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Seed Starting Calendar for Idaho

Median last frost from Apr 20 to Jun 13 across Idaho

NOAA stations
124
Median last frost, Boise
Apr 24
Passed in 9 of 10 years
May 9
Last frost

Last spring frost dates in Idaho

Lowell in the Clearwater country and Coeur d'Alene reach a median last frost in mid to late April, Boise around Apr 24, and Idaho Falls on the Snake River Plain about a month later, around May 23.

Three dates per station from the NOAA 1991 to 2020 normals. The median is the date half of springs run past. The last column is the date the last 32°F night has passed by in 9 years out of 10, the one to hold tender transplants for.

StationElevationEarly (1 in 10 years later than this)Median last frostPassed in 9 of 10 yearsMedian first fall frost
Lowell Three RiversLowell Three Rivers, USW000041091,480 ftMar 26Apr 16May 4Oct 25
Coeur d'AleneCoeur D'Alene, USC001019562,133 ftApr 4Apr 22May 6Oct 18
BoiseBoise Air Terminal, USW000241312,814 ftApr 4Apr 24May 9Oct 21
Challis AirportChallis Airport, USW000041145,033 ftMay 2May 14Jun 2Sep 25
Idaho FallsIdaho Falls Fanning Field, USW000241454,729 ftMay 7May 23Jun 13Sep 20
Crop chart

When to start seeds in Idaho, spring 2027

Counted back from the median last frost at Boise, April 24. Pick another station to redraw the chart for it.

Seed starting calendar for Boise, Idaho, spring 2027JanFebMarAprMayOnion (from seed)Onion (from seed): start indoors Jan 16 to Jan 30Onion (from seed): harden off Mar 13 to Mar 27Onion (from seed): set out Mar 27 to Apr 3PepperPepper: start indoors Feb 27 to Mar 13Pepper: harden off Apr 24 to May 8Pepper: set out May 8 to May 15EggplantEggplant: start indoors Feb 27 to Mar 13Eggplant: harden off Apr 24 to May 8Eggplant: set out May 8 to May 15TomatoTomato: start indoors Mar 6 to Mar 20Tomato: harden off Apr 17 to May 1Tomato: set out May 1 to May 8BroccoliBroccoli: start indoors Feb 13 to Feb 27Broccoli: harden off Mar 13 to Mar 27Broccoli: set out Mar 27 to Apr 10CabbageCabbage: start indoors Feb 13 to Feb 27Cabbage: harden off Mar 13 to Mar 27Cabbage: set out Mar 27 to Apr 3LettuceLettuce: start indoors Feb 20 to Feb 27Lettuce: harden off Mar 13 to Mar 27Lettuce: set out Mar 27 to Apr 3BasilBasil: start indoors Mar 13 to Mar 27Basil: harden off Apr 24 to May 8Basil: set out May 8 to May 15CucumberCucumber: start indoors Apr 3 to Apr 10Cucumber: harden off Apr 17 to May 1Cucumber: set out May 1 to May 8Cucumber: sow outdoors Apr 24 to May 1Summer squashSummer squash: start indoors Apr 10 to Apr 17Summer squash: harden off Apr 24 to May 8Summer squash: set out May 8 to May 15Summer squash: sow outdoors Apr 24 to May 1PeasPeas: sow outdoors Mar 27 to Apr 10CarrotCarrot: sow outdoors Apr 10 to Apr 24BeansBeans: sow outdoors Apr 24 to May 1Sweet cornSweet corn: sow outdoors Apr 24 to May 1Median last frost Apr 249 in 10 years May 9
Start indoorsHarden offSet outSow outdoorsMedian last frostLast freeze passed in 9 of 10 years
Every crop, counted from a median last frost of April 24
CropStart indoorsSet outSow outdoorsFrost class
TomatoMar 6 to Mar 20May 1 to May 8Tender, very tender
PepperFeb 27 to Mar 13May 8 to May 15Tender, very tender
EggplantFeb 27 to Mar 13May 8 to May 15Tender, very tender
BasilMar 13 to Mar 27May 8 to May 15Tender
CeleryJan 30 to Feb 13Apr 24 to May 1Tender
CucumberApr 3 to Apr 10May 1 to May 8Apr 24 to May 1Tender
Summer squashApr 10 to Apr 17May 8 to May 15Apr 24 to May 1Tender
Winter squashApr 10 to Apr 17May 8 to May 15May 8 to May 15Tender, very tender
PumpkinApr 10 to Apr 17May 8 to May 15May 8 to May 15Tender, very tender
Melon (cantaloupe)Apr 10 to Apr 17May 8 to May 15Tender, very tender
WatermelonApr 3 to Apr 17May 8 to May 15Tender, very tender
Onion (from seed)Jan 16 to Jan 30Mar 27 to Apr 3Hardy
LeekJan 16 to Jan 30Mar 27 to Apr 3Hardy
ParsleyJan 23 to Jan 30Apr 3 to Apr 10Half-hardy
BroccoliFeb 13 to Feb 27Mar 27 to Apr 10Hardy
Brussels sproutsFeb 13 to Feb 27Mar 27 to Apr 10Hardy
CabbageFeb 13 to Feb 27Mar 27 to Apr 3Hardy
CauliflowerFeb 27 to Mar 13Apr 10 to Apr 17Half-hardy
KaleFeb 13 to Feb 27Mar 27 to Apr 3Hardy
LettuceFeb 20 to Feb 27Mar 27 to Apr 3Hardy
Swiss chardFeb 27 to Mar 13Apr 10 to Apr 17Mar 27 to Apr 3Half-hardy
SpinachJan 30 to Feb 13Mar 13 to Apr 3Mar 27 to Apr 10Hardy
PeasMar 27 to Apr 10Hardy
RadishMar 27 to Apr 10Hardy
CarrotApr 10 to Apr 24Half-hardy
BeetApr 10 to Apr 24Half-hardy
BeansApr 24 to May 1Tender
Sweet cornApr 24 to May 1Tender
Six square pots of dark compost seen from above, each holding a single seedling with two narrow seed leaves
Tomato seedlings at the seed leaf stage, one to a pot. The University of Minnesota Extension holds off on fertilizer until a seedling has several sets of true leaves, then feeds at quarter strength once a week. “Tomato Seedlings (49768696597)” by Amanda Slater from Coventry, West Midlands, UK, CC BY-SA 2.0
Extension guide

What University of Idaho Extension advises

University of Idaho Extension publishes the planting guide Idaho gardeners work from, Idaho Master Gardener Handbook, Chapter 20: Principles of Vegetable Culture.

“Figure 10. Planting and transplanting guide for vegetable crops based on the date of the last spring frost. On the bar, zero (0) is the date of the last spring frost, as determined for your locale. Each number to the right or left is the number of weeks before (-) or after (+) the average last frost.”
University of Idaho Extension, Idaho Master Gardener Handbook, Chapter 20: Principles of Vegetable Culture, quoted exactly.
“Once you know the anticipated date of transplanting, see Table 6 to find the number of weeks needed to produce transplants of your chosen crops. Then count backward from the transplanting date”
University of Idaho Extension, Idaho Master Gardener Handbook, Chapter 20: Producing and Establishing Transplants, quoted exactly.
“Cole crops (cabbage, broccoli, cauliflower, kale, brussels sprouts, etc.) and onions: Transplant 2–3 weeks before the average last frost.”
University of Idaho Extension, on broccoli, quoted exactly.
“Three to four weeks before the average last spring frost: Plant cold-hardy crops, including onions, peas, kale, cabbage, broccoli, and cauliflower. (The last three can be transplanted within the same time frame.)”
University of Idaho Extension, on cabbage, quoted exactly.
“Cole crops (cabbage, broccoli, cauliflower, kale, brussels sprouts, etc.) and onions: Transplant 2–3 weeks before the average last frost.”
University of Idaho Extension, on onion, quoted exactly.
“Most salad crops (lettuce, Swiss chard, spinach, etc.): Transplant a week or so before the average last frost.”
University of Idaho Extension, on lettuce, quoted exactly.
A gardener kneeling beside a raised bed setting a young tomato plant into dark soil, an empty nursery pot beside her
Setting out a tomato in June at a community garden. Tender crops go out after the last frost, and after a week or two of hardening off outdoors. “Volunteer planting heirloom tomato (4704185147)”, Pacific Southwest Region 5, Public domain

Seed starting questions for Idaho

Frost dates from NOAA NCEI U.S. Climate Normals 1991-2020, annual/seasonal, by station (v1.0.1). Planting guidance from University of Idaho Extension, quoted exactly. Seed starting weeks from UNH Cooperative Extension. Compiled 2026-09-21.

First frost in IdahoThe other end of the season: when fall frost ends the tender crops.Soil temperatureBeans, corn and squash sown direct wait on warm soil as well as the last frost.Idaho lawn care calendarSpring seeding, feeding and mowing dates on the same climate.Fall planting calendarGarlic, cool season crops and a second sowing window in the fall.Frost dates by ZIPFirst and last frost odds for any address.

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