Idaho frost dates
Across Idaho, the average last spring frost is around May 10 and the average first fall frost around September 25 - roughly 138 frost-free days. USDA zones 3b, 4b, 5b, 6a, 6b, 7a.
Idaho spans a wide range of elevations and climates - your town’s dates can differ from the state average by two weeks or more. Look up your exact ZIP.
What these dates mean for planting in Idaho
Counted from the average frost dates above. For every crop, see the full Idaho planting calendar.
Frost dates by zone in Idaho
Idaho spans USDA zones 3b, 4b, 5b, 6a, 6b, 7a. Colder zones - usually higher or further inland - have later spring and earlier fall frosts than the state average.
Frost dates in nearby states
Questions gardeners ask
When is the last frost in Idaho?
The statewide average last spring frost is around May 10. There is still roughly a one-in-two chance of frost on that date, so for tender plants a safer date is about two weeks later, around May 24. Idaho covers a wide range of elevations and climates, so check your own ZIP code.
When is the first frost in Idaho?
The average first fall frost is around September 25. Frost-tender crops such as tomatoes, peppers, beans and squash should be harvested or covered before then; an early frost two weeks sooner, around September 11, happens in roughly one year in ten.
How long is the growing season in Idaho?
About 138 frost-free days on average between the last spring frost and the first fall frost. That is a short season, so start warm-season crops indoors and choose quick-maturing varieties.
When can I plant tomatoes outside in Idaho?
Plant tomato transplants outdoors between May 10 – May 27, once nights stay above about 50°F. Start seeds indoors six to eight weeks earlier.
Is it safe to plant on the average last frost date?
For hardy crops such as peas, spinach, onions and cabbage, yes - they handle a light frost. For tender crops, no: the average date still carries about a 50% chance of a later frost, so wait one to two weeks or keep row cover ready.
→ Turn these into sowing dates with the Idaho planting calendar, look up an exact ZIP code, or read how frost dates work. Month by month: what to plant in February · what to plant in March · what to plant in April · what to plant in May · what to plant in June · what to plant in July · what to plant in August · what to plant in September · what to plant in October · what to plant in November.
Statewide average from NOAA/NCEI freeze normals. Cautious and gambler dates are about two weeks either side of the average.