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

Planting zone for 03803 — Portsmouth, NH

ZIP code 03803 (Portsmouth, Rockingham County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 4 and the first fall frost October 8.

Where ZIP 03803 is

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.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 4
First frostOct 8
2012 zone6a

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Portsmouth, NH…

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 Portsmouth, NH

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 4median — 50% chance of a later frost
Safe for tender plantsMay 18only 10% chance of frost after
First fall frostOctober 8median — 10% chance by Sep 27
Growing season157 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 23 and returns around October 21.

From the NOAA station Greenland, NH — 5 miles away, elevation 95 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 03803

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 23 – Apr 6
SpinachSow outdoors · Mar 23 – Apr 13
Broccoli, cabbageStart indoors · Feb 23 – Mar 9
Broccoli, cabbageTransplant · Apr 13 – Apr 27
Onion setsPlant outdoors · Apr 6 – Apr 20
PotatoesPlant outdoors · Apr 13 – Apr 27
LettuceSow outdoors · Apr 6 – Apr 20
Carrots, beetsSow outdoors · Apr 13 – Apr 27
TomatoesStart indoors · Mar 9 – Mar 23
TomatoesTransplant · May 11 – May 25
Peppers, eggplantStart indoors · Feb 23 – Mar 9
Peppers, eggplantTransplant · May 18 – Jun 1
BeansSow outdoors · May 11 – May 25
Sweet cornSow outdoors · May 11 – May 25
Cucumbers, squashSow outdoors · May 11 – May 25
Fall lettuce, spinachSow outdoors · Aug 13 – Aug 27
GarlicPlant cloves · Sep 24 – Oct 29
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 4) and first fall frost (Oct 8) 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 03803 came on Apr 12 — about the same time as the 1991–2020 average (Apr 14).

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 6a in New Hampshire

486 plants native to the lower 48 states, recorded in New Hampshire, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 53

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 99

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 171

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °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 °F

Grasses 142

alpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °FAmerican beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °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 °FBebb's sedge3 ft · blooms late spring · low shade tolerance · to −38 °F

Vines 7

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 creeper2 ft · blooms summer · high shade tolerance · to −13 °Ftrumpet honeysuckle16 ft · blooms late summer · low shade tolerance · to −33 °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 Portsmouth, NH.

Soil in Portsmouth, NH

The soil mapped at the center of ZIP 03803 is Canton — gravelly fine sandy loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureGravelly fine sandy loamdrains and warms fast; dries out and needs more feeding
pH4.8strongly acidic; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter4%moderate
Hydrologic groupAwater soaks in fast
Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Canton complex, 3 to 15 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 03803; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Portsmouth, NH

Summer high81 °Faverage high, July
Winter low16 °Faverage low, January
Hot days11days a year at 90 °F or more
Freezing nights143nights a year at 32 °F or less
Growing degree days2,385base 50 °F — the season’s usable heat
Longest day15 h 22 mindaylight on June 21
Shortest day9 h 00 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation49.4 inper year, rain and melted snow
Snowfall56 inper year; 66 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 33 °F, low 16 °F 33°16° JanFebruary: average high 36 °F, low 18 °F 36°18° FebMarch: average high 43 °F, low 25 °F 43°25° MarApril: average high 56 °F, low 35 °F 56°35° AprMay: average high 66 °F, low 45 °F 66°45° MayJune: average high 75 °F, low 54 °F 75°54° JunJuly: average high 81 °F, low 60 °F 81°60° JulAugust: average high 79 °F, low 59 °F 79°59° AugSeptember: average high 72 °F, low 52 °F 72°52° SepOctober: average high 60 °F, low 41 °F 60°41° OctNovember: average high 48 °F, low 31 °F 48°31° NovDecember: average high 38 °F, low 22 °F 38°22° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 3.39 in precipitation, 15.9 in snowfall 3.4❄16 JanFebruary: 3.53 in precipitation, 16.2 in snowfall 3.5❄16 FebMarch: 4.58 in precipitation, 10.5 in snowfall 4.6❄11 MarApril: 4.71 in precipitation, 1.2 in snowfall 4.7❄1 AprMay: 3.97 in precipitation 4.0 MayJune: 4.32 in precipitation 4.3 JunJuly: 3.85 in precipitation 3.9 JulAugust: 3.60 in precipitation 3.6 AugSeptember: 4.00 in precipitation 4.0 SepOctober: 4.83 in precipitation, 0.1 in snowfall 4.8 OctNovember: 3.97 in precipitation, 0.9 in snowfall 4.0❄1 NovDecember: 4.67 in precipitation, 11 in snowfall 4.7❄11 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Greenland, NH (5 mi away); precipitation: Eliot, ME (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

038026a
Portsmouth, NH · <1 mi
038046a
Portsmouth, NH · <1 mi
038016a
Portsmouth, NH · 2 mi
038546a
New Castle, NH · 2 mi
039046a
Kittery, ME · 3 mi
038706a
Rye, NH · 4 mi
038406a
Greenland, NH · 5 mi
039036a
Eliot, ME · 5 mi

All 4 ZIP codes in Portsmouth → · New Hampshire planting zones →

Questions about 03803

What planting zone is ZIP code 03803?

ZIP code 03803 (Portsmouth, NH) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Portsmouth, NH?

The median last spring frost (32 °F) near 03803 is May 4; after May 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Greenland station.

When is the first frost in Portsmouth, NH?

The median first fall frost near 03803 is October 8, giving a median frost-free growing season of 157 days.

When should I plant tomatoes in 03803?

Start tomato seeds indoors around Mar 9 – Mar 23 and set transplants outside around May 11 – May 25, one to three weeks after the median last frost.

How much rain and snow does 03803 get?

About 49.4 inches of precipitation a year and 56 inches of snowfall (NOAA 1991–2020 normals, Eliot station).

How hot do summers get in Portsmouth, NH?

The average high peaks at 81 °F in July, with about 11 days a year at 90 °F or more.

What kind of soil does 03803 have?

The USDA soil survey maps Canton at the center of ZIP 03803: gravelly fine sandy loam, well drained, pH about 4.8 (strongly acidic).

Did spring come early in Portsmouth, NH in 2026?

Spring leaf-out near 03803 came on Apr 12 in 2026, about the same as the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Portsmouth, NH?

Long-day onions: the longest day near 03803 is 15 h 22 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).