Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 06231 — Amston, CT

ZIP code 06231 (Amston, Capitol Region 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 06231 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 Amston, 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 Amston, 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 — 12 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 06231

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 06231 came on Apr 3 — 5 days earlier than the 1991–2020 average (Apr 8).

average
Apr 82026
Apr 3

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.

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 Amston, CT.

Soil in Amston, CT

The soil mapped at the center of ZIP 06231 is Catden — muck, very poorly drained.

TextureMucktop layer

DrainageVery poorly drainedconsider raised beds

Organic matter82%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classNot prime farmlandUSDA classification

Map unit: Catden and Freetown soils, 0 to 2 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 06231; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Amston, 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

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Willimantic Windham Airport, CT (12 mi away); precipitation: Willimantic Windham Airport, CT (12 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

064746b

North Westchester, CT · 4 mi

062486b

Hebron, CT · 4 mi

064476b

Marlborough, CT · 4 mi

062376b

Columbia, CT · 5 mi

064156b

Colchester, CT · 6 mi

East Hampton, CT · 9 mi

Connecticut planting zones →

Questions about 06231

What planting zone is ZIP code 06231?

ZIP code 06231 (Amston, 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 Amston, CT?

The median last spring frost (32 °F) near 06231 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 Amston, CT?

The median first fall frost near 06231 is October 13, giving a median frost-free growing season of 167 days.

When should I plant tomatoes in 06231?

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 06231 get?

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

How hot do summers get in Amston, 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 06231 have?

The USDA soil survey maps Catden at the center of ZIP 06231: muck, very poorly drained.

Did spring come early in Amston, CT in 2026?

Spring leaf-out near 06231 came on Apr 3 in 2026, 5 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Amston, CT?

Long-day onions: the longest day near 06231 is 15 h 12 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 06231 change?

Yes. The 2012 USDA map put 06231 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.