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

Planting zone for 06266 — South Windham, CT

ZIP code 06266 (South Windham, Southeastern Connecticut County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 28 and the first fall frost October 13.

Where ZIP 06266 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 28
First frostOct 13
2012 zone6a

Was 6a on the 2012 map — half a zone warmer now. 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 South Windham, 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 South Windham, CT

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 28median — 50% chance of a later frost
Safe for tender plantsMay 11only 10% chance of frost after
First fall frostOctober 13median — 10% chance by Oct 2
Growing season167 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 14 and returns around October 25.

From the NOAA station Willimantic Windham Airport, CT — 5 miles away, elevation 246 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 06266

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 17 – Mar 31
SpinachSow outdoors · Mar 17 – Apr 7
Broccoli, cabbageStart indoors · Feb 17 – Mar 3
Broccoli, cabbageTransplant · Apr 7 – Apr 21
Onion setsPlant outdoors · Mar 31 – Apr 14
PotatoesPlant outdoors · Apr 7 – Apr 21
LettuceSow outdoors · Mar 31 – Apr 14
Carrots, beetsSow outdoors · Apr 7 – Apr 21
TomatoesStart indoors · Mar 3 – Mar 17
TomatoesTransplant · May 5 – May 19
Peppers, eggplantStart indoors · Feb 17 – Mar 3
Peppers, eggplantTransplant · May 12 – May 26
BeansSow outdoors · May 5 – May 19
Sweet cornSow outdoors · May 5 – May 19
Cucumbers, squashSow outdoors · May 5 – May 19
Fall lettuce, spinachSow outdoors · Aug 18 – Sep 1
GarlicPlant cloves · Sep 29 – Nov 3
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 28) and first fall frost (Oct 13) 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 06266 came on Apr 3 — 3 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 South Windham, CT.

Soil in South Windham, CT

The soil mapped at the center of ZIP 06266 is Canton — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding
pH4.3strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter5.75%high
Hydrologic groupBwater soaks in moderately
Farmland classprime farmlandUSDA classification

Map unit: Canton and Charlton fine sandy loams, 3 to 8 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 06266; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in South Windham, CT

Summer high83 °Faverage high, July
Winter low18 °Faverage low, January
Hot days11days a year at 90 °F or more
Freezing nights135nights a year at 32 °F or less
Growing degree days2,758base 50 °F — the season’s usable heat
Longest day15 h 12 mindaylight on June 21
Shortest day9 h 09 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation43.3 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 36 °F, low 18 °F 36°18° JanFebruary: average high 39 °F, low 19 °F 39°19° FebMarch: average high 47 °F, low 27 °F 47°27° MarApril: average high 59 °F, low 37 °F 59°37° AprMay: average high 70 °F, low 47 °F 70°47° MayJune: average high 78 °F, low 56 °F 78°56° JunJuly: average high 83 °F, low 62 °F 83°62° JulAugust: average high 81 °F, low 60 °F 81°60° AugSeptember: average high 74 °F, low 52 °F 74°52° SepOctober: average high 63 °F, low 41 °F 63°41° OctNovember: average high 52 °F, low 31 °F 52°31° NovDecember: average high 41 °F, low 24 °F 41°24° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.20 in precipitation 3.2 JanFebruary: 2.66 in precipitation 2.7 FebMarch: 3.95 in precipitation 4.0 MarApril: 3.97 in precipitation 4.0 AprMay: 3.40 in precipitation 3.4 MayJune: 3.87 in precipitation 3.9 JunJuly: 2.66 in precipitation 2.7 JulAugust: 4.37 in precipitation 4.4 AugSeptember: 4.11 in precipitation 4.1 SepOctober: 3.83 in precipitation 3.8 OctNovember: 3.55 in precipitation 3.5 NovDecember: 3.68 in precipitation 3.7 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Willimantic Windham Airport, CT (5 mi away); precipitation: Willimantic Windham Airport, CT (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

062806b
Windham, CT · 3 mi
062266b
Willimantic, CT · 3 mi
062646b
Scotland, CT · 4 mi
062546b
North Franklin, CT · 4 mi
062566b
North Windham, CT · 4 mi
062496b
Lebanon, CT · 4 mi
063306b
Baltic, CT · 6 mi
063506b
Hanover, CT · 6 mi

Connecticut planting zones →

Questions about 06266

What planting zone is ZIP code 06266?

ZIP code 06266 (South Windham, 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 South Windham, CT?

The median last spring frost (32 °F) near 06266 is April 28; after May 11 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Willimantic Windham Airport station.

When is the first frost in South Windham, CT?

The median first fall frost near 06266 is October 13, giving a median frost-free growing season of 167 days.

When should I plant tomatoes in 06266?

Start tomato seeds indoors around Mar 3 – Mar 17 and set transplants outside around May 5 – May 19, one to three weeks after the median last frost.

How much rain and snow does 06266 get?

About 43.3 inches of precipitation a year (NOAA 1991–2020 normals, Willimantic Windham Airport station).

How hot do summers get in South Windham, CT?

The average high peaks at 83 °F in July, with about 11 days a year at 90 °F or more.

What kind of soil does 06266 have?

The USDA soil survey maps Canton at the center of ZIP 06266: fine sandy loam, well drained, pH about 4.3 (strongly acidic).

Did spring come early in South Windham, CT in 2026?

Spring leaf-out near 06266 came on Apr 3 in 2026, 3 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.

What kind of onions grow in South Windham, CT?

Long-day onions: the longest day near 06266 is 15 h 12 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 06266 change?

Yes. The 2012 USDA map put 06266 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.