What USDA hardiness zone is Portland-South Portland, ME?

Portland-South Portland, ME spans USDA hardiness zones 5a to 6b. 43% of its ZIP codes are zone 6a, so there is no single zone for the metro.

When is the last spring frost in Portland-South Portland, ME?

The median last spring freeze runs April 26 – May 16 across the 20 NOAA weather stations serving Portland-South Portland, ME, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Place guide

Planting zones in Portland-South Portland, ME

This metro spans USDA zones 5a to 6b, so there is no single zone for Portland-South Portland, ME and anyone who gives you one is rounding. 43% of its ZIP codes are zone 6a; the rest are not.

USDA zones 5a–6b 4 zones across 81 ZIP codes

ZIP codes 81 81 have a NOAA station within range

Weather stations 20 NOAA 1991–2020 normals, across 2,081 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Portland-South Portland, ME as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.

The growing season in Portland-South Portland, ME is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 30 – October 21 across the 20 NOAA stations serving this metro area .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around March 1 – March 21 — counted back from a last spring freeze of April 26 – May 16 here.

Every spring date for your ZIP →

These are ranges across the whole metro area. The ZIP lookup above gives the dates from your own nearest station instead.

All 20 stations agreeAt least one station

Every one of the 20 NOAA stations serving this metro area counts May 16 – September 30 as growing season (137 days). Widening to any single station gives April 26 – October 21 (178 days).

That is a 41-day difference inside one metro area — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.

Which zone you are in depends where you are

Portland-South Portland, ME covers 4 hardiness zones. A guide that gives the metro one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 43% in zone 6a and wrong for the other 57%. Here is the actual split.

Zone	ZIP codes	Share
6a	35	43%
5b	33	41%
5a	12	15%
6b	1	1%

Zones are published per ZIP code, so yours is exact even though the metro's is not. The hardiness tool will tell you which one you are in.

Your freeze dates

Last spring freeze April 26 – May 16

First fall freeze September 30 – October 21

Those are the earliest and latest medians among the 20 stations serving this metro — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.

The spread is the point. Even in a metro that is one hardiness zone throughout, its stations disagree about the last spring freeze. Hardiness zone and frost date measure different things — a zone is the average annual coldest night, a freeze date is when the season turns — and a place can be uniform in one and varied in the other. Use the tools below with your own ZIP rather than the ends of this range.

Your growing season

NOAA publishes a growing-season length for each station, and across the 20 stations serving Portland-South Portland, ME it runs 136–175 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 74–80 °F , below the 90 °F point where cool-season crops reliably bolt. Summer rain over the same months runs 10.6–13.1" across those 20 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. The middle station covers about 92% of it, so expect to make up the rest. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 77 °F summer afternoon drying the soil faster than a cool one.

When to start seeds in Portland-South Portland, ME

Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 20 stations — the earliest and latest that job falls anywhere in the metro — because no one station speaks for the whole area.

Crop	Job	When	Offset
Green Onions	Start indoors	March 1 – March 21	8 weeks before
Peppers	Start indoors	March 1 – March 21	8 weeks before
Broccoli	Start indoors	March 15 – April 4	6 weeks before
Cabbage	Start indoors	March 15 – April 4	6 weeks before
Collards	Start indoors	March 15 – April 4	6 weeks before
Kale	Start indoors	March 15 – April 4	6 weeks before
Leaf Lettuce	Start indoors	March 15 – April 4	6 weeks before
Peas	Direct sow	March 15 – April 4	6 weeks before
Spinach	Direct sow	March 15 – April 4	6 weeks before
Sweet Potato	Start indoors	March 15 – April 4	6 weeks before
Tomatoes	Start indoors	March 15 – April 4	6 weeks before
Bok Choy	Start indoors	March 22 – April 11	5 weeks before
Kohlrabi	Start indoors	March 22 – April 11	5 weeks before
Swiss Chard	Start indoors	March 22 – April 11	5 weeks before
Arugula	Direct sow	March 29 – April 18	4 weeks before
Baby Salad Greens	Direct sow	March 29 – April 18	4 weeks before
Beets	Direct sow	March 29 – April 18	4 weeks before
Green Onions	Direct sow	March 29 – April 18	4 weeks before
Mustard Greens	Direct sow	March 29 – April 18	4 weeks before
Okra	Start indoors	March 29 – April 18	4 weeks before
Radishes	Direct sow	March 29 – April 18	4 weeks before
Turnips	Direct sow	March 29 – April 18	4 weeks before
Cabbage	Set out	April 5 – April 25	3 weeks before
Carrots	Direct sow	April 5 – April 25	3 weeks before
Collards	Direct sow	April 5 – April 25	3 weeks before
Collards	Set out	April 5 – April 25	3 weeks before
Cucumbers	Start indoors	April 5 – April 25	3 weeks before
Green Onions	Set out	April 5 – April 25	3 weeks before
Kale	Direct sow	April 5 – April 25	3 weeks before
Kale	Set out	April 5 – April 25	3 weeks before
Kohlrabi	Direct sow	April 5 – April 25	3 weeks before
Kohlrabi	Set out	April 5 – April 25	3 weeks before
Leaf Lettuce	Direct sow	April 5 – April 25	3 weeks before
Pumpkins	Start indoors	April 5 – April 25	3 weeks before
Summer Squash	Start indoors	April 5 – April 25	3 weeks before
Winter Squash	Start indoors	April 5 – April 25	3 weeks before
Zucchini	Start indoors	April 5 – April 25	3 weeks before
Bok Choy	Direct sow	April 12 – May 2	2 weeks before
Bok Choy	Set out	April 12 – May 2	2 weeks before
Broccoli	Set out	April 12 – May 2	2 weeks before
Cilantro	Direct sow	April 12 – May 2	2 weeks before
Leaf Lettuce	Set out	April 12 – May 2	2 weeks before
Swiss Chard	Direct sow	April 12 – May 2	2 weeks before
Swiss Chard	Set out	April 12 – May 2	2 weeks before
Dill	Direct sow	April 19 – May 9	1 week before
Bush Beans	Direct sow	May 3 – May 23	1 week after
Cucumbers	Set out	May 3 – May 23	1 week after
Pumpkins	Direct sow	May 3 – May 23	1 week after
Pumpkins	Set out	May 3 – May 23	1 week after
Summer Squash	Direct sow	May 3 – May 23	1 week after
Summer Squash	Set out	May 3 – May 23	1 week after
Sweet Corn	Direct sow	May 3 – May 23	1 week after
Tomatoes	Set out	May 3 – May 23	1 week after
Winter Squash	Direct sow	May 3 – May 23	1 week after
Winter Squash	Set out	May 3 – May 23	1 week after
Zucchini	Direct sow	May 3 – May 23	1 week after
Zucchini	Set out	May 3 – May 23	1 week after
Cucumbers	Direct sow	May 10 – May 30	2 weeks after
Okra	Direct sow	May 10 – May 30	2 weeks after
Okra	Set out	May 10 – May 30	2 weeks after
Peppers	Set out	May 10 – May 30	2 weeks after
Southern Peas	Direct sow	May 10 – May 30	2 weeks after
Sweet Potato	Set out	May 10 – May 30	2 weeks after

The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.

What survives the winter changes across Portland-South Portland, ME

Of 74 perennial fruits, nuts, berries, vegetables and herbs, 51 come through the winter in zone 6a and only 48 in zone 5a. That is a different garden at each end of the same metro.

Zone	ZIPs	Survive
5a	12	48 of 74
5b	33	48 of 74
6a	35	51 of 74
6b	1	51 of 74

The last column is the counterintuitive one, and it is why the totals do not simply rise as the winters get milder. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the summer heat that comes with it. See the full list with reasons.

Cautious — shortens the seasonMedian across stationsOptimistic

Last spring freeze: Plan to May 29 to be careful. Median April 26 – May 16 across 20 stations; April 15 is the optimistic end.
First fall freeze: Plan to September 16 to be careful. Median September 30 – October 21 across 20 stations; November 4 is the optimistic end.

NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.

The 20 stations behind these numbers

All 20 NOAA stations whose normals this page quotes, spanning about 133 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole metro area.

A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.

Every figure above comes from these, and each is named so you can check it. Which station serves a given ZIP code, and how far away it is, varies across the metro — the table below gives it per ZIP code rather than this page averaging it.

Station	NOAA ID	Last spring freeze	First fall freeze	Season
Bath, ME	USC00170409	May 10	October 6	149 days
Bridgton 3 NW, ME	USC00170844	May 5	October 5	151 days
Brunswick Nas, ME	USW00014611	May 2	October 10	160 days
Cape Neddick, ME	USC00171131	May 1	October 14	165 days
Durham 2 N, NH	USW00054794	May 3	October 10	158 days
Durham, ME	USC00172048	May 15	October 2	139 days
East Hiram, ME	USC00172238	May 12	October 1	140 days
Gardiner, ME	USC00173046	May 1	October 11	163 days
Gray, ME	USC00173295	April 28	October 19	172 days
Greenland, NH	USC00273626	May 4	October 8	157 days
Hollis, ME	USC00173862	May 14	September 30	136 days
Kennebunkport, ME	USC00174193	May 9	October 3	146 days
Poland, ME	USC00176856	May 3	October 7	157 days
Portland INTL Jetport, ME	USW00014764	April 26	October 15	170 days
Rochester Skyhaven AP, NH	USW00054791	April 30	October 9	161 days
Sanford 2 Nnw, ME	USC00177479	May 16	September 30	136 days
West Buxton 2 Nnw, ME	USC00179314	May 7	October 4	148 days
Westport Island, ME	USC00179547	April 28	October 21	175 days
Windham 2Nw, ME	USC00179720	April 30	October 20	172 days
Wiscasset AP, ME	USW00094623	May 8	October 7	151 days

These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.

Every ZIP code in Portland-South Portland, ME

Zones are published per ZIP code, not per metro area, so this is the exact answer rather than the metro area's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.

ZIP code	USDA zone	Nearest NOAA station	Distance
03901	6a	Rochester Skyhaven AP, NH	6.9 km
03902	6a	Cape Neddick, ME	1.3 km
03903	6a	Durham 2 N, NH	12.8 km
03904	6a	Greenland, NH	12.4 km
03905	6b	Greenland, NH	18.1 km
03906	5b	Sanford 2 Nnw, ME	11.7 km
03907	6a	Cape Neddick, ME	4.2 km
03908	6a	Cape Neddick, ME	9.2 km
03909	6a	Cape Neddick, ME	7.2 km
03910	6a	Cape Neddick, ME	6.2 km
03911	6a	Cape Neddick, ME	9.8 km
04001	5b	Sanford 2 Nnw, ME	15.6 km
04002	5b	Sanford 2 Nnw, ME	10.2 km
04003	6a	Brunswick Nas, ME	18.7 km
04005	5b	Kennebunkport, ME	14.7 km
04008	5b	Bath, ME	12.5 km
04009	5a	Bridgton 3 NW, ME	2.5 km
04011	5b	Brunswick Nas, ME	3.2 km
04015	5b	Windham 2Nw, ME	11.2 km
04017	6a	Portland INTL Jetport, ME	20.0 km
04019	6a	Portland INTL Jetport, ME	15.9 km
04020	5a	East Hiram, ME	13.2 km
04021	5b	Gray, ME	11.2 km
04024	5a	East Hiram, ME	7.2 km
04027	5b	Sanford 2 Nnw, ME	12.5 km
04029	5a	East Hiram, ME	8.0 km
04030	5b	Hollis, ME	6.7 km
04032	6a	Brunswick Nas, ME	14.0 km
04038	5b	West Buxton 2 Nnw, ME	12.1 km
04039	5b	Gray, ME	9.2 km
04040	5a	Bridgton 3 NW, ME	10.2 km
04042	5b	Hollis, ME	5.2 km
04043	5b	Kennebunkport, ME	9.0 km
04046	6a	Kennebunkport, ME	7.7 km
04047	5b	East Hiram, ME	19.7 km
04048	5a	Hollis, ME	9.7 km
04049	5a	West Buxton 2 Nnw, ME	9.5 km
04050	6a	Portland INTL Jetport, ME	12.5 km
04055	5a	Bridgton 3 NW, ME	13.5 km
04056	5b	Hollis, ME	14.8 km
04057	5a	Bridgton 3 NW, ME	4.6 km
04061	5a	Hollis, ME	5.7 km
04062	5b	Windham 2Nw, ME	8.5 km
04063	6a	Kennebunkport, ME	16.7 km
04064	6a	Portland INTL Jetport, ME	15.6 km
04066	6a	Brunswick Nas, ME	15.2 km
04069	5b	Gray, ME	5.9 km
04071	5b	Windham 2Nw, ME	4.6 km
04072	5b	Portland INTL Jetport, ME	17.3 km
04073	5b	Sanford 2 Nnw, ME	6.1 km
04074	6a	Portland INTL Jetport, ME	8.5 km
04076	5b	Sanford 2 Nnw, ME	11.5 km
04079	6a	Brunswick Nas, ME	12.7 km
04083	5b	Sanford 2 Nnw, ME	2.8 km
04084	5b	West Buxton 2 Nnw, ME	9.1 km
04085	5a	West Buxton 2 Nnw, ME	10.2 km
04086	5b	Brunswick Nas, ME	7.4 km
04087	5b	Hollis, ME	10.4 km
04090	6a	Cape Neddick, ME	11.9 km
04091	5a	East Hiram, ME	4.4 km
04092	5b	Portland INTL Jetport, ME	7.7 km
04093	5b	West Buxton 2 Nnw, ME	8.3 km
04095	5b	Hollis, ME	19.3 km
04096	6a	Gray, ME	14.0 km
04097	6a	Gray, ME	5.3 km
04101	6a	Portland INTL Jetport, ME	3.7 km
04102	6a	Portland INTL Jetport, ME	0.6 km
04103	6a	Portland INTL Jetport, ME	5.2 km
04105	6a	Portland INTL Jetport, ME	10.3 km
04106	6a	Portland INTL Jetport, ME	2.3 km
04107	6a	Portland INTL Jetport, ME	8.6 km
04108	6a	Portland INTL Jetport, ME	9.2 km
04109	6a	Portland INTL Jetport, ME	6.5 km
04110	6a	Portland INTL Jetport, ME	14.0 km
04260	5b	Poland, ME	7.6 km
04287	5b	Durham, ME	13.0 km
04357	5b	Gardiner, ME	12.0 km
04530	6a	Bath, ME	5.4 km
04548	6a	Westport Island, ME	6.9 km
04562	6a	Westport Island, ME	15.8 km
04579	5b	Wiscasset AP, ME	4.6 km

ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.

Your own ZIP

Work out your own dates

Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.

What survives my winter?
Runs on the hardiness zone, so it answers for all of Portland-South Portland, ME at once — zone across 74 perennial fruits, berries, vegetables and herbs.
When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.

Other places to compare

These metros span exactly the same zones — 5a–6b — so the same plants are in and out of range across them. The freeze dates and the spring calendar are their own.

Traverse City, MI — zones 5a–6b

Gardening in Maine — zones 3b– 7a covers the whole state: how its 424 ZIP codes divide between 8 hardiness zones, and the freeze dates across every NOAA station in it.

Other metro areas in ME:

Bangor, ME Zones 4b–5a
Lewiston-Auburn, ME Zone 5b

All 388 metro areas, by state

Gear

If you want to act on this

Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.

Trunk wrapZone 5a is cold enough that winter sun on a young trunk does more damage than the cold does.
Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
MulchFor the perennials nearest their cold limit in zone 5a, where an insulated crown is what decides whether they come back.

As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.

Sources

Where these numbers come from

The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates are NOAA's 1991–2020 Climate Normals, read from every station whose normals cover a ZIP code in this metro. Nothing here is estimated, and no station stands in for another.

This page names no single station on purpose. Picking one to represent a metro sounds reasonable and is not: the station serving the most ZIP codes is an artifact of where ZIP centroids happen to fall, and it selects a lock on the Monongahela for Pittsburgh and a far southern suburb for Chicago. A range across every station is true; a single cited date for a whole metro is not.

All metro areas