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

Planting zone for 04478 — Rockwood, ME

ZIP code 04478 (Rockwood, Somerset County) is in USDA zone 4b: the coldest winter night averages −25 to −20 °F. The median last spring frost is May 23 and the first fall frost September 29.

Where ZIP 04478 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.

Zone4b−25 to −20 °F

Coldest night−31.7 to −28.9 °C

Last frostMay 23

First frostSep 29

2012 zone4a

Was 4a 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 4b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Rockwood, ME…

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 Rockwood, ME

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 23median — 50% chance of a later frost

Safe for tender plantsJune 4only 10% chance of frost after

First fall frostSeptember 29median — 10% chance by Sep 16

Growing season128 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 9 and returns around October 10.

From the NOAA station Brassua Dam, ME — 5 miles away, elevation 1,070 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 04478

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 11 – Apr 25

SpinachSow outdoors · Apr 11 – May 2

Broccoli, cabbageStart indoors · Mar 14 – Mar 28

Broccoli, cabbageTransplant · May 2 – May 16

Onion setsPlant outdoors · Apr 25 – May 9

PotatoesPlant outdoors · May 2 – May 16

LettuceSow outdoors · Apr 25 – May 9

Carrots, beetsSow outdoors · May 2 – May 16

TomatoesStart indoors · Mar 28 – Apr 11

TomatoesTransplant · May 30 – Jun 13

Peppers, eggplantStart indoors · Mar 14 – Mar 28

Peppers, eggplantTransplant · Jun 6 – Jun 20

BeansSow outdoors · May 30 – Jun 13

Sweet cornSow outdoors · May 30 – Jun 13

Cucumbers, squashSow outdoors · May 30 – Jun 13

Fall lettuce, spinachSow outdoors · Aug 4 – Aug 18

GarlicPlant cloves · Sep 15 – Oct 20

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 23) and first fall frost (Sep 29) 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 04478 came on Apr 27 — 8 days earlier than the 1991–2020 average (May 5).

average
May 52026
Apr 27

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 4b in Maine

451 plants native to the lower 48 states, recorded in Maine, and rated by the USDA to survive −25 °F or colder — the bottom of zone 4b. 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 Rockwood, ME.

Soil in Rockwood, ME

The soil mapped at the center of ZIP 04478 is Telos — moderately decomposed plant material, somewhat poorly drained.

TextureModerately decomposed plant materialtop layer

DrainageSomewhat poorly drainedconsider raised beds

Organic matter53%high

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Telos-Monarda-Monson association, 0 to 8 percent slopes, rocky.

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 04478; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Rockwood, ME

Summer high76 °Faverage high, July

Winter low1 °Faverage low, January

Hot days1days a year at 90 °F or more

Freezing nights192nights a year at 32 °F or less

Growing degree days1,549base 50 °F — the season’s usable heat

Longest day15 h 43 mindaylight on June 21

Shortest day8 h 40 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

Snowfall108 inper year; 146 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: Brassua Dam, ME (5 mi away); precipitation: Brassua Dam, ME (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

044424b

Greenville Junction, ME · 18 mi

044414a

Greenville, ME · 22 mi

049854b

West Forks, ME · 25 mi

049454b

Jackman, ME · 27 mi

044855a

Shirley Mills, ME · 27 mi

Maine planting zones →

Questions about 04478

What planting zone is ZIP code 04478?

ZIP code 04478 (Rockwood, ME) is in USDA hardiness zone 4b on the 2023 map: the coldest night of an average winter reaches −25 to −20 °F (−31.7 to −28.9 °C).

When is the last frost in Rockwood, ME?

The median last spring frost (32 °F) near 04478 is May 23; after June 4 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Brassua Dam station.

When is the first frost in Rockwood, ME?

The median first fall frost near 04478 is September 29, giving a median frost-free growing season of 128 days.

When should I plant tomatoes in 04478?

Start tomato seeds indoors around Mar 28 – Apr 11 and set transplants outside around May 30 – Jun 13, one to three weeks after the median last frost.

How much rain and snow does 04478 get?

About 43.3 inches of precipitation a year and 108 inches of snowfall (NOAA 1991–2020 normals, Brassua Dam station).

How hot do summers get in Rockwood, ME?

The average high peaks at 76 °F in July, with about 1 days a year at 90 °F or more.

What kind of soil does 04478 have?

The USDA soil survey maps Telos at the center of ZIP 04478: moderately decomposed plant material, somewhat poorly drained.

Did spring come early in Rockwood, ME in 2026?

Spring leaf-out near 04478 came on Apr 27 in 2026, 8 days earlier than the 1991–2020 average (May 5), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Rockwood, ME?

Long-day onions: the longest day near 04478 is 15 h 43 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 04478 change?

Yes. The 2012 USDA map put 04478 in zone 4a; the 2023 map puts it in zone 4b. The newer map uses 1991–2020 data and more weather stations.