Franklin County, in Idaho, sits in USDA hardiness zone 6a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
These conditions suit cabbage, blackberry, california poppy, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Franklin County lies within the Cache Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Franklin County holds more than one microclimate.
Soils and elevations shift across Franklin 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 Franklin County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Franklin County — the short answer
Franklin County, Idaho: USDA zone 6a, about 166 days between hard freezes, across 424K acres.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 28
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 11
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~166
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 424K 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 6a is Franklin County's average, not your lot's — a low corner or a tree line moves it. Against Franklin County's 166-day season, see what your own ground reads.
Heat in Franklin County
Across a year, Franklin County accumulates about 2,012 growing degree days above 50°F, about 521 more than the middle Idaho county — ahead of 35 of Idaho’s 44 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 Franklin County
Across Franklin County, the ground is predominantly Mollisols, where Manila, Oxford, and Parleys are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 6.9–7.8, neutral. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
2%
Soil still varies lot by lot — soil types explained.
How the ground varies across Franklin County
The USDA soil survey maps 77% of Franklin County as well drained — but another 22% drains differently: 14% moderately well drained, 5% somewhat poorly drained.
Manila is the most extensive named soil at 4% of mapped acres, then Oxford (4%) and Parleys (3%).
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 Franklin County
Each reading below is measured for Franklin 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 Franklin 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 Franklin County runs about pH 6.9–7.8, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredFranklin County runs about 166 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
MeasuredFranklin County sits in USDA hardiness zone 6a.
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 Franklin County is in
Franklin County spans 3 EPA Level III ecoregions — Northern Basin and Range (37%), Central Basin and Range (35%) and Wasatch and Uinta Mountains (28%). 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 Franklin County
We scored all 1,086 plants against Franklin County's own USDA zone 6a and its own 166-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 Idaho profile.
Is it too late to plant in Franklin 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 Mar 31; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 28 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 11 — 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 Franklin County
- monarch butterfly2 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Franklin County
USGS estimates 25,091 lb of Glyphosate on Franklin County farmland in 2019, its largest by weight, ahead of 2,4-d (8,752 lb) and Metolachlor-s (4,783 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 Franklin County — and how to grow with it.
We checked the federal record across Franklin County — 105 documented sites across 7 of the 9 source types we track.
The most significant on record: 1 Toxics Release Inventory facility. Active industrial facilities reporting chemical releases to air, water, and land.
The federal record across Franklin County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Franklin County
Closest first, across Franklin County. Listing isn't leaking, and distance isn't exposure.
- 14S 40E 29BDD1Nitrate · 0.7 mi
- 14S 39E 25ADD1Nitrate · 0.8 mi
- 14S 40E 21AAC1Nitrate · 2.5 mi
- PRESTON CITY OFPFAS · 3.6 mi
- 15S 39E 09BAB2Nitrate · 5.1 mi
- 15S 39E 09BAB1-DESTROYEDNitrate · 5.1 mi
- 15S 39E 23BBB1Nitrate · 5.1 mi
- Well Come MartUnderground Storage Tanks · 5.1 mi
- BOWEN FORD MERCURYUnderground Storage Tanks · 5.1 mi
- INTERMOUNTAIN FARMERS (4)Underground Storage Tanks · 5.4 mi
- PRESTON SERVICE CENTERUnderground Storage Tanks · 5.5 mi
- WEST MOTOR CO INCUnderground Storage Tanks · 5.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Franklin 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 Franklin County.
Total Sites
105
across Franklin County
Risk Level
Moderate
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
across Franklin County
Severity Distribution
across Franklin County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Franklin County, Nitrate runs higher than the national average — 54 sites across Franklin 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 Franklin 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 Franklin County average
Your land is one point inside Franklin County
Everything above resolves to Franklin County as a whole — one PHZM band and one county frost record, read across 424K 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 Franklin County Average
Franklin County Average
- ●USDA Zones 6a, averaged across Franklin County
- ●One soil character for all of Franklin County
- ●Frost dates read at Franklin County's scale: Apr 28 to Oct 11
YOUR Parcel
- ✓Your exact zone, not Franklin County's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Franklin County
Pull a site-specific report for your exact address in Franklin County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Franklin County averages can't show:
We read public map data around Franklin County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Franklin County average
How we know this about Franklin 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 Franklin County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Franklin County
When does frost risk typically end in Franklin County?
The last hard freeze (28°F) in Franklin County typically lands around Apr 28, 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 19.
How long is the growing season in Franklin County?
Measured between 28°F hard freezes, Franklin County sees about 166 frost-free days — roughly Apr 28 through Oct 11, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 19 to Sep 27, about 131 days.
Is the soil safe to grow vegetables in Franklin County?
The federal record around Franklin County shows 105 documented sites, mostly Nitrate entries (54), the nearest Nitrate record about 0.7 miles out — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Everything above is measured at Franklin County's scale — its 6a band and its 166-day season. Your yard writes its own version of Franklin 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 Idaho's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Franklin County’s own scale
9 of the readings below were taken at Franklin County's own scale — its own ~166-day span between 28°F freezes, the 3 most extensive soil series mapped here and 105 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Franklin County's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Franklin County's own 28°F hard-freeze dates and its ~166-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Franklin CountyUSDA NRCS SSURGO
- 105 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 0.7 miles outFederal environmental registers
- Franklin County's boundary and the 424,332 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~166-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Franklin County spans, Northern Basin and Range the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Franklin County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Franklin County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Idaho grower plans around — written at state scale, so they stay on the state guidefrom Idaho
What this page can’t tell you
- How the season shifts across Franklin County — the ~166 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 Franklin County's 424,332 acreswhy one lot differs from the next →
- Which of those 105 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 Franklin Countyread your own land →