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

Planting zone for Castine, ME

Castine, ME is in USDA zone 5b across its 2 ZIP codes. The median last spring frost is May 7 and the first fall frost October 5.

Castine on the zone map

Outlined: its 1 ZIP code areas · 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.

Zone5b−15 to −10 °F
ZIP codes2
Last frostMay 7
First frostOct 5
Growing season151 days

5b 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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 Castine, ME

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 7median — 50% chance of a later frost
Safe for tender plantsMay 21only 10% chance of frost after
First fall frostOctober 5median — 10% chance by Sep 24
Growing season151 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 27 and returns around October 19.

From the NOAA station Belfast, ME, elevation 20 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 Castine

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 26 – Apr 9
SpinachSow outdoors · Mar 26 – Apr 16
Broccoli, cabbageStart indoors · Feb 26 – Mar 12
Broccoli, cabbageTransplant · Apr 16 – Apr 30
Onion setsPlant outdoors · Apr 9 – Apr 23
PotatoesPlant outdoors · Apr 16 – Apr 30
LettuceSow outdoors · Apr 9 – Apr 23
Carrots, beetsSow outdoors · Apr 16 – Apr 30
TomatoesStart indoors · Mar 12 – Mar 26
TomatoesTransplant · May 14 – May 28
Peppers, eggplantStart indoors · Feb 26 – Mar 12
Peppers, eggplantTransplant · May 21 – Jun 4
BeansSow outdoors · May 14 – May 28
Sweet cornSow outdoors · May 14 – May 28
Cucumbers, squashSow outdoors · May 14 – May 28
Fall lettuce, spinachSow outdoors · Aug 10 – Aug 24
GarlicPlant cloves · Sep 21 – Oct 26
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 7) and first fall frost (Oct 5) 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 04420 came on Apr 22 — about the same time as the 1991–2020 average (Apr 22).

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 5b in Maine

493 plants native to the lower 48 states, recorded in Maine, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Trees 55

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 98

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falpine bearberry0.5 ft · blooms early spring · medium shade tolerance · to −62 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °F

Wildflowers & perennials 169

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °F

Grasses 153

alpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °FAmerican beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °FAmerican cupscale3 ft · blooms early summer · high shade tolerance · to −18 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °F

Vines 6

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °FVirginia creeper1 ft · blooms late spring · medium shade tolerance · to −28 °F

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 Castine, ME.

Soil in Castine, ME

The soil mapped at the center of ZIP 04420 is Scantic — silt loam, poorly drained.

TextureSilt loama good balance for most vegetables
pH6.0slightly acidic; most vegetables like 6.0–7.0
DrainagePoorly drainedconsider raised beds
Organic matter6%high
Hydrologic groupDwater soaks in very slowly
Farmland classFarmland of local importanceUSDA classification

Map unit: Scantic silt 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 04420; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Castine, ME

Summer high77 °Faverage high, July
Winter low10 °Faverage low, January
Hot days2days a year at 90 °F or more
Freezing nights162nights a year at 32 °F or less
Growing degree days1,802base 50 °F — the season’s usable heat
Longest day15 h 32 mindaylight on June 21
Shortest day8 h 50 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation48.8 inper year, rain and melted snow
Snowfall72 inper year

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 30 °F, low 10 °F 30°10° JanFebruary: average high 32 °F, low 12 °F 32°12° FebMarch: average high 40 °F, low 20 °F 40°20° MarApril: average high 52 °F, low 31 °F 52°31° AprMay: average high 63 °F, low 41 °F 63°41° MayJune: average high 72 °F, low 51 °F 72°51° JunJuly: average high 77 °F, low 57 °F 77°57° JulAugust: average high 76 °F, low 56 °F 76°56° AugSeptember: average high 70 °F, low 48 °F 70°48° SepOctober: average high 57 °F, low 38 °F 57°38° OctNovember: average high 46 °F, low 29 °F 46°29° NovDecember: average high 35 °F, low 18 °F 35°18° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″6″January: 3.94 in precipitation, 19.2 in snowfall 3.9❄19 JanFebruary: 3.16 in precipitation, 22.4 in snowfall 3.2❄22 FebMarch: 4.12 in precipitation, 11.7 in snowfall 4.1❄12 MarApril: 4.38 in precipitation, 2.2 in snowfall 4.4❄2 AprMay: 3.86 in precipitation 3.9 MayJune: 4.28 in precipitation 4.3 JunJuly: 3.17 in precipitation 3.2 JulAugust: 3.06 in precipitation 3.1 AugSeptember: 4.09 in precipitation 4.1 SepOctober: 5.38 in precipitation, 0.3 in snowfall 5.4 OctNovember: 4.69 in precipitation, 2.5 in snowfall 4.7❄3 NovDecember: 4.65 in precipitation, 13.2 in snowfall 4.7❄13 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Belfast, ME (9 mi away); precipitation: Belfast, ME (9 mi away). Daylight is calculated from latitude.

ZIP codes in Castine

044205b
−15 to −10 °F
044215b
−15 to −10 °F

Maine planting zones →

Questions about Castine

What planting zone is Castine, ME?

Castine, ME is in USDA hardiness zone 5b on the 2023 map (5b: −15 to −10 °F).

When is the last frost in Castine, ME?

The median last spring frost is May 7 and the median first fall frost is October 5 (NOAA 1991–2020 normals, Belfast station).

When can I plant a garden in Castine, ME?

Cool-season crops like peas and spinach go in around Mar 26 – Apr 16; tomatoes, peppers, beans and squash after about May 14, once frost risk has passed.

What kind of onions grow in Castine, ME?

Long-day onions: the longest day is 15 h 32 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does Castine, ME get?

About 48.8 inches of precipitation a year and 72 inches of snowfall (NOAA 1991–2020 normals).