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

Planting zone for 03820 — Dover, NH

ZIP code 03820 (Dover, Strafford County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 3 and the first fall frost October 10.

Where ZIP 03820 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.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 3
First frostOct 10
2012 zone5b

Was 5b 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 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Dover, 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 Dover, NH

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 3median — 50% chance of a later frost
Safe for tender plantsMay 16only 10% chance of frost after
First fall frostOctober 10median — 10% chance by Sep 27
Growing season158 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 23.

From the NOAA station Durham 2 N, NH — 2 miles away, elevation 118 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 03820

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 22 – Apr 5
SpinachSow outdoors · Mar 22 – Apr 12
Broccoli, cabbageStart indoors · Feb 22 – Mar 8
Broccoli, cabbageTransplant · Apr 12 – Apr 26
Onion setsPlant outdoors · Apr 5 – Apr 19
PotatoesPlant outdoors · Apr 12 – Apr 26
LettuceSow outdoors · Apr 5 – Apr 19
Carrots, beetsSow outdoors · Apr 12 – Apr 26
TomatoesStart indoors · Mar 8 – Mar 22
TomatoesTransplant · May 10 – May 24
Peppers, eggplantStart indoors · Feb 22 – Mar 8
Peppers, eggplantTransplant · May 17 – May 31
BeansSow outdoors · May 10 – May 24
Sweet cornSow outdoors · May 10 – May 24
Cucumbers, squashSow outdoors · May 10 – May 24
Fall lettuce, spinachSow outdoors · Aug 15 – Aug 29
GarlicPlant cloves · Sep 26 – Oct 31
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 3) and first fall frost (Oct 10) 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 03820 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 Dover, NH.

Soil in Dover, NH

The center of ZIP 03820 is mapped as Made land: built-over ground without natural soil data. Garden soil here is usually imported or disturbed — test before you plant.

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 03820; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Dover, NH

Summer high81 °Faverage high, July
Winter low15 °Faverage low, January
Hot days6days a year at 90 °F or more
Freezing nights150nights a year at 32 °F or less
Growing degree days2,266base 50 °F — the season’s usable heat
Longest day15 h 23 mindaylight on June 21
Shortest day8 h 59 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation47.8 inper year, rain and melted snow

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 32 °F, low 15 °F 32°15° JanFebruary: average high 36 °F, low 16 °F 36°16° FebMarch: average high 43 °F, low 25 °F 43°25° MarApril: average high 55 °F, low 34 °F 55°34° AprMay: average high 66 °F, low 44 °F 66°44° MayJune: average high 75 °F, low 53 °F 75°53° JunJuly: average high 81 °F, low 59 °F 81°59° JulAugust: average high 80 °F, low 57 °F 80°57° AugSeptember: average high 72 °F, low 50 °F 72°50° SepOctober: average high 60 °F, low 39 °F 60°39° OctNovember: average high 48 °F, low 30 °F 48°30° NovDecember: average high 38 °F, low 22 °F 38°22° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.38 in precipitation 3.4 JanFebruary: 3.52 in precipitation 3.5 FebMarch: 4.39 in precipitation 4.4 MarApril: 4.20 in precipitation 4.2 AprMay: 3.80 in precipitation 3.8 MayJune: 4.28 in precipitation 4.3 JunJuly: 3.76 in precipitation 3.8 JulAugust: 3.43 in precipitation 3.4 AugSeptember: 3.86 in precipitation 3.9 SepOctober: 4.79 in precipitation 4.8 OctNovember: 3.95 in precipitation 4.0 NovDecember: 4.47 in precipitation 4.5 Dec

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

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6a.

038216a
Dover, NH · <1 mi
038226a
Dover, NH · <1 mi
038236a
Madbury, NH · 3 mi
038696a
Rollinsford, NH · 3 mi
038786a
Somersworth, NH · 5 mi
038246a
Durham, NH · 5 mi
039036a
Eliot, ME · 6 mi
039086a
South Berwick, ME · 7 mi

All 3 ZIP codes in Dover → · New Hampshire planting zones →

Questions about 03820

What planting zone is ZIP code 03820?

ZIP code 03820 (Dover, 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 Dover, NH?

The median last spring frost (32 °F) near 03820 is May 3; after May 16 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Durham 2 N station.

When is the first frost in Dover, NH?

The median first fall frost near 03820 is October 10, giving a median frost-free growing season of 158 days.

When should I plant tomatoes in 03820?

Start tomato seeds indoors around Mar 8 – Mar 22 and set transplants outside around May 10 – May 24, one to three weeks after the median last frost.

How much rain and snow does 03820 get?

About 47.8 inches of precipitation a year (NOAA 1991–2020 normals, Durham 2 N station).

How hot do summers get in Dover, NH?

The average high peaks at 81 °F in July, with about 6 days a year at 90 °F or more.

Did spring come early in Dover, NH in 2026?

Spring leaf-out near 03820 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 Dover, NH?

Long-day onions: the longest day near 03820 is 15 h 23 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 03820 change?

Yes. The 2012 USDA map put 03820 in zone 5b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.