Newcastle, WY frost dates
Last spring frostMay 13median date
First fall frostOct 3median date
Growing season143 daysfrost-free
Hardiness zone4bZone 4b
How Newcastle compares
- In 8 years out of 10, the last spring frost in Newcastle falls between April 30 and May 26, a 26-day window. The first fall frost falls between September 17 and October 16.
- The median last frost is 8 days earlier than the Wyoming median of May 21.
- Its 143-day growing season is longer than 88% of the 153 Wyoming places with a regular frost season (state median 125 days).
- The last frost is 5 days later than the zone 4b median of May 8. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 4b chart.
- The weather station records an average of 168 nights a year at or below 32°F.
- Compared with Rapid City, SD, 81 km away, the last frost here is 10 days later than there and the growing season is 15 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 30 |
| 50% (median) | May 13 |
| 10% (safe for tender plants) | May 26 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 17 |
| 50% (median) | October 3 |
| 90% (late) | October 16 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Newcastle, WY
Newcastle, WY frost dates — last frost May 13, first frost Oct 3, zone 4b. whenisthelastfrost.com
Crop
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Start indoors: Feb 18 to Mar 4Transplant outside: Apr 15 to Apr 29
Start indoors: Mar 4 to Mar 18Transplant outside: May 27 to Jun 10
Start indoors: Mar 4 to Mar 18Transplant outside: May 27 to Jun 10
Start indoors: Mar 18 to Apr 1Transplant outside: May 20 to Jun 3
Start indoors: Mar 18 to Apr 1Transplant outside: Apr 22 to May 6Sow outdoors: Apr 15 to May 20Plant for fall: Aug 8 to Sep 5
Start indoors: Mar 18 to Apr 1Transplant outside: Apr 15 to Apr 29Sow outdoors: Apr 15 to Apr 29Plant for fall: Jul 25 to Aug 15
Start indoors: Mar 18 to Apr 1Transplant outside: Apr 29 to May 13Plant for fall: Jun 27 to Jul 18
Start indoors: Mar 18 to Apr 1Transplant outside: Apr 22 to May 6Plant for fall: Jun 27 to Jul 18
Start indoors: Mar 18 to Apr 1Transplant outside: Apr 29 to May 13Plant for fall: Jun 27 to Jul 18
Start indoors: Apr 1 to Apr 15Transplant outside: Jun 3 to Jun 17Sow outdoors: Jun 3 to Jun 17
Start indoors: Apr 1 to Apr 15Transplant outside: May 20 to Jun 3
Sow outdoors: Apr 1 to Apr 22Plant for fall: Jul 11 to Aug 1
Sow outdoors: Apr 1 to Apr 22Plant for fall: Aug 8 to Aug 29
Sow outdoors: Apr 8 to May 20Plant for fall: Aug 22 to Sep 12
Start indoors: Apr 15 to Apr 22Transplant outside: May 27 to Jun 3Sow outdoors: May 20 to Jun 3Plant for fall: Jul 18 to Aug 1
Start indoors: Apr 15 to Apr 22Sow outdoors: May 20 to Jun 3Plant for fall: Jul 25 to Aug 8
Start indoors: Apr 15 to Apr 22Sow outdoors: May 20 to Jun 3
Start indoors: Apr 15 to Apr 22Transplant outside: May 27 to Jun 10
Sow outdoors: Apr 22 to May 20Plant for fall: Jul 11 to Jul 25
Sow outdoors: Apr 22 to May 20Plant for fall: Jul 25 to Aug 8
Sow outdoors: Apr 22 to May 13
Sow outdoors: Apr 29 to May 27Plant for fall: Jul 25 to Aug 8
Sow outdoors: Apr 29 to May 20Plant for fall: Aug 8 to Aug 29
Sow outdoors: May 20 to Jun 10Plant for fall: Jul 18 to Aug 1
Sow outdoors: May 20 to Jun 3
Transplant outside: May 27 to Jun 17
Plant for fall: Sep 19 to Oct 24
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Newcastle, WY
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 18 – Mar 4 | Apr 15 – Apr 29 | — | — |
| Peppers | Mar 4 – Mar 18 | May 27 – Jun 10 | — | — |
| Eggplant | Mar 4 – Mar 18 | May 27 – Jun 10 | — | — |
| Tomatoes | Mar 18 – Apr 1 | May 20 – Jun 3 | — | — |
| Lettuce | Mar 18 – Apr 1 | Apr 22 – May 6 | Apr 15 – May 20 | Aug 8 – Sep 5 |
| Kale | Mar 18 – Apr 1 | Apr 15 – Apr 29 | Apr 15 – Apr 29 | Jul 25 – Aug 15 |
| Broccoli | Mar 18 – Apr 1 | Apr 29 – May 13 | — | Jun 27 – Jul 18 |
| Cabbage | Mar 18 – Apr 1 | Apr 22 – May 6 | — | Jun 27 – Jul 18 |
| Cauliflower | Mar 18 – Apr 1 | Apr 29 – May 13 | — | Jun 27 – Jul 18 |
| Okra | Apr 1 – Apr 15 | Jun 3 – Jun 17 | Jun 3 – Jun 17 | — |
| Basil | Apr 1 – Apr 15 | May 20 – Jun 3 | — | — |
| Peas | — | — | Apr 1 – Apr 22 | Jul 11 – Aug 1 |
| Spinach | — | — | Apr 1 – Apr 22 | Aug 8 – Aug 29 |
| Radishes | — | — | Apr 8 – May 20 | Aug 22 – Sep 12 |
| Cucumbers | Apr 15 – Apr 22 | May 27 – Jun 3 | May 20 – Jun 3 | Jul 18 – Aug 1 |
| Zucchini & Summer Squash | Apr 15 – Apr 22 | — | May 20 – Jun 3 | Jul 25 – Aug 8 |
| Winter Squash & Pumpkins | Apr 15 – Apr 22 | — | May 20 – Jun 3 | — |
| Melons & Watermelon | Apr 15 – Apr 22 | May 27 – Jun 10 | — | — |
| Carrots | — | — | Apr 22 – May 20 | Jul 11 – Jul 25 |
| Beets | — | — | Apr 22 – May 20 | Jul 25 – Aug 8 |
| Potatoes | — | — | Apr 22 – May 13 | — |
| Swiss Chard | — | — | Apr 29 – May 27 | Jul 25 – Aug 8 |
| Cilantro | — | — | Apr 29 – May 20 | Aug 8 – Aug 29 |
| Green Beans | — | — | May 20 – Jun 10 | Jul 18 – Aug 1 |
| Sweet Corn | — | — | May 20 – Jun 3 | — |
| Sweet Potatoes | — | May 27 – Jun 17 | — | — |
| Garlic | — | — | — | Sep 19 – Oct 24 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Newcastle, WY weather station, 3 km away (elevation 4,416 ft (1,346 m)).
Frost dates near Newcastle
- Osage May 20 · Sep 23
- Four Corners May 13 · Oct 3
- Upton May 20 · Sep 23
- Sundance May 21 · Sep 25
- Beulah May 17 · Sep 27
- Moorcroft May 23 · Sep 20
- Devils Tower May 23 · Sep 20
- Alva May 17 · Sep 23
- Rozet May 15 · Oct 1
- Lance Creek May 17 · Sep 25
Frequently asked questions
When is the last frost in Newcastle, WY?
The median last spring frost in Newcastle, WY is May 13. There is still about a 10% chance of frost after May 26, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Newcastle, WY?
The median first fall frost is October 3, with about a 10% chance of frost before September 17.
How long is the growing season in Newcastle, WY?
About 143 days between the median last spring frost and first fall frost.
What planting zone is Newcastle, WY?
Newcastle, WY is in USDA hardiness zone 4b.