Idaho Frost Dates
Published: February 1, 2026 · Updated: April 23, 2026
Last Spring Frost
April 15
Zone 5a
First Fall Frost
October 15
Zone 5a
Frost-Free Season
183 days
Mid-April to Mid-November
Lawn Care Timing for Idaho
Vegetable Garden Timing for Idaho
Frost Dates by City in Idaho
Frequently Asked Questions
What is the last frost date in Idaho?
The average last spring frost in Idaho (zone 5a) is April 15. Dates vary by city and elevation. Find your specific city below for exact dates.
When is it safe to plant tomatoes in Idaho?
Transplant tomato seedlings outdoors after April 15 — the average last frost date for zone 5a. Start seeds indoors Early February (10 weeks before last frost). Wait 2 weeks after last frost for extra safety.
When should I overseed my lawn in Idaho?
The prime overseeding window in Idaho is August 25–September 20. This ensures 6 weeks of warm soil for germination before the first fall frost on October 15.
When should I apply winteriser in Idaho?
Apply winteriser fertiliser by Mid-November. Your first fall frost of October 15 is the hard deadline — apply at least 2–3 weeks before.
What USDA zone is Idaho?
Idaho contains USDA zones 4b, 5a. Each zone has different frost dates and growing seasons. Find your city below for your specific zone.