USDA Hardiness Zone 5a
Frost Dates for 03285 — Thornton, New Hampshire
NOAA 1991–2020 normals from Waterville Valley Nepp, NH (1,429 ft), 6 miles east.
Updated
In Thornton, the last spring frost (32°F) is around May 15 in half of years and has passed by May 29 in nine years out of ten. The first fall frost comes around September 28, as early as September 13 one year in ten, leaving a typical freeze-free season of 134 days (NOAA, Waterville Valley Nepp, NH).
- Last spring frost
- May 15
- First fall frost
- September 28
- Growing season
- 134 days
- Hardiness zone
- 5a
50% probability
50% probability
freeze-free, 50%
-20 to -15°F (-28.9 to -26.1°C) coldest night
- First snow
- November 18
- Last snow
- April 5
- Winters with snow
- 100%
- Snow per year
- 68.3"
median, 1991–2020
median, 1991–2020
17 of 17 observed
NOAA normal
Frost risk by date in Thornton
Half of springs at Waterville Valley Nepp, NH see their last 32°F night by May 15; only one in ten is past it by May 3, and one in ten still has one after May 29. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 25 20%, and after May 29 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 25% of the 51 New Hampshire stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 28 in half of years, as early as September 13 one year in ten, and holds off past October 11 one year in ten. A hard freeze of 28°F follows 11 days later, around October 9; in spring the one-in-ten date for 28°F is May 14, 15 days before the 32°F one. The freeze-free season lasts 134 days in a typical year, shorter than at 80% of the 51 New Hampshire stations; it reaches 150 days one year in ten and falls short of 115 one year in ten. On average 188 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 14 days longer, to about May 29, and return around September 16. Severe cold of 16°F or below comes every winter, usually between November 20 and March 31.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 16 | May 20 | May 23 | May 26 | May 29 | May 31 | Jun 3 | Jun 6 | Jun 11 |
| 32°F | May 3 | May 7 | May 10 | May 13 | May 15 | May 18 | May 21 | May 25 | May 29 |
| 28°F | Apr 22 | Apr 25 | Apr 29 | Apr 30 | May 2 | May 4 | May 7 | May 10 | May 14 |
| 24°F | Apr 6 | Apr 10 | Apr 13 | Apr 17 | Apr 19 | Apr 22 | Apr 24 | Apr 28 | May 1 |
| 20°F | Mar 28 | Apr 1 | Apr 2 | Apr 4 | Apr 6 | Apr 9 | Apr 12 | Apr 15 | Apr 19 |
| 16°F | Mar 17 | Mar 21 | Mar 26 | Mar 29 | Mar 31 | Apr 1 | Apr 3 | Apr 5 | Apr 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 8 | Sep 11 | Sep 14 | Sep 16 | Sep 19 | Sep 22 | Sep 25 | Sep 30 |
| 32°F | Sep 13 | Sep 18 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 11 |
| 28°F | Sep 26 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 17 | Oct 21 | Oct 29 |
| 24°F | Oct 9 | Oct 15 | Oct 19 | Oct 23 | Oct 26 | Oct 30 | Nov 1 | Nov 4 | Nov 10 |
| 20°F | Oct 24 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 12 | Nov 14 | Nov 18 | Nov 23 |
| 16°F | Nov 8 | Nov 12 | Nov 14 | Nov 18 | Nov 20 | Nov 23 | Nov 26 | Nov 30 | Dec 5 |
Freeze probabilities 1991–2020 at Waterville Valley Nepp, NH, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 03285 →Compare Thornton with another place →
Compared with the next station
The nearest other station, Plymouth, NH, 10 miles south of Thornton and 769 feet lower, has a last frost 5 days later (May 20), a first frost 1 day earlier (September 27), a season 6 days shorter.
When it snows in Thornton, New Hampshire
The first measurable snow (0.1 inch or more) in Thornton usually arrives around November 18, and the last of the season around April 5. Those are the middle dates across the winters of 1991–2020 at Plymouth, NH, 10.2 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 40 days after the last snow.
Planting calendar for 03285
| When | What to do |
|---|---|
| March 6 – March 20 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 20 – April 3 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 17 – May 1 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 15 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 6 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 14 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 28 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 03285 is 6 miles from Waterville Valley Nepp, NH, which stands at 1,429 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 03285 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across New Hampshire →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.