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

Planting zone for Portsmouth, NH

Portsmouth, NH is in USDA zone 6a across its 4 ZIP codes. The median last spring frost is May 4 and the first fall frost October 8.

Portsmouth 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.

Zone6a−10 to −5 °F
ZIP codes4
Last frostMay 4
First frostOct 8
Growing season157 days

6a 4 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 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, 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 Portsmouth

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 03802 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 03802 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 03802; 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.

ZIP codes in Portsmouth

038016a
−10 to −5 °F
038026a
−10 to −5 °F
038036a
−10 to −5 °F
038046a
−10 to −5 °F

New Hampshire planting zones →

Questions about Portsmouth

What planting zone is Portsmouth, NH?

Portsmouth, NH is in USDA hardiness zone 6a on the 2023 map (6a: −10 to −5 °F).

When is the last frost in Portsmouth, NH?

The median last spring frost is May 4 and the median first fall frost is October 8 (NOAA 1991–2020 normals, Greenland station).

When can I plant a garden in Portsmouth, NH?

Cool-season crops like peas and spinach go in around Mar 23 – Apr 13; tomatoes, peppers, beans and squash after about May 11, once frost risk has passed.

What kind of onions grow in Portsmouth, NH?

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

How much rain and snow does Portsmouth, NH get?

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