First and last frost dates in Lyman, WY
At the selected station, the median last spring freeze is June 14. The median first fall freeze is September 9. 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 Lyman
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 28: 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 | May 17 – May 24 | Plan tomatoes → |
| Peppers | 8–10 weeks | Apr 19 – May 3 | Plan peppers → |
| Eggplant | 8–10 weeks | Apr 19 – May 3 | Plan eggplant → |
| Broccoli | 4–6 weeks | May 17 – May 31 | Plan broccoli → |
| Lettuce | 2–4 weeks | May 31 – Jun 14 | Plan lettuce → |
| Cucumbers | 3–5 weeks | May 24 – Jun 7 | 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 | June 14 | September 9 | 87 days |
| 30% — lower risk | June 21 | September 3 | 74 days |
| 10% — more cautious | July 1 | August 23 | 53 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 Lyman?
The median last 32°F spring freeze at the selected station is June 14. The more cautious 10% date is July 1. 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.