When to plant onions in Idaho

Onions
Plant out in Boise City
Mar 13–Apr 3

Across Idaho the window opens between February 23 and March 31. Find your city below; the dates follow each town's own average last frost.

Start indoors, Boise City
Jan 30–Feb 27
Plant out, Boise City
Mar 13–Apr 3
Last frost, Boise City
Apr 24

Start seeds indoors 8–12 weeks before the last frost; plant out 3–6 weeks before the last frost. Northern gardens need long-day varieties and southern gardens need short-day ones. A wrong pick gives small bulbs.

Onions planting dates by city

Start indoorsPlant outSow outdoorsFall plantingAverage last and first frost
JanFebMarAprMayJunJulAugSepOctNovDec
Boise CityMar 13–Apr 3
MeridianMar 13–Apr 3
NampaMar 18–Apr 8
CaldwellMar 18–Apr 8
Idaho FallsMar 28–Apr 18
PocatelloMar 21–Apr 11
Coeur d'AleneMar 11–Apr 1
Twin FallsMar 19–Apr 9
Post FallsMar 11–Apr 1
RexburgMar 31–Apr 21
LewistonFeb 23–Mar 16
EagleMar 18–Apr 8
KunaMar 13–Apr 3
StarMar 18–Apr 8
AmmonMar 28–Apr 18

Questions

When should I plant onions in Idaho?

In Boise City, plant out from March 13 to April 3. Across Idaho the window opens between February 23 and March 31, depending on the local last frost.

How is this date worked out?

Start seeds indoors 8–12 weeks before the last frost; plant out 3–6 weeks before the last frost. Frost dates are NOAA 1991–2020 averages for the weather station nearest each city.

More for Idaho

Onions in other states

Frost dates for every city in Idaho