What does USDA hardiness zone 4a mean in Vermont?

Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 3 locations in Vermont fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Vermont's zone 4a is the growing season longest?

Derby Line runs the longest season on this page at about 138 days; Beecher Falls is shortest at about 121 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 Vermont's zone 4a?

Using Island Pond's frost dates (this page's median-season location): start seeds indoors about Mar 24 – Apr 7, then transplant outside about May 26 – Jun 2. 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 Vermont's zone 4a 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 3 locations listed (see the table above for each location's own dates).

USDA zone 4a in Vermont

−30 to −25 °F avg. annual extreme minimum · 3 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4a covers 3 locations across Vermont (average annual extreme minimum −30 to −25 °F): Beecher Falls, VT, Derby Line, VT, Island Pond, VT. Average last spring frost across this group ranges May 14 (Derby Line) to May 25 (Beecher Falls), and growing seasons run 121–138 days (Beecher Falls to Derby Line) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Vermont location's own frost dates; the printable planting calendar uses Island Pond, this group's median-season location.

USDA zone: 4a−30 to −25 °F
Last frost range: May 14–May 25avg, 32°F
First frost range: Sep 24–Sep 30avg, 32°F
Growing season range: 121–138days

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)
Beecher Falls	—	First Connecticut Lake	May 25	Sep 24	121
Derby Line	—	Newport	May 14	Sep 30	138
Island Pond *	—	Island Pond	May 19	Sep 29	129

* Island Pond 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 (Island Pond, representative)

Computed from Island Pond's average frost dates — the median-season location in this Vermontzone 4a 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 Island Pond (Vermont, zone 4a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 24 – Apr 7	May 26 – Jun 2	Jul 25 – Aug 14	—	matures comfortably
Pepper	Very tender	Mar 10 – Mar 24	Jun 2 – Jun 9	Aug 1 – Aug 31	—	matures comfortably
Cucumber	Tender	Apr 21 – Apr 28	May 26 – Jun 2	Jul 15 – Aug 4	—	matures comfortably
Summer squash / zucchini	Tender	—	May 26 – Jun 2	Jul 10 – Jul 25	—	matures comfortably
Bush bean	Tender	—	May 26 – Jun 2	Jul 15 – Jul 25	Jul 31 – Aug 10	matures comfortably
Sweet corn	Tender	—	May 19 – Jun 2	Jul 18 – Aug 17	—	matures comfortably
Basil	Very tender	Apr 7 – Apr 21	May 26 – Jun 2	Jun 25 – Jul 10	—	matures comfortably
Lettuce	Half-hardy	Apr 7 – Apr 21	Apr 21 – May 5	Jun 5 – Jun 20	Jul 17 – Aug 1	matures comfortably
Pea	Hardy	—	Apr 7 – Apr 21	Jun 1 – Jun 16	Jul 7 – Jul 22	matures comfortably
Spinach	Hardy	—	Apr 7 – Apr 21	May 17 – May 27	Jul 27 – Aug 6	matures comfortably
Carrot	Half-hardy	—	Apr 28 – May 5	Jun 27 – Jul 17	Jun 27 – Jul 17	matures comfortably
Broccoli	Half-hardy	Mar 24 – Apr 7	Apr 21 – May 5	Jun 15 – Jul 5	Jul 2 – Jul 22	matures comfortably

Which crops fit this growing season

Using Island Pond's own 129-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 (Island Pond)

From NOAA's 1991–2020 Climate Normals at station USC00434120. 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), Island Pond.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 2	Jun 16	Sep 15	Sep 30	103
32°F (freeze)	May 19	Jun 3	Sep 29	Oct 13	129
28°F	May 5	May 19	Oct 9	Oct 28	155
24°F	Apr 23	May 5	Oct 23	Nov 7	181

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 3 locations is 1,732; Island Pond's own reading is shown below.

Annual growing degree days for Island Pond (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,732	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,448	cool-season crops (brassicas, greens)

Hardiness zone 4a in Vermont

Zone 4a means an average annual extreme minimum winter temperature of about −30 to −25 °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. Vermont spans 4 hardiness zones in this dataset — see all Vermont locations for the full range, including zones4b, 5a, 5b.

Explore zone 4a in other states at zone 4a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 4a mean in Vermont?: Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 3 locations in Vermont fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Vermont's zone 4a is the growing season longest?: Derby Line runs the longest season on this page at about 138 days; Beecher Falls is shortest at about 121 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 Vermont's zone 4a?: Using Island Pond's frost dates (this page's median-season location): start seeds indoors about Mar 24 – Apr 7, then transplant outside about May 26 – Jun 2. 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 Vermont's zone 4a 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 3 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.