Merrimack County, in New Hampshire, sits in USDA hardiness zone 5b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Merrimack County lies within the Merrimack Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Merrimack County holds more than one microclimate.
Soils and elevations shift across Merrimack 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 Merrimack County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Merrimack County — the short answer
Merrimack County, New Hampshire: USDA zone 5b, about 173 days between hard freezes, across 597K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 26
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 16
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~173
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 597K 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 5b is Merrimack County's average, not your lot's — a low corner or a tree line moves it. Against Merrimack County's 173-day season, see what your own ground reads.
Heat in Merrimack County
Across a year, Merrimack County accumulates about 2,167 growing degree days above 50°F, about 137 more than the middle New Hampshire county — ahead of 7 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 Merrimack County
Across Merrimack County, the ground is predominantly Inceptisols, where Tunbridge, Lyman, and Becket are the most extensive named soil series. The soil is generally well drained with a fine sandy loam surface. Topsoil pH runs about 4.5–4.9, very strongly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
3%
Hydric soils
16%
Soil still varies lot by lot — soil types explained.
How the ground varies across Merrimack County
The USDA soil survey maps 49% of Merrimack County as well drained — but another 48% drains differently: 19% moderately well drained, 8% poorly drained.
Tunbridge is the most extensive named soil at 8% of mapped acres, then Lyman (7%) and Becket (7%).
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 Merrimack County
Each reading below is measured for Merrimack 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 Merrimack County are well drained, in hydrologic group C — 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 Merrimack County runs about pH 4.5–4.9, 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
Wet ground
MeasuredAbout 16% of Merrimack County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredMerrimack County runs about 173 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
The kind of country Merrimack County is in
Merrimack County spans 2 EPA Level III ecoregions — Northeastern Highlands (65%) and Northeastern Coastal Zone (36%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Merrimack County
We scored all 1,086 plants against Merrimack County's own USDA zone 5b and its own 173-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 Merrimack County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 29; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 26 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 16 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
Documented around Merrimack County
Spotted lanternfly documented 27 miles from Merrimack County, first recorded 2022. What to watch for.
- Japanese beetle13 documented records
- monarch butterfly154 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Merrimack County
USGS estimates 2,234 lb of Glyphosate on Merrimack County farmland in 2019, its largest by weight, ahead of Atrazine (1,818 lb) and Metolachlor & Metolachlor-s (1,384 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 Merrimack County — and how to grow with it.
We checked the federal record across Merrimack County — 1,448 documented sites across 7 of the 9 source types we track.
The most significant on record: 2 Superfund sites (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 Merrimack 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 Merrimack County
Closest first, across Merrimack County. Listing isn't leaking, and distance isn't exposure.
- THOMAS GALLAGHERUnderground Storage Tanks · 0.8 mi
- PENACOOK BOSCAWEN WATER PCTPFAS · 1.1 mi
- JAMES HEWEYUnderground Storage Tanks · 1.7 mi
- FORMER SILVER FARMUnderground Storage Tanks · 1.7 mi
- NH-WHW 29Nitrate · 1.8 mi
- CORSER HILL STOREUnderground Storage Tanks · 1.8 mi
- WEBSTER FIRE DEPTUnderground Storage Tanks · 1.8 mi
- BETH ROYUnderground Storage Tanks · 2.0 mi
- NH-WHW 51Nitrate · 2.2 mi
- NH-WHW 17Nitrate · 2.3 mi
- NH-BTW 34Nitrate · 2.3 mi
- NH-WHW 49Nitrate · 2.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Merrimack 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 Merrimack County.
Total Sites
1,448
across Merrimack County
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
across Merrimack County
Severity Distribution
across Merrimack County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Merrimack County, Nitrate runs higher than the national average — 528 sites across Merrimack County. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
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 Merrimack 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 Merrimack County average
Your land is one point inside Merrimack County
Everything above resolves to Merrimack County as a whole — one PHZM band and one county frost record, read across 597K 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 Merrimack County Average
Merrimack County Average
- ●USDA Zones 5b, averaged across Merrimack County
- ●One soil character for all of Merrimack County
- ●Frost dates read at Merrimack County's scale: Apr 26 to Oct 16
YOUR Parcel
- ✓Your exact zone, not Merrimack County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Merrimack County
Pull a site-specific report for your exact address in Merrimack County, New Hampshire — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Merrimack County averages can't show:
We read public map data around Merrimack County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Merrimack County average
How we know this about Merrimack 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 Merrimack County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Merrimack County
When does frost risk typically end in Merrimack County?
The last hard freeze (28°F) in Merrimack County typically lands around Apr 26, 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 17.
How long is the growing season in Merrimack County?
Measured between 28°F hard freezes, Merrimack County sees about 173 frost-free days — roughly Apr 26 through Oct 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 17 to Oct 2, about 138 days.
Is the soil safe to grow vegetables in Merrimack County?
The federal record around Merrimack County is a meaningful one — 1,448 documented sites, mostly Underground Storage Tanks entries (559), the nearest Underground Storage Tanks record about 0.8 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 Merrimack County's scale — its 5b band and its 173-day season. Your yard writes its own version of Merrimack 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 Merrimack County’s own scale
9 of the readings below were taken at Merrimack County's own scale — its own ~173-day span between 28°F freezes, the 3 most extensive soil series mapped here and 1,448 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Merrimack County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Merrimack County's own 28°F hard-freeze dates and its ~173-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Merrimack CountyUSDA NRCS SSURGO
- 1,448 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.8 miles outFederal environmental registers
- Merrimack County's boundary and the 597,024 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~173-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Merrimack County spans, Northeastern Highlands the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Merrimack County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Merrimack 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 Merrimack County — the ~173 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 Merrimack County's 597,024 acreswhy one lot differs from the next →
- Which of those 1,448 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 Merrimack Countyread your own land →