What does USDA hardiness zone 6b mean in Connecticut?

Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 12 locations in Connecticut fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Connecticut's zone 6b is the growing season longest?

Shelton runs the longest season on this page at about 216 days; Stafford Springs is shortest at about 159 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in Connecticut's zone 6b?

Using Manchester's frost dates (this page's median-season location): start seeds indoors about Feb 22 – Mar 8, then transplant outside about Apr 26 – May 3. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Connecticut's zone 6b have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 12 locations listed (see the table above for each location's own dates).

USDA zone 6b in Connecticut

−5 to 0 °F avg. annual extreme minimum · 12 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 6b covers 12 locations across Connecticut (average annual extreme minimum −5 to 0 °F): Bristol, CT, Danbury, CT, Manchester, CT, Mashantucket, CT, Middletown, CT, Naugatuck, CT, and 6 more. Average last spring frost across this group ranges April 5 (Shelton) to May 7 (Stafford Springs), and growing seasons run 159–216 days (Stafford Springs to Shelton) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Connecticut location's own frost dates; the printable planting calendar uses Manchester, this group's median-season location.

USDA zone: 6b−5 to 0 °F
Last frost range: Apr 5–May 7avg, 32°F
First frost range: Oct 12–Nov 6avg, 32°F
Growing season range: 159–216days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Bristol	New Britain, West Simsbury, Weatogue, Terryville, Watertown, Canton Valley	Burlington	Apr 25	Oct 18	172
Danbury	Sandy Hook, East, Ridgefield, Bethel, New Milford, Tashua, +11 more	Danbury	Apr 20	Oct 20	181
Manchester *	Crystal Lake, Storrs, Coventry Lake, Mansfield Center, Terramuggus, Lake Chaffee, +1 more	Storrs	Apr 19	Oct 22	186
Mashantucket	—	Groton	Apr 8	Nov 2	207
Middletown	Waterbury, Meriden, Naugatuck, Durham, Northford, Wallingford Center, +7 more	Meriden Markham Muni Ap	Apr 26	Oct 16	175
Naugatuck	Ansonia, Heritage, Woodbury Center	Ansonia 1 Ne	Apr 25	Oct 17	175
North Haven	Ansonia, Quinnipiac University	New Haven Tweed Ap	Apr 17	Oct 27	193
Norwich	Colchester, Oxoboxo River, Moodus, Hope Valley, Hopkinton, Chester Center, +4 more	Norwich Public Utility Plt	Apr 14	Oct 24	192
Shelton	Derby	Bridgeport Sikorsky Mem Ap	Apr 5	Nov 6	216
Stafford Springs	—	Staffordville	May 7	Oct 12	159
West Hartford	East Hartford, Hartford, New Britain, Newington, Wethersfield, Manchester, +9 more	Hartford Brainard Fld	Apr 17	Oct 26	191
Willimantic	Colchester, South Coventry, Mansfield Center, South Windham, Plainfield	Willimantic Windham Ap	Apr 28	Oct 13	167

* Manchester is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Manchester, representative)

Computed from Manchester's average frost dates — the median-season location in this Connecticutzone 6b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Manchester (Connecticut, zone 6b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Feb 22 – Mar 8	Apr 26 – May 3	Jun 25 – Jul 15	—	matures comfortably
Pepper	Very tender	Feb 8 – Feb 22	May 3 – May 10	Jul 2 – Aug 1	—	matures comfortably
Cucumber	Tender	Mar 22 – Mar 29	Apr 26 – May 3	Jun 15 – Jul 5	—	matures comfortably
Summer squash / zucchini	Tender	—	Apr 26 – May 3	Jun 10 – Jun 25	—	matures comfortably
Bush bean	Tender	—	Apr 26 – May 3	Jun 15 – Jun 25	Aug 23 – Sep 2	matures comfortably
Sweet corn	Tender	—	Apr 19 – May 3	Jun 18 – Jul 18	—	matures comfortably
Basil	Very tender	Mar 8 – Mar 22	Apr 26 – May 3	May 26 – Jun 10	—	matures comfortably
Lettuce	Half-hardy	Mar 8 – Mar 22	Mar 22 – Apr 5	May 6 – May 21	Aug 9 – Aug 24	matures comfortably
Pea	Hardy	—	Mar 8 – Mar 22	May 2 – May 17	Jul 30 – Aug 14	matures comfortably
Spinach	Hardy	—	Mar 8 – Mar 22	Apr 17 – Apr 27	Aug 19 – Aug 29	matures comfortably
Carrot	Half-hardy	—	Mar 29 – Apr 5	May 28 – Jun 17	Jul 20 – Aug 9	matures comfortably
Broccoli	Half-hardy	Feb 22 – Mar 8	Mar 22 – Apr 5	May 16 – Jun 5	Jul 25 – Aug 14	matures comfortably

Which crops fit this growing season

Using Manchester's own 186-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Manchester)

From NOAA's 1991–2020 Climate Normals at station USC00068138. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Manchester.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 3	May 16	Oct 10	Oct 25	160
32°F (freeze)	Apr 19	May 3	Oct 22	Nov 6	186
28°F	Apr 6	Apr 19	Nov 4	Nov 20	211
24°F	Mar 30	Apr 8	Nov 18	Dec 4	233

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 12 locations is 2,958; Manchester's own reading is shown below.

Annual growing degree days for Manchester (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	2,683	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	4,847	cool-season crops (brassicas, greens)

Hardiness zone 6b in Connecticut

Zone 6b means an average annual extreme minimum winter temperature of about −5 to 0 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Connecticut spans 5 hardiness zones in this dataset — see all Connecticut locations for the full range, including zones5b, 6a, 7a, 7b.

Explore zone 6b in other states at zone 6b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 6b mean in Connecticut?: Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 12 locations in Connecticut fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Connecticut's zone 6b is the growing season longest?: Shelton runs the longest season on this page at about 216 days; Stafford Springs is shortest at about 159 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in Connecticut's zone 6b?: Using Manchester's frost dates (this page's median-season location): start seeds indoors about Feb 22 – Mar 8, then transplant outside about Apr 26 – May 3. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Connecticut's zone 6b have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 12 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.