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

Planting zone for 03603 — Charlestown, NH

ZIP code 03603 (Charlestown, Sullivan County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 9 and the first fall frost October 2.

Where ZIP 03603 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 frostMay 9

First frostOct 2

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 Charlestown, 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 Charlestown, NH

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 9median — 50% chance of a later frost

Safe for tender plantsMay 22only 10% chance of frost after

First fall frostOctober 2median — 10% chance by Sep 21

Growing season146 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 27 and returns around October 14.

From the NOAA station N Springfield Lake, VT — 9 miles away, elevation 561 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 03603

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 28 – Apr 11

SpinachSow outdoors · Mar 28 – Apr 18

Broccoli, cabbageStart indoors · Feb 28 – Mar 14

Broccoli, cabbageTransplant · Apr 18 – May 2

Onion setsPlant outdoors · Apr 11 – Apr 25

PotatoesPlant outdoors · Apr 18 – May 2

LettuceSow outdoors · Apr 11 – Apr 25

Carrots, beetsSow outdoors · Apr 18 – May 2

TomatoesStart indoors · Mar 14 – Mar 28

TomatoesTransplant · May 16 – May 30

Peppers, eggplantStart indoors · Feb 28 – Mar 14

Peppers, eggplantTransplant · May 23 – Jun 6

BeansSow outdoors · May 16 – May 30

Sweet cornSow outdoors · May 16 – May 30

Cucumbers, squashSow outdoors · May 16 – May 30

Fall lettuce, spinachSow outdoors · Aug 7 – Aug 21

GarlicPlant cloves · Sep 18 – Oct 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Oct 2) 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 03603 came on Apr 12 — 7 days earlier than the 1991–2020 average (Apr 19).

average
Apr 192026
Apr 12

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.

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 Charlestown, NH.

Soil in Charlestown, NH

The soil mapped at the center of ZIP 03603 is Saco variant — mucky silt loam, very poorly drained.

TextureMucky silt loama good balance for most vegetables

pH5.8moderately acidic; most vegetables like 6.0–7.0

DrainageVery poorly drainedconsider raised beds

Organic matter8%high

Hydrologic groupB/Dmoderate when drained; wet otherwise

Farmland classNot prime farmlandUSDA classification

Map unit: Saco variant mucky silt loam.

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 03603; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Charlestown, NH

Summer high83 °Faverage high, July

Winter low9 °Faverage low, January

Hot days11days a year at 90 °F or more

Freezing nights173nights a year at 32 °F or less

Growing degree days2,243base 50 °F — the season’s usable heat

Longest day15 h 24 mindaylight on June 21

Shortest day8 h 58 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation42 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: N Springfield Lake, VT (9 mi away); precipitation: West Unity 0.7 Wsw, NH (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

036016a

Acworth, NH · 3 mi

051565b

Springfield, VT · 6 mi

036075b

South Acworth, NH · 7 mi

036026a

Alstead, NH · 8 mi

036045b

Drewsville, NH · 8 mi

036095b

North Walpole, NH · 8 mi

037435b

Claremont, NH · 8 mi

051015b

Bellows Falls, VT · 8 mi

New Hampshire planting zones →

Questions about 03603

What planting zone is ZIP code 03603?

ZIP code 03603 (Charlestown, 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 Charlestown, NH?

The median last spring frost (32 °F) near 03603 is May 9; after May 22 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, N Springfield Lake station.

When is the first frost in Charlestown, NH?

The median first fall frost near 03603 is October 2, giving a median frost-free growing season of 146 days.

When should I plant tomatoes in 03603?

Start tomato seeds indoors around Mar 14 – Mar 28 and set transplants outside around May 16 – May 30, one to three weeks after the median last frost.

How much rain and snow does 03603 get?

About 42 inches of precipitation a year (NOAA 1991–2020 normals, West Unity 0.7 Wsw station).

How hot do summers get in Charlestown, NH?

The average high peaks at 83 °F in July, with about 11 days a year at 90 °F or more.

What kind of soil does 03603 have?

The USDA soil survey maps Saco variant at the center of ZIP 03603: mucky silt loam, very poorly drained, pH about 5.8 (moderately acidic).

Did spring come early in Charlestown, NH in 2026?

Spring leaf-out near 03603 came on Apr 12 in 2026, 7 days earlier than the 1991–2020 average (Apr 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Charlestown, NH?

Long-day onions: the longest day near 03603 is 15 h 24 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 03603 change?

Yes. The 2012 USDA map put 03603 in zone 5a; the 2023 map puts it in zone 5b. The newer map uses 1991–2020 data and more weather stations.