Danbury, Connecticut: planting zone & frost dates
Danbury is in USDA plant hardiness zone 6b, where the average coldest winter night reaches -5 to 0°F (-20.6 to -17.8°C). The typical last spring frost is around May 6 and the first fall frost around Oct 7.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 16 | Oct 1 |
| Typical planning date (30% risk) | May 6 | Oct 7 |
| Median (50%) | May 1 | Oct 14 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station DANBURY MUNI AP, CT (USW00054734), 1.9 mi (3.1 km) from the city center and 157 ft lower than the city center (-48 m). Record used for the 1991–2020 normals: 17 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Danbury
All 2 ZIP codes covering Danbury are in zone 6b.
Vegetable planting calendar for Danbury
Dates are counted from the 30%-risk frost dates above (last frost May 6, first frost Oct 7). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 11 – Mar 25 | May 13 – May 27 | — | — |
| Pepper | Feb 25 – Mar 11 | May 20 – Jun 3 | — | — |
| Lettuce | Mar 25 – Apr 8 | Apr 22 – May 13 | Apr 8 – May 20 | Jul 29 – Aug 26 |
| Green Beans | — | — | May 13 – Jun 17 | Jul 15 – Jul 29 |
| Sweet Corn | — | — | May 13 – Jun 10 | — |
| Zucchini & Summer Squash | Apr 8 – Apr 15 | May 13 – May 27 | May 13 – Jun 3 | Jul 15 – Jul 29 |
| Cucumber | Apr 8 – Apr 15 | May 20 – May 27 | May 13 – Jun 3 | Jul 15 – Jul 29 |
| Carrot | — | — | Apr 15 – May 20 | Jul 15 – Jul 29 |
| Onion | Feb 11 – Feb 25 | Apr 8 – Apr 22 | — | — |
| Potato | — | Apr 8 – Apr 29 | — | — |
| Basil | Mar 25 – Apr 8 | May 20 – Jun 3 | May 20 – Jun 10 | — |
| Spinach | — | — | Mar 25 – Apr 22 | Aug 12 – Sep 9 |
| Kale | Mar 11 – Mar 25 | Apr 8 – Apr 29 | Apr 8 – Apr 29 | Jul 29 – Aug 26 |
| Broccoli | Mar 11 – Mar 25 | Apr 22 – May 13 | — | Jul 15 – Jul 29 |
| Peas | — | — | Mar 25 – Apr 15 | Jul 29 – Aug 12 |
| Eggplant | Feb 25 – Mar 11 | May 20 – Jun 3 | — | — |
| Cabbage | Mar 11 – Mar 25 | Apr 8 – Apr 22 | — | Jul 15 – Jul 29 |
| Radish | — | — | Apr 1 – May 20 | Aug 26 – Sep 23 |
| Strawberry | — | Apr 8 – Apr 29 | — | — |
| Beets | — | — | Apr 15 – May 27 | Jul 29 – Aug 12 |
Nearby cities in Connecticut
- Norwalk — zone 7a, last frost Apr 23, first frost Oct 16
- Stamford — zone 7a, last frost Apr 23, first frost Oct 16
- Bridgeport — zone 7a, last frost Apr 9, first frost Nov 1
- Waterbury — zone 6b, last frost May 1, first frost Oct 11
- New Haven — zone 7a, last frost Apr 22, first frost Oct 20
- Hartford — zone 6b, last frost Apr 23, first frost Oct 20
More: all Connecticut cities · other zone 6b cities: Columbus, OH, Indianapolis, IN, Boston, MA, Detroit, MI, Kansas City, MO, Cincinnati, OH, Pittsburgh, PA, Buffalo, NY
Danbury gardening questions
When is the last frost in Danbury, CT?
Plan around May 6. At NOAA's Danbury Municipal Airport, CT station, 1.9 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by May 1, and after May 16 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 18. The last frost is fairly predictable here: only 28 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Danbury, CT?
Start seeds indoors Mar 11 – Mar 25 and set transplants outside May 13 – May 27, once nights stay above 50°F and the soil is near 60°F. That leaves 154 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Danbury?
About 166 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 146 days, and in 1 year in 10 it runs 187 days or more. In fall there is a 10% chance of frost by Oct 1 and a 30% chance by Oct 7. That is the shortest of the 7 Connecticut cities on this site.
When should I plant a fall garden in Danbury?
Count back from the first fall frost (Oct 7): transplant broccoli Jul 15 – Jul 29; sow kale Jul 29 – Aug 26; sow lettuce Jul 29 – Aug 26; sow radishes Aug 26 – Sep 23. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 27. How the math works: succession and fall planting.
Did Danbury's hardiness zone change on the 2023 map?
Yes. Most of Danbury was zone 6a on the 2012 map and is zone 6b on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Danbury compare with Bridgeport, CT?
Danbury is zone 6b and Bridgeport is zone 7a. The typical last spring frost in Danbury (May 6) comes about 27 days later than in Bridgeport, CT (Apr 9), 21 miles away, and the first fall frost is Oct 7 versus Nov 1. Danbury sits about 570 ft higher, which explains part of the gap. The two cities use different NOAA stations.