Union, NH frost dates
Last spring frostMay 16median date
First fall frostSep 30median date
Growing season137 daysfrost-free
Hardiness zone5bZone 5b
How Union compares
- In 8 years out of 10, the last spring frost in Union falls between May 2 and May 29, a 27-day window. The first fall frost falls between September 18 and October 10.
- The median last frost is 9 days later than the New Hampshire median of May 7.
- Its 137-day growing season is longer than 22% of the 252 New Hampshire places with a regular frost season (state median 150 days).
- The last frost is 15 days later than the zone 5b median of May 1. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5b chart.
- The weather station records an average of 156 nights a year at or below 32°F.
- Compared with Manchester, NH, 64 km away, the last frost here is 16 days later than there and the growing season is 27 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 2 |
| 50% (median) | May 16 |
| 10% (safe for tender plants) | May 29 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 18 |
| 50% (median) | September 30 |
| 90% (late) | October 10 |
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 Union, NH
Union, NH frost dates — last frost May 16, first frost Sep 30, zone 5b. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Feb 21 to Mar 7Transplant outside: Apr 18 to May 2
Start indoors: Mar 7 to Mar 21Transplant outside: May 30 to Jun 13
Start indoors: Mar 7 to Mar 21Transplant outside: May 30 to Jun 13
Start indoors: Mar 21 to Apr 4Transplant outside: May 23 to Jun 6
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 25 to May 9Sow outdoors: Apr 18 to May 23Plant for fall: Aug 5 to Sep 2
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 18 to May 2Sow outdoors: Apr 18 to May 2Plant for fall: Jul 22 to Aug 12
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 24 to Jul 15
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 25 to May 9Plant for fall: Jun 24 to Jul 15
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 24 to Jul 15
Start indoors: Apr 4 to Apr 18Transplant outside: Jun 6 to Jun 20Sow outdoors: Jun 6 to Jun 20
Start indoors: Apr 4 to Apr 18Transplant outside: May 23 to Jun 6
Sow outdoors: Apr 4 to Apr 25Plant for fall: Jul 8 to Jul 29
Sow outdoors: Apr 4 to Apr 25Plant for fall: Aug 5 to Aug 26
Sow outdoors: Apr 11 to May 23Plant for fall: Aug 19 to Sep 9
Start indoors: Apr 18 to Apr 25Transplant outside: May 30 to Jun 6Sow outdoors: May 23 to Jun 6Plant for fall: Jul 15 to Jul 29
Start indoors: Apr 18 to Apr 25Sow outdoors: May 23 to Jun 6Plant for fall: Jul 22 to Aug 5
Start indoors: Apr 18 to Apr 25Sow outdoors: May 23 to Jun 6
Start indoors: Apr 18 to Apr 25Transplant outside: May 30 to Jun 13
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 8 to Jul 22
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 22 to Aug 5
Sow outdoors: Apr 25 to May 16
Sow outdoors: May 2 to May 30Plant for fall: Jul 22 to Aug 5
Sow outdoors: May 2 to May 23Plant for fall: Aug 5 to Aug 26
Sow outdoors: May 23 to Jun 13Plant for fall: Jul 15 to Jul 29
Sow outdoors: May 23 to Jun 6
Transplant outside: May 30 to Jun 20
Plant for fall: Sep 16 to Oct 21
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Union, NH
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 21 – Mar 7 | Apr 18 – May 2 | — | — |
| Peppers | Mar 7 – Mar 21 | May 30 – Jun 13 | — | — |
| Eggplant | Mar 7 – Mar 21 | May 30 – Jun 13 | — | — |
| Tomatoes | Mar 21 – Apr 4 | May 23 – Jun 6 | — | — |
| Lettuce | Mar 21 – Apr 4 | Apr 25 – May 9 | Apr 18 – May 23 | Aug 5 – Sep 2 |
| Kale | Mar 21 – Apr 4 | Apr 18 – May 2 | Apr 18 – May 2 | Jul 22 – Aug 12 |
| Broccoli | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 24 – Jul 15 |
| Cabbage | Mar 21 – Apr 4 | Apr 25 – May 9 | — | Jun 24 – Jul 15 |
| Cauliflower | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 24 – Jul 15 |
| Okra | Apr 4 – Apr 18 | Jun 6 – Jun 20 | Jun 6 – Jun 20 | — |
| Basil | Apr 4 – Apr 18 | May 23 – Jun 6 | — | — |
| Peas | — | — | Apr 4 – Apr 25 | Jul 8 – Jul 29 |
| Spinach | — | — | Apr 4 – Apr 25 | Aug 5 – Aug 26 |
| Radishes | — | — | Apr 11 – May 23 | Aug 19 – Sep 9 |
| Cucumbers | Apr 18 – Apr 25 | May 30 – Jun 6 | May 23 – Jun 6 | Jul 15 – Jul 29 |
| Zucchini & Summer Squash | Apr 18 – Apr 25 | — | May 23 – Jun 6 | Jul 22 – Aug 5 |
| Winter Squash & Pumpkins | Apr 18 – Apr 25 | — | May 23 – Jun 6 | — |
| Melons & Watermelon | Apr 18 – Apr 25 | May 30 – Jun 13 | — | — |
| Carrots | — | — | Apr 25 – May 23 | Jul 8 – Jul 22 |
| Beets | — | — | Apr 25 – May 23 | Jul 22 – Aug 5 |
| Potatoes | — | — | Apr 25 – May 16 | — |
| Swiss Chard | — | — | May 2 – May 30 | Jul 22 – Aug 5 |
| Cilantro | — | — | May 2 – May 23 | Aug 5 – Aug 26 |
| Green Beans | — | — | May 23 – Jun 13 | Jul 15 – Jul 29 |
| Sweet Corn | — | — | May 23 – Jun 6 | — |
| Sweet Potatoes | — | May 30 – Jun 20 | — | — |
| Garlic | — | — | — | Sep 16 – Oct 21 |
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 Sanford 2 Nnw, ME weather station, 23 km away (elevation 289 ft (88 m)).
Frost dates near Union
- Milton Mills May 16 · Sep 30
- New Durham Apr 30 · Oct 9
- Sanbornville May 16 · Sep 30
- Milton Apr 30 · Oct 9
- Farmington Apr 30 · Oct 9
- Alton Apr 30 · Oct 18
- East Wakefield May 16 · Sep 30
- Alton Bay Apr 30 · Oct 18
- Wolfeboro Apr 30 · Oct 18
- Wolfeboro Falls Apr 30 · Oct 18
Frequently asked questions
When is the last frost in Union, NH?
The median last spring frost in Union, NH is May 16. There is still about a 10% chance of frost after May 29, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Union, NH?
The median first fall frost is September 30, with about a 10% chance of frost before September 18.
How long is the growing season in Union, NH?
About 137 days between the median last spring frost and first fall frost.
What planting zone is Union, NH?
Union, NH is in USDA hardiness zone 5b.