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

Planting zone for 03810 — Alton Bay, NH

ZIP code 03810 (Alton Bay, Belknap County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 30 and the first fall frost October 18.

Where ZIP 03810 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.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostApr 30
First frostOct 18
2012 zone5a

Was 5a 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 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Alton Bay, 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 Alton Bay, NH

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 30median — 50% chance of a later frost
Safe for tender plantsMay 13only 10% chance of frost after
First fall frostOctober 18median — 10% chance by Oct 4
Growing season170 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 17 and returns around November 1.

From the NOAA station Lakeport 2, NH — 9 miles away, elevation 499 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 03810

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 19 – Apr 2
SpinachSow outdoors · Mar 19 – Apr 9
Broccoli, cabbageStart indoors · Feb 19 – Mar 5
Broccoli, cabbageTransplant · Apr 9 – Apr 23
Onion setsPlant outdoors · Apr 2 – Apr 16
PotatoesPlant outdoors · Apr 9 – Apr 23
LettuceSow outdoors · Apr 2 – Apr 16
Carrots, beetsSow outdoors · Apr 9 – Apr 23
TomatoesStart indoors · Mar 5 – Mar 19
TomatoesTransplant · May 7 – May 21
Peppers, eggplantStart indoors · Feb 19 – Mar 5
Peppers, eggplantTransplant · May 14 – May 28
BeansSow outdoors · May 7 – May 21
Sweet cornSow outdoors · May 7 – May 21
Cucumbers, squashSow outdoors · May 7 – May 21
Fall lettuce, spinachSow outdoors · Aug 23 – Sep 6
GarlicPlant cloves · Oct 4 – Nov 8
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 30) and first fall frost (Oct 18) 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 03810 came on Apr 16 — 5 days earlier than the 1991–2020 average (Apr 21).

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 New Hampshire

475 plants native to the lower 48 states, recorded in New Hampshire, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. 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 96

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 167

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 141

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 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 Alton Bay, NH.

Soil in Alton Bay, NH

The soil mapped at the center of ZIP 03810 is Lyman — moderately decomposed plant material, somewhat excessively drained.

TextureModerately decomposed plant materialtop layer
pH3.5strongly acidic; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter85%high
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Lyman-Tunbridge-Rock outcrop complex, 35 to 60 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 03810; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Alton Bay, NH

Summer high82 °Faverage high, July
Winter low12 °Faverage low, January
Hot days9days a year at 90 °F or more
Freezing nights150nights a year at 32 °F or less
Growing degree days2,482base 50 °F — the season’s usable heat
Longest day15 h 26 mindaylight on June 21
Shortest day8 h 56 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation45.6 inper year, rain and melted snow
Snowfall62 inper year; 91 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 30 °F, low 12 °F 30°12° JanFebruary: average high 34 °F, low 13 °F 34°13° FebMarch: average high 43 °F, low 21 °F 43°21° MarApril: average high 56 °F, low 33 °F 56°33° AprMay: average high 68 °F, low 45 °F 68°45° MayJune: average high 77 °F, low 55 °F 77°55° JunJuly: average high 82 °F, low 60 °F 82°60° JulAugust: average high 81 °F, low 59 °F 81°59° AugSeptember: average high 73 °F, low 52 °F 73°52° SepOctober: average high 60 °F, low 40 °F 60°40° OctNovember: average high 47 °F, low 30 °F 47°30° NovDecember: average high 36 °F, low 20 °F 36°20° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″4″5″January: 3.08 in precipitation, 18.8 in snowfall 3.1❄19 JanFebruary: 2.88 in precipitation, 16.9 in snowfall 2.9❄17 FebMarch: 3.39 in precipitation, 9.4 in snowfall 3.4❄9 MarApril: 3.65 in precipitation, 1.6 in snowfall 3.6❄2 AprMay: 3.47 in precipitation 3.5 MayJune: 4.44 in precipitation 4.4 JunJuly: 4.61 in precipitation 4.6 JulAugust: 3.89 in precipitation 3.9 AugSeptember: 3.77 in precipitation 3.8 SepOctober: 4.83 in precipitation, 0.3 in snowfall 4.8 OctNovember: 3.68 in precipitation, 2.1 in snowfall 3.7❄2 NovDecember: 3.92 in precipitation, 12.8 in snowfall 3.9❄13 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Lakeport 2, NH (9 mi away); precipitation: Lakeport 2, NH (9 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

032495b
Gilford, NH · 4 mi
038095b
Alton, NH · 6 mi
038965b
Wolfeboro Falls, NH · 7 mi
038375b
Gilmanton Iron Works, NH · 7 mi
032375b
Gilmanton, NH · 7 mi
032985b
Tilton, NH · 8 mi
032995b
Tilton, NH · 8 mi
038555b
New Durham, NH · 8 mi

New Hampshire planting zones →

Questions about 03810

What planting zone is ZIP code 03810?

ZIP code 03810 (Alton Bay, NH) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Alton Bay, NH?

The median last spring frost (32 °F) near 03810 is April 30; after May 13 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lakeport 2 station.

When is the first frost in Alton Bay, NH?

The median first fall frost near 03810 is October 18, giving a median frost-free growing season of 170 days.

When should I plant tomatoes in 03810?

Start tomato seeds indoors around Mar 5 – Mar 19 and set transplants outside around May 7 – May 21, one to three weeks after the median last frost.

How much rain and snow does 03810 get?

About 45.6 inches of precipitation a year and 62 inches of snowfall (NOAA 1991–2020 normals, Lakeport 2 station).

How hot do summers get in Alton Bay, NH?

The average high peaks at 82 °F in July, with about 9 days a year at 90 °F or more.

What kind of soil does 03810 have?

The USDA soil survey maps Lyman at the center of ZIP 03810: moderately decomposed plant material, somewhat excessively drained, pH about 3.5 (strongly acidic).

Did spring come early in Alton Bay, NH in 2026?

Spring leaf-out near 03810 came on Apr 16 in 2026, 5 days earlier than the 1991–2020 average (Apr 21), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Alton Bay, NH?

Long-day onions: the longest day near 03810 is 15 h 26 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 03810 change?

Yes. The 2012 USDA map put 03810 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.