Sullivan County, in New Hampshire, sits in USDA hardiness zone 5a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Reliable performers under these conditions include cabbage, cranberry, lavender, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Sullivan County holds more than one microclimate.
Soils and elevations shift across Sullivan County, so your frost dates and drainage aren't the county average. 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 Sullivan County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Sullivan County — the short answer
Sullivan County, New Hampshire: USDA zone 5a, about 159 days between hard freezes, across 344K acres.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 3
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 9
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~159
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 344K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 5a is Sullivan County's average, not your lot's — a low corner or a tree line moves it. Against Sullivan County's 159-day season, see what your own ground reads.
Heat in Sullivan County
Across a year, Sullivan County accumulates about 1,940 growing degree days above 50°F, about 90 fewer than the middle New Hampshire county — ahead of 4 of New Hampshire’s 10 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Sullivan County
Across Sullivan County, the ground is predominantly Spodosols, where Monadnock, Marlow, and Lyman are the most extensive named soil series. The soil is generally well drained with a fine sandy loam surface. Topsoil pH runs about 4.3–5.3, very strongly acidic. Rainfall drains through hydrologic group B soils.
Soil order
Spodosols
Drainage
Well drained
Prime farmland
5%
Hydric soils
10%
Soil still varies lot by lot — soil types explained.
How the ground varies across Sullivan County
The USDA soil survey maps 62% of Sullivan County as well drained — but another 35% drains differently: 11% somewhat excessively drained, 11% moderately well drained.
Monadnock is the most extensive named soil at 25% of mapped acres, then Marlow (15%) and Lyman (9%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Sullivan County
Each reading below is measured for Sullivan County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Sullivan County are well drained, in hydrologic group B — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Sullivan County runs about pH 4.3–5.3, on the acidic side.
Blueberries, potatoes, and rhododendrons thrive in it, but most vegetables start locking out nutrients below about pH 6.0 and grow pale and stunted no matter how much you feed them.
A measured lime application raises pH for the crops that need it — but test first, because the right rate depends on your own soil, not the county average.
USDA NRCS SSURGO
Season length
MeasuredSullivan County runs about 159 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
MeasuredSullivan County sits in USDA hardiness zone 5a.
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 Sullivan County is in
Sullivan County sits in the Northeastern Highlands — EPA Level III, inside the wider Northern Forests. One consistent ecological setting across the whole county.
What Grows in Sullivan County
We scored all 1,086 plants against Sullivan County's own USDA zone 5a and its own 159-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's New Hampshire profile.
Is it too late to plant in Sullivan County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Apr 5; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 3 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 9 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
Documented around Sullivan County
Spotted lanternfly documented 12 miles from Sullivan County, first recorded 2023. What to watch for.
- Japanese beetle33 documented records
- monarch butterfly143 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Sullivan County
USGS estimates 2,043 lb of Glyphosate on Sullivan County farmland in 2019, its largest by weight, ahead of Atrazine (1,654 lb) and Metolachlor & Metolachlor-s (1,295 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Sullivan County — and how to grow with it.
We checked the federal record across Sullivan County — 370 documented sites across 8 of the 9 source types we track.
The most significant on record: 1 Superfund site (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Sullivan County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Sullivan County
Closest first, across Sullivan County. Listing isn't leaking, and distance isn't exposure.
- TOM AND DALES AUTO BODY REPAIRBrownfields · 0.7 mi
- SPANOS CHRIS AUTOBrownfields · 0.9 mi
- NH DOTUnderground Storage Tanks · 1.1 mi
- NEWPORT WATER WORKSPFAS · 1.2 mi
- NEWPORT CHEVROLET BUICK GMCBrownfields · 1.2 mi
- FLEURYSBrownfields · 1.2 mi
- LATVA MACHINE INCORPORATEDToxics Release Inventory · 1.4 mi
- CASELLA WASTE MGMT INCBrownfields · 1.4 mi
- GDS TRANSFER STATION NEWPORTUnderground Storage Tanks · 1.5 mi
- KATHAN GARDENSUnderground Storage Tanks · 1.9 mi
- WOODLAWN NURSING HOMEUnderground Storage Tanks · 2.0 mi
- WEARE MOBILUnderground Storage Tanks · 2.1 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Sullivan County'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 Sullivan County.
Total Sites
370
across Sullivan County
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Severity Distribution
across Sullivan County
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •Near a brownfield, raised beds of imported soil give your food clean ground.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
Check your specific parcel in Sullivan County
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 Sullivan County average
Your land is one point inside Sullivan County
Everything above resolves to Sullivan County as a whole — one PHZM band and one county frost record, read across 344K 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 county 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 county average.
Your Lot vs the Sullivan County Average
Sullivan County Average
- ●USDA Zones 5a, averaged across Sullivan County
- ●One soil character for all of Sullivan County
- ●Frost dates read at Sullivan County's scale: May 3 to Oct 9
YOUR Parcel
- ✓Your exact zone, not Sullivan County's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Sullivan County
Pull a site-specific report for your exact address in Sullivan County, New Hampshire — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Sullivan County averages can't show:
We read public map data around Sullivan County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Sullivan County average
How we know this about Sullivan County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Sullivan County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Sullivan County
When does frost risk typically end in Sullivan County?
The last hard freeze (28°F) in Sullivan County typically lands around May 3, 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 24.
How long is the growing season in Sullivan County?
Measured between 28°F hard freezes, Sullivan County sees about 159 frost-free days — roughly May 3 through Oct 9, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 24 to Sep 25, about 124 days.
Is the soil safe to grow vegetables in Sullivan County?
The federal record around Sullivan County is a meaningful one — 370 documented sites, mostly Underground Storage Tanks entries (202), the nearest Brownfields record about 0.7 miles 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.
Everything above is measured at Sullivan County's scale — its 5a band and its 159-day season. Your yard writes its own version of Sullivan County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads New Hampshire's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Sullivan County’s own scale
9 of the readings below were taken at Sullivan County's own scale — its own ~159-day span between 28°F freezes, the 3 most extensive soil series mapped here and 370 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Sullivan County's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Sullivan County's own 28°F hard-freeze dates and its ~159-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Sullivan CountyUSDA NRCS SSURGO
- 370 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 0.7 miles outFederal environmental registers
- Sullivan County's boundary and the 344,244 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~159-day seasonGrowable Ground crop-matching engine
- Sullivan County sitting wholly inside the Northeastern HighlandsUS EPA Level III Ecoregions
- Open occurrence records documented in Sullivan County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Sullivan County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every New Hampshire grower plans around — written at state scale, so they stay on the state guidefrom New Hampshire
What this page can’t tell you
- How the season shifts across Sullivan County — the ~159 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Sullivan County's 344,244 acreswhy one lot differs from the next →
- Which of those 370 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Sullivan Countyread your own land →