USDA Hardiness Zone 6b
Frost Dates for 06488 — Southbury, Connecticut
NOAA 1991–2020 normals from Ansonia 1 NE, CT (136 ft), 11 miles southeast.
Updated
In Southbury, the last spring frost (32°F) is around April 25 in half of years and has passed by May 10 in nine years out of ten. The first fall frost comes around October 17, as early as October 4 one year in ten, leaving a typical freeze-free season of 175 days (NOAA, Ansonia 1 NE, CT).
- Last spring frost
- April 25
- First fall frost
- October 17
- Growing season
- 175 days
- Hardiness zone
- 6b
50% probability
50% probability
freeze-free, 50%
-5 to 0°F (-20.6 to -17.8°C) coldest night
- First snow
- November 30
- Last snow
- March 25
- Winters with snow
- 100%
- Snow per year
- 46.8"
median, 1991–2020
median, 1991–2020
18 of 18 observed
NOAA normal
Frost risk by date in Southbury
Half of springs at Ansonia 1 NE, CT see their last 32°F night by April 25; only one in ten is past it by April 11, and one in ten still has one after May 10. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 10 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 50% of the 28 Connecticut stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 17 in half of years, as early as October 4 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 13 days later, around October 30; in spring the one-in-ten date for 28°F is April 27, 13 days before the 32°F one. The freeze-free season lasts 175 days in a typical year, shorter than at 54% of the 28 Connecticut stations; it reaches 197 days one year in ten and falls short of 153 one year in ten. On average 130 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 13 days longer, to about May 8, and return around October 7. Severe cold of 16°F or below comes every winter, usually between December 5 and March 11.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 24 | Apr 29 | May 2 | May 5 | May 8 | May 10 | May 14 | May 17 | May 22 |
| 32°F | Apr 11 | Apr 14 | Apr 18 | Apr 22 | Apr 25 | Apr 29 | May 2 | May 6 | May 10 |
| 28°F | Mar 30 | Apr 2 | Apr 5 | Apr 7 | Apr 10 | Apr 13 | Apr 16 | Apr 20 | Apr 27 |
| 24°F | Mar 15 | Mar 20 | Mar 24 | Mar 28 | Mar 30 | Apr 1 | Apr 3 | Apr 5 | Apr 10 |
| 20°F | Mar 5 | Mar 10 | Mar 14 | Mar 17 | Mar 20 | Mar 23 | Mar 26 | Mar 30 | Apr 1 |
| 16°F | Feb 22 | Feb 28 | Mar 4 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 21 | Mar 25 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 27 | Oct 1 | Oct 3 | Oct 5 | Oct 7 | Oct 9 | Oct 13 | Oct 16 | Oct 21 |
| 32°F | Oct 4 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 27 | Nov 1 |
| 28°F | Oct 14 | Oct 19 | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 8 | Nov 13 |
| 24°F | Oct 26 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 14 | Nov 18 | Nov 23 | Nov 30 |
| 20°F | Nov 9 | Nov 14 | Nov 17 | Nov 21 | Nov 25 | Nov 28 | Dec 1 | Dec 4 | Dec 10 |
| 16°F | Nov 20 | Nov 26 | Nov 30 | Dec 2 | Dec 5 | Dec 8 | Dec 11 | Dec 16 | Dec 24 |
Freeze probabilities 1991–2020 at Ansonia 1 NE, CT, 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 06488 →Compare Southbury with another place →
Compared with the next station
The nearest other station, Danbury, CT, 12 miles southwest of Southbury and 269 feet higher, has a last frost 5 days earlier (April 20), a first frost 3 days later (October 20), a season 6 days longer.
When it snows in Southbury, Connecticut
The first measurable snow (0.1 inch or more) in Southbury usually arrives around November 30, and the last of the season around March 25. Those are the middle dates across the winters of 1991–2020 at Woodbury, CT, 5.4 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 31 days after the last snow.
Planting calendar for 06488
| When | What to do |
|---|---|
| February 14 – February 28 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 28 – March 14 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 28 – April 11 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 25 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 25 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 3 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 17 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 06488 is 11 miles from Ansonia 1 NE, CT, which stands at 136 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 11 other ZIP codes share the station; its figures are presented in full for 06484 (Shelton). The 2023 USDA Plant Hardiness Zone Map lists ZIP 06488 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across Connecticut →
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.