Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 06488 — Southbury, CT

ZIP code 06488 (Southbury, Naugatuck Valley County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 20 and the first fall frost October 20.

Where ZIP 06488 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone6b−5 to 0 °F
Coldest night−20.6 to −17.8 °C
Last frostApr 20
First frostOct 20
2012 zone6b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Southbury, CT…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Southbury, CT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 20median — 50% chance of a later frost
Safe for tender plantsMay 6only 10% chance of frost after
First fall frostOctober 20median — 10% chance by Oct 5
Growing season181 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 7 and returns around November 1.

From the NOAA station Danbury, CT — 11 miles away, elevation 404 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 06488

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 9 – Mar 23
SpinachSow outdoors · Mar 9 – Mar 30
Broccoli, cabbageStart indoors · Feb 9 – Feb 23
Broccoli, cabbageTransplant · Mar 30 – Apr 13
Onion setsPlant outdoors · Mar 23 – Apr 6
PotatoesPlant outdoors · Mar 30 – Apr 13
LettuceSow outdoors · Mar 23 – Apr 6
Carrots, beetsSow outdoors · Mar 30 – Apr 13
TomatoesStart indoors · Feb 23 – Mar 9
TomatoesTransplant · Apr 27 – May 11
Peppers, eggplantStart indoors · Feb 9 – Feb 23
Peppers, eggplantTransplant · May 4 – May 18
BeansSow outdoors · Apr 27 – May 11
Sweet cornSow outdoors · Apr 27 – May 11
Cucumbers, squashSow outdoors · Apr 27 – May 11
Fall lettuce, spinachSow outdoors · Aug 25 – Sep 8
GarlicPlant cloves · Oct 6 – Nov 10
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 20) and first fall frost (Oct 20) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 06488 came on Apr 2 — 4 days earlier than the 1991–2020 average (Apr 6).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 6b in Connecticut

533 plants native to the lower 48 states, recorded in Connecticut, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. Each links to its USDA PLANTS profile.

Trees 64

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 105

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °F

Wildflowers & perennials 187

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 151

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °FAtlantic mannagrass3 ft · blooms summer · low shade tolerance · to −8 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 9

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fcatbird grape30 ft · blooms late spring · medium shade tolerance · to −13 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Fheartleaf peppervine2 ft · blooms late spring · low shade tolerance · to −8 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Southbury, CT.

Soil in Southbury, CT

The soil mapped at the center of ZIP 06488 is Hollis — highly decomposed plant material, somewhat excessively drained.

TextureHighly decomposed plant materialtop layer
DrainageSomewhat excessively drainednatural drainage class
Organic matter40%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Hollis-Chatfield-Rock outcrop complex, 15 to 45 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 06488; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Southbury, CT

Summer high85 °Faverage high, July
Winter low21 °Faverage low, January
Hot days20days a year at 90 °F or more
Freezing nights126nights a year at 32 °F or less
Growing degree days3,102base 50 °F — the season’s usable heat
Longest day15 h 11 mindaylight on June 21
Shortest day9 h 10 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation51.2 inper year, rain and melted snow
Snowfall47 inper year; 49 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 36 °F, low 21 °F 36°21° JanFebruary: average high 39 °F, low 22 °F 39°22° FebMarch: average high 48 °F, low 29 °F 48°29° MarApril: average high 61 °F, low 39 °F 61°39° AprMay: average high 72 °F, low 49 °F 72°49° MayJune: average high 80 °F, low 59 °F 80°59° JunJuly: average high 85 °F, low 64 °F 85°64° JulAugust: average high 82 °F, low 63 °F 82°63° AugSeptember: average high 75 °F, low 55 °F 75°55° SepOctober: average high 63 °F, low 43 °F 63°43° OctNovember: average high 50 °F, low 34 °F 50°34° NovDecember: average high 40 °F, low 26 °F 40°26° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 3.71 in precipitation, 11.3 in snowfall 3.7❄11 JanFebruary: 3.05 in precipitation, 13.7 in snowfall 3.0❄14 FebMarch: 4.11 in precipitation, 10.3 in snowfall 4.1❄10 MarApril: 3.97 in precipitation, 1.4 in snowfall 4.0❄1 AprMay: 3.66 in precipitation 3.7 MayJune: 4.59 in precipitation 4.6 JunJuly: 4.97 in precipitation 5.0 JulAugust: 5.03 in precipitation 5.0 AugSeptember: 4.95 in precipitation 5.0 SepOctober: 4.95 in precipitation 5.0 OctNovember: 4.00 in precipitation, 1.5 in snowfall 4.0❄2 NovDecember: 4.17 in precipitation, 8.6 in snowfall 4.2❄9 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Danbury, CT (11 mi away); precipitation: Woodbury, CT (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

064876b
South Britain, CT · 1 mi
064826b
Sandy Hook, CT · 5 mi
064786b
Oxford, CT · 5 mi
067986b
Woodbury, CT · 6 mi
067626b
Middlebury, CT · 6 mi
067836b
Roxbury, CT · 6 mi
064916b
Stevenson, CT · 7 mi
064706b
Newtown, CT · 7 mi

Connecticut planting zones →

Questions about 06488

What planting zone is ZIP code 06488?

ZIP code 06488 (Southbury, CT) is in USDA hardiness zone 6b on the 2023 map: the coldest night of an average winter reaches −5 to 0 °F (−20.6 to −17.8 °C).

When is the last frost in Southbury, CT?

The median last spring frost (32 °F) near 06488 is April 20; after May 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Danbury station.

When is the first frost in Southbury, CT?

The median first fall frost near 06488 is October 20, giving a median frost-free growing season of 181 days.

When should I plant tomatoes in 06488?

Start tomato seeds indoors around Feb 23 – Mar 9 and set transplants outside around Apr 27 – May 11, one to three weeks after the median last frost.

How much rain and snow does 06488 get?

About 51.2 inches of precipitation a year and 47 inches of snowfall (NOAA 1991–2020 normals, Woodbury station).

How hot do summers get in Southbury, CT?

The average high peaks at 85 °F in July, with about 20 days a year at 90 °F or more.

What kind of soil does 06488 have?

The USDA soil survey maps Hollis at the center of ZIP 06488: highly decomposed plant material, somewhat excessively drained.

Did spring come early in Southbury, CT in 2026?

Spring leaf-out near 06488 came on Apr 2 in 2026, 4 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Southbury, CT?

Long-day onions: the longest day near 06488 is 15 h 11 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).