeb 21 – Mar 7Apr 4 – Apr 18
CaldwellFeb 12 – Feb 26Mar 26 – Apr 9
Coeur d'AleneFeb 11 – Feb 25Mar 25 – Apr 8
Twin FallsFeb 19 – Mar 5Apr 2 – Apr 16
LewistonJan 26 – Feb 9Mar 9 – Mar 23
Lewiston OrchardsJan 26 – Feb 9Mar 9 – Mar 23
Post FallsFeb 11 – Feb 25Mar 25 – Apr 8
RexburgMar 6 – Mar 20Apr 17 – May 1
MoscowFrost-free: year-round planting
EagleMar 8 – Mar 22Apr 19 – May 3
CondaFrost-free: year-round planting
KunaFeb 13 – Feb 27Mar 27 – Apr 10
AmmonFeb 28 – Mar 14Apr 11 – Apr 25
ChubbuckFeb 21 – Mar 7Apr 4 – Apr 18
HaydenFeb 11 – Feb 25Mar 25 – Apr 8
Mountain HomeFeb 21 – Mar 7Apr 4 – Apr 18
BlackfootFeb 24 – Mar 10Apr 7 – Apr 21
Garden CityFeb 13 – Feb 27Mar 27 – Apr 10
JeromeFeb 21 – Mar 7Apr 4 – Apr 18
BurleyFeb 26 – Mar 12Apr 9 – Apr 23

Showing the 24 most populous of 24 Idaho cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Idaho cities.

Frequently Asked Questions

When should I plant onions in Idaho?

In a typical Idaho location, start seeds indoors Feb 19 – Mar 5, then transplant outdoors Apr 2 – Apr 16. Across the state, the outdoor planting window starts as early as Mar 9 in Lewiston and as late as Apr 19 in Eagle. 2 cities in Idaho are essentially frost-free and can plant on a year-round schedule.

When is the last frost in Idaho?

The average last spring frost in Idaho ranges from April 6 in Lewiston to May 17 in Eagle, based on NOAA 1991–2020 climate normals.

How long do onions take to grow?

Onions typically take 90–120 days from planting to harvest. Start seeds indoors 8-10 weeks before last frost (or use sets/transplants); set out 2-4 weeks before last frost, very cold-tolerant as seedlings.

Other Crops in Idaho

When to plant onions in other states

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