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

Planting zone for 06388 — West Mystic, CT

ZIP code 06388 (West Mystic, Southeastern Connecticut County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 8 and the first fall frost November 2.

Where ZIP 06388 is

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.

Zone7a0 to 5 °F

Coldest night−17.8 to −15 °C

Last frostApr 8

First frostNov 2

2012 zone6b

Was 6b 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 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for West Mystic, 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 West Mystic, CT

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostApril 8median — 50% chance of a later frost

Safe for tender plantsApril 22only 10% chance of frost after

First fall frostNovember 2median — 10% chance by Oct 18

Growing season207 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 29 and returns around November 14.

From the NOAA station Groton, CT — 3 miles away, elevation 39 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 06388

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 25 – Mar 11

SpinachSow outdoors · Feb 25 – Mar 18

Broccoli, cabbageStart indoors · Jan 28 – Feb 11

Broccoli, cabbageTransplant · Mar 18 – Apr 1

Onion setsPlant outdoors · Mar 11 – Mar 25

PotatoesPlant outdoors · Mar 18 – Apr 1

LettuceSow outdoors · Mar 11 – Mar 25

Carrots, beetsSow outdoors · Mar 18 – Apr 1

TomatoesStart indoors · Feb 11 – Feb 25

TomatoesTransplant · Apr 15 – Apr 29

Peppers, eggplantStart indoors · Jan 28 – Feb 11

Peppers, eggplantTransplant · Apr 22 – May 6

BeansSow outdoors · Apr 15 – Apr 29

Sweet cornSow outdoors · Apr 15 – Apr 29

Cucumbers, squashSow outdoors · Apr 15 – Apr 29

Fall lettuce, spinachSow outdoors · Sep 7 – Sep 21

GarlicPlant cloves · Oct 19 – Nov 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 8) and first fall frost (Nov 2) 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 06388 came on Apr 6 — 3 days later than the 1991–2020 average (Apr 3).

average
Apr 32026
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).

Soil in West Mystic, CT

The soil mapped at the center of ZIP 06388 is Agawam — fine sandy loam, well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding

pH5.4strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3.35%moderate

Hydrologic groupBwater soaks in moderately

Farmland classprime farmlandUSDA classification

Map unit: Agawam fine sandy loam, 0 to 3 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 06388; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in West Mystic, CT

Summer high81 °Faverage high, July

Winter low24 °Faverage low, January

Hot days3days a year at 90 °F or more

Freezing nights102nights a year at 32 °F or less

Growing degree days2,990base 50 °F — the season’s usable heat

Longest day15 h 10 mindaylight on June 21

Shortest day9 h 11 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation48.9 inper year, rain and melted snow

Snowfall25 inper year; 21 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Groton, CT (3 mi away); precipitation: Groton, CT (3 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

063557a

Mystic, CT · 2 mi

063727a

Old Mystic, CT · 3 mi

063407a

Groton, CT · 3 mi

063907a

Fishers Island, NY · 4 mi

063787a

Stonington, CT · 4 mi

063207a

New London, CT · 7 mi

Connecticut planting zones →

Questions about 06388

What planting zone is ZIP code 06388?

ZIP code 06388 (West Mystic, CT) is in USDA hardiness zone 7a on the 2023 map: the coldest night of an average winter reaches 0 to 5 °F (−17.8 to −15 °C).

When is the last frost in West Mystic, CT?

The median last spring frost (32 °F) near 06388 is April 8; after April 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Groton station.

When is the first frost in West Mystic, CT?

The median first fall frost near 06388 is November 2, giving a median frost-free growing season of 207 days.

When should I plant tomatoes in 06388?

Start tomato seeds indoors around Feb 11 – Feb 25 and set transplants outside around Apr 15 – Apr 29, one to three weeks after the median last frost.

How much rain and snow does 06388 get?

About 48.9 inches of precipitation a year and 25 inches of snowfall (NOAA 1991–2020 normals, Groton station).

How hot do summers get in West Mystic, CT?

The average high peaks at 81 °F in July, with about 3 days a year at 90 °F or more.

What kind of soil does 06388 have?

The USDA soil survey maps Agawam at the center of ZIP 06388: fine sandy loam, well drained, pH about 5.4 (strongly acidic).

Did spring come early in West Mystic, CT in 2026?

Spring leaf-out near 06388 came on Apr 6 in 2026, 3 days later than the 1991–2020 average (Apr 3), according to the USA National Phenology Network Spring Index.

What kind of onions grow in West Mystic, CT?

Long-day onions: the longest day near 06388 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 06388 change?

Yes. The 2012 USDA map put 06388 in zone 6b; the 2023 map puts it in zone 7a. The newer map uses 1991–2020 data and more weather stations.