First and last frost dates in Ammon, ID
At the selected station, the median last spring freeze is May 9. The median first fall freeze is October 1. Compare the 10%, 30% and 50% historical freeze probabilities below.
Spring and fall freeze dates
32°F / 0°CA 30% risk date leaves a smaller historical chance of a later spring freeze than the median. It is not a forecast or a guarantee.
Plan planting dates in Ammon
Select a freeze probability
The 10% date is a more cautious spring starting point. Tender crops may need warmer soil and nights too.
Calculate when to start seeds
Use the number of weeks on your seed packet to work backwards from a suitable outdoor date.
Check the local forecast
A normal describes the past. Check this year’s forecast before moving plants outdoors.
Indoor seed-starting dates by crop
Work backwards from an outdoor target of May 24: the selected spring freeze date plus an editable seven-day delay.
These are transplant-growing windows, not a recommendation to plant every crop on the same day. Adjust the outdoor target for your crop, soil temperature and local conditions.
| Crop | Time indoors | Illustrative sowing window | Your plan |
|---|---|---|---|
| Tomatoes | 5–6 weeks | Apr 12 – Apr 19 | Plan tomatoes → |
| Peppers | 8–10 weeks | Mar 15 – Mar 29 | Plan peppers → |
| Eggplant | 8–10 weeks | Mar 15 – Mar 29 | Plan eggplant → |
| Broccoli | 4–6 weeks | Apr 12 – Apr 26 | Plan broccoli → |
| Lettuce | 2–4 weeks | Apr 26 – May 10 | Plan lettuce → |
| Cucumbers | 3–5 weeks | Apr 19 – May 3 | Plan cucumbers → |
Indoor durations: University of Maryland Extension. The seven-day delay is our example, not the university’s prescription. Your seed packet takes priority.
Calculate fall planting dates
Compare your seed packet’s days to maturity with the time before your selected fall freeze date.
Freeze dates by probability
Download these dates| Historical probability | Last spring freeze on or after | First fall freeze on or before | Interval |
|---|---|---|---|
| 50% — median | May 9 | October 1 | 145 days |
| 30% — lower risk | May 17 | September 25 | 131 days |
| 10% — more cautious | June 2 | September 17 | 107 days |
“Frost date” is common gardening shorthand. These NOAA figures describe air temperatures reaching 32°F; frost on leaves can occur under different conditions. The two tail probabilities do not give the probability of a completely freeze-free season.
Frost date questions
How we use the dataWhen is the last frost in Ammon?
The median last 32°F spring freeze at the selected station is May 9. The more cautious 10% date is June 2. Neither date predicts the weather in a particular year.
Can I plant tomatoes on the last frost date?
Use the date as one input. Tomatoes need warm soil, suitable nighttime temperatures, and hardening off. A 50% historical date still carries substantial freeze risk. Check your seed instructions, local extension guidance and current forecast.
Why do other websites show a different date?
Sites may use another station, reference period, temperature threshold or probability. This guide identifies the station and shows three probabilities so you can compare like with like.