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

Planting zone for 03285 — Thornton, NH

ZIP code 03285 (Thornton, Grafton County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 15 and the first fall frost September 28.

Where ZIP 03285 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.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostMay 15
First frostSep 28
2012 zone5a

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 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Thornton, 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 Thornton, NH

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 15median — 50% chance of a later frost
Safe for tender plantsMay 29only 10% chance of frost after
First fall frostSeptember 28median — 10% chance by Sep 13
Growing season134 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 2 and returns around October 9.

From the NOAA station Waterville Valley Nepp, NH — 6 miles away, elevation 1,431 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 03285

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 3 – Apr 17
SpinachSow outdoors · Apr 3 – Apr 24
Broccoli, cabbageStart indoors · Mar 6 – Mar 20
Broccoli, cabbageTransplant · Apr 24 – May 8
Onion setsPlant outdoors · Apr 17 – May 1
PotatoesPlant outdoors · Apr 24 – May 8
LettuceSow outdoors · Apr 17 – May 1
Carrots, beetsSow outdoors · Apr 24 – May 8
TomatoesStart indoors · Mar 20 – Apr 3
TomatoesTransplant · May 22 – Jun 5
Peppers, eggplantStart indoors · Mar 6 – Mar 20
Peppers, eggplantTransplant · May 29 – Jun 12
BeansSow outdoors · May 22 – Jun 5
Sweet cornSow outdoors · May 22 – Jun 5
Cucumbers, squashSow outdoors · May 22 – Jun 5
Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17
GarlicPlant cloves · Sep 14 – Oct 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 15) and first fall frost (Sep 28) 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 03285 came on Apr 16 — 10 days earlier than the 1991–2020 average (Apr 26).

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 5a in New Hampshire

467 plants native to the lower 48 states, recorded in New Hampshire, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 52

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 93

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 165

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 140

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 Thornton, NH.

Soil in Thornton, NH

The center of ZIP 03285 is mapped as No Digital Data Available: 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 03285; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Thornton, NH

Summer high77 °Faverage high, July
Winter low6 °Faverage low, January
Hot days1days a year at 90 °F or more
Freezing nights188nights a year at 32 °F or less
Growing degree days1,634base 50 °F — the season’s usable heat
Longest day15 h 29 mindaylight on June 21
Shortest day8 h 53 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation53.8 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 28 °F, low 6 °F 28°6° JanFebruary: average high 30 °F, low 6 °F 30°6° FebMarch: average high 38 °F, low 15 °F 38°15° MarApril: average high 50 °F, low 29 °F 50°29° AprMay: average high 63 °F, low 40 °F 63°40° MayJune: average high 72 °F, low 49 °F 72°49° JunJuly: average high 77 °F, low 54 °F 77°54° JulAugust: average high 76 °F, low 52 °F 76°52° AugSeptember: average high 69 °F, low 45 °F 69°45° SepOctober: average high 56 °F, low 34 °F 56°34° OctNovember: average high 43 °F, low 25 °F 43°25° NovDecember: average high 33 °F, low 14 °F 33°14° Dec

Precipitation by month inches

0″1″2″3″4″5″6″January: 3.91 in precipitation 3.9 JanFebruary: 3.25 in precipitation 3.3 FebMarch: 4.30 in precipitation 4.3 MarApril: 4.64 in precipitation 4.6 AprMay: 4.16 in precipitation 4.2 MayJune: 5.16 in precipitation 5.2 JunJuly: 4.79 in precipitation 4.8 JulAugust: 4.35 in precipitation 4.3 AugSeptember: 4.18 in precipitation 4.2 SepOctober: 5.62 in precipitation 5.6 OctNovember: 4.48 in precipitation 4.5 NovDecember: 4.98 in precipitation 5.0 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Waterville Valley Nepp, NH (6 mi away); precipitation: Waterville Valley Nepp, NH (6 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.

032935b
Woodstock, NH · 3 mi
032625a
North Woodstock, NH · 5 mi
032235a
Campton, NH · 7 mi
032595a
North Sandwich, NH · 8 mi
032515a
Lincoln, NH · 10 mi
032795a
Warren, NH · 11 mi
037855a
Woodsville, NH · 12 mi
032275b
Center Sandwich, NH · 13 mi

New Hampshire planting zones →

Questions about 03285

What planting zone is ZIP code 03285?

ZIP code 03285 (Thornton, NH) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Thornton, NH?

The median last spring frost (32 °F) near 03285 is May 15; after May 29 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Waterville Valley Nepp station.

When is the first frost in Thornton, NH?

The median first fall frost near 03285 is September 28, giving a median frost-free growing season of 134 days.

When should I plant tomatoes in 03285?

Start tomato seeds indoors around Mar 20 – Apr 3 and set transplants outside around May 22 – Jun 5, one to three weeks after the median last frost.

How much rain and snow does 03285 get?

About 53.8 inches of precipitation a year (NOAA 1991–2020 normals, Waterville Valley Nepp station).

How hot do summers get in Thornton, NH?

The average high peaks at 77 °F in July, with about 1 days a year at 90 °F or more.

Did spring come early in Thornton, NH in 2026?

Spring leaf-out near 03285 came on Apr 16 in 2026, 10 days earlier than the 1991–2020 average (Apr 26), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Thornton, NH?

Long-day onions: the longest day near 03285 is 15 h 29 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).