First and last frost dates in Ashton, ID
At the selected station, the median last spring freeze is May 21. The median first fall freeze is September 21. 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 Ashton
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 Jun 8: 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 27 – May 4 | Plan tomatoes → |
| Peppers | 8–10 weeks | Mar 30 – Apr 13 | Plan peppers → |
| Eggplant | 8–10 weeks | Mar 30 – Apr 13 | Plan eggplant → |
| Broccoli | 4–6 weeks | Apr 27 – May 11 | Plan broccoli → |
| Lettuce | 2–4 weeks | May 11 – May 25 | Plan lettuce → |
| Cucumbers | 3–5 weeks | May 4 – May 18 | 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 21 | September 21 | 123 days |
| 30% — lower risk | June 1 | September 13 | 104 days |
| 10% — more cautious | June 13 | September 4 | 83 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 Ashton?
The median last 32°F spring freeze at the selected station is May 21. The more cautious 10% date is June 13. 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.