Alton, New Hampshire, sits in USDA hardiness zone 5b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Well-matched crops include cabbage, cranberry, lavender, and collard greens, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Even in Alton, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Alton lot. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Alton — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Alton — the short answer
Alton, New Hampshire: USDA zone 5b, about 188 days between hard freezes, across 300 acres of town.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 19
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 24
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~188
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 300 acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 5b is Alton's average, not your lot's — a low corner or a tree line moves it. Against Alton's 188-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Alton
Each reading below is measured for Alton itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredAlton runs about 188 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredAlton sits in USDA hardiness zone 5b.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Alton is in
Alton sits in the Northeastern Highlands — EPA Level III, inside the wider Northern Forests. That is read at Alton's own centroid rather than borrowed from Belknap County.
What Grows in Alton
Every plant below cleared Alton's own zone 5b and its 188-day season. Each card opens that plant's New Hampshire profile. How we score.
Is it too late to plant in Alton?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 22; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 19 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 24 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
Documented around Alton
Spotted lanternfly documented 21 miles from Alton, first recorded 2022. What to watch for.
What's on the federal record near Alton
Closest first, within ~10 miles of Alton. Listing isn't leaking, and distance isn't exposure.
- ALTON VILLAGE STORE & GASUnderground Storage Tanks · 500 ft
- SHIELDS BEST VALUE GASUnderground Storage Tanks · 1000 ft
- ALTON HIGHWAY GARAGEUnderground Storage Tanks · 1600 ft
- RYAN BUILDINGUnderground Storage Tanks · 1600 ft
- SANDY POINT BEACH RESORT INCUnderground Storage Tanks · 1700 ft
- PARKER MARINE, INC.Underground Storage Tanks · 1700 ft
- ALTON HOME CENTERUnderground Storage Tanks · 1700 ft
- NH-AHW 64Nitrate · 1900 ft
- ALTON HIGHWAY GARAGEBrownfields · 2100 ft
- ALTON DISTRICT OFFICEUnderground Storage Tanks · 2100 ft
- FORMER MOUNT MAJOR COUNTRY STOREUnderground Storage Tanks · 2400 ft
- ALTON CIRCLE MARKETUnderground Storage Tanks · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Alton's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Alton.
Total Sites
251
within ~10 miles of Alton
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Alton
Severity Distribution
within ~10 miles of Alton
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Alton, Nitrate runs higher than the national average — 106 sites within ~10 miles of Alton. That's not a problem with your land — it's information about it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Alton
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Alton average
Your land is one point inside Alton
Everything above resolves to Alton as a whole — one PHZM band and one 28°F frost record, read across 300 acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at town scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better local average.
Your Lot vs the Alton Average
Alton Average
- ●USDA Zones 5b, averaged across Alton
- ●One soil character for all of Alton
- ●Frost dates read at Alton's scale: Apr 19 to Oct 24
YOUR Parcel
- ✓Your exact zone, not Alton's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Alton
Pull a site-specific report for your exact address in Alton, New Hampshire — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Alton averages can't show:
We read public map data around Alton — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Alton average
How we know this about Alton
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Alton’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at town grain anywhere on this page — there is no town-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Alton
When does frost risk typically end in Alton?
The last hard freeze (28°F) in Alton typically lands around Apr 19, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about May 10.
When is the first frost in Alton?
The first hard freeze (28°F) in Alton typically arrives around Oct 24, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 10, so the watching starts about Sep 24 — about 188 days after the spring freeze cleared.
How long is the growing season in Alton?
Measured between 28°F hard freezes, Alton sees about 188 frost-free days — roughly Apr 19 through Oct 24, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 10 to Oct 10, about 153 days.
Is the soil safe to grow vegetables in Alton?
The federal record around Alton is a meaningful one — 251 documented sites, mostly Underground Storage Tanks entries (122), the nearest Underground Storage Tanks record under a tenth of a mile out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Alton?
From about Sep 24 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 24 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 24. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Alton's scale — its 5b band and its 188-day season. Your yard writes its own version of Alton's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Alton’s own scale
7 of the readings below were taken at Alton's own scale — its own ~188-day season between 28°F freezes, the 300 acres it covers and 251 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Alton's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Alton's own 28°F hard-freeze dates, about Apr 19 and Oct 24 and the ~188-day span between themNOAA 1991–2020 Climate Normals
- 251 documented contamination sites on the federal record near Alton, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Alton's boundary and the 300 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~188-day seasonGrowable Ground crop-matching engine
- The ecoregion at Alton's own centroid, the Northeastern HighlandsUS EPA Level III Ecoregions
- A documented spotted-lanternfly record within reach of Altonlydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- Soil character — no town-scale survey exists, so Alton's 300 acres read through its county's SSURGO summaryfrom Belknap County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Belknap County
- The growing challenges every New Hampshire grower plans around — written at state scale, so they stay on the state guidefrom New Hampshire
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Belknap County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Alton's 300 acreswhy one lot differs from the next →
- Which side of Alton you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 300 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record under a tenth of a mile out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Alton-wide figureread your own land →
More in New Hampshire
Growing region
Nearby growing guides