Boundary 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.
Reliable performers under these conditions include cabbage, blackberry, california poppy, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Boundary County lies within the Idaho Panhandle (North Idaho) — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Boundary County holds more than one microclimate.
Soils and elevations shift across Boundary 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 Boundary County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Boundary County — the short answer
Boundary County, Idaho: USDA zone 6a, about 148 days between hard freezes, across 812K acres.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 12
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 7
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~148
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 812K 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 Boundary County's average, not your lot's — a low corner or a tree line moves it. Against Boundary County's 148-day season, see what your own ground reads.
Heat in Boundary County
Across a year, Boundary County accumulates about 603 growing degree days above 50°F, about 888 fewer than the middle Idaho county — ahead of 1 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 Boundary County
Across Boundary County, the ground is predominantly Inceptisols, where Pend Oreille, Rubson, and Idamont are the most extensive named soil series. The soil is generally well drained with a ashy silt loam surface. Topsoil pH runs about 5.8–6.6, slightly acidic. Rainfall drains through hydrologic group B soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
5%
Hydric soils
4%
Soil still varies lot by lot — soil types explained.
How the ground varies across Boundary County
The USDA soil survey maps 59% of Boundary County as well drained — but another 33% drains differently: 25% moderately well drained, 4% poorly drained.
Pend Oreille is the most extensive named soil at 5% of mapped acres, then Rubson (3%) and Idamont (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 Boundary County
Each reading below is measured for Boundary 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 Boundary 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 Boundary County runs about pH 5.8–6.6, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredBoundary County runs about 148 days between hard freezes — a short growing season.
Long-maturing crops like melons, sweet potatoes, and winter squash can run out of runway before the first hard freeze, ripening late or not at all.
Lead with fast-maturing varieties, and stretch the season on both ends with cold frames, low tunnels, or a greenhouse.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredBoundary 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 Boundary County is in
Boundary County sits in the Northern Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. One consistent ecological setting across the whole county.
What Grows in Boundary County
We scored all 1,086 plants against Boundary County's own USDA zone 6a and its own 148-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 Boundary County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 14; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 12 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 7 — long-season crops need about 90 days of runway, quick greens only 30. In a season this compact, fast finishers and cold-hardy greens do the late work, and garlic tucked in before the freeze repays you next summer.
What gets applied to farmland in Boundary County
USGS estimates 9,220 lb of Glyphosate on Boundary County farmland in 2019, its largest by weight, ahead of Bromoxynil (3,447 lb) and Metribuzin (2,212 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 Boundary County — and how to grow with it.
We checked the federal record across Boundary County — 185 documented sites across 6 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.
Boundary County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Boundary County
Closest first, across Boundary County. Listing isn't leaking, and distance isn't exposure.
- Name UnknownMining · 1.8 mi
- 63N 01W 24CAB1Nitrate · 5.4 mi
- 62N 01E 07BCD1Nitrate · 6.4 mi
- 62N 01W 24CAB1Nitrate · 6.6 mi
- 64N 01W 35DBA1Nitrate · 7.2 mi
- ELK MOUNTAIN FARMS BACKWOODSBrownfields · 7.2 mi
- 62N 01E 20CBA1-DESTROYEDNitrate · 8.3 mi
- 61N 01E 06AAB1Nitrate · 9.5 mi
- 64N 01W 08AAB1Nitrate · 10.2 mi
- AMBUSH ROCK LANDFILLSuperfund · 10.3 mi
- WI FOREST PRODUCTSUnderground Storage Tanks · 10.3 mi
- CROWN PACIFIC MILL SITEToxics Release Inventory · 10.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Boundary 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 Boundary County.
Total Sites
185
across Boundary County
Risk Level
High
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
across Boundary County
Severity Distribution
across Boundary County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Boundary County, two things run higher than the national average across Boundary County — Mining (60 sites) and Nitrate (54 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Boundary 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 Boundary County average
Your land is one point inside Boundary County
Everything above resolves to Boundary County as a whole — one PHZM band and one county frost record, read across 812K 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 Boundary County Average
Boundary County Average
- ●USDA Zones 6a, averaged across Boundary County
- ●One soil character for all of Boundary County
- ●Frost dates read at Boundary County's scale: May 12 to Oct 7
YOUR Parcel
- ✓Your exact zone, not Boundary County's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Boundary County
Pull a site-specific report for your exact address in Boundary County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Boundary County averages can't show:
We read public map data around Boundary County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Boundary County average
How we know this about Boundary 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 Boundary County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Boundary County
When does frost risk typically end in Boundary County?
The last hard freeze (28°F) in Boundary County typically lands around May 12, 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 Jun 2.
How long is the growing season in Boundary County?
Measured between 28°F hard freezes, Boundary County sees about 148 frost-free days — roughly May 12 through Oct 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 2 to Sep 23, about 113 days.
Is the soil safe to grow vegetables in Boundary County?
The federal record around Boundary County runs heavier than most — 185 documented sites, mostly Underground Storage Tanks entries (61), the nearest Mining record about 1.8 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
How do gardeners stretch the season in Boundary County?
With about 148 frost-free days between hard freezes, Boundary County rewards the classic extension moves: floating row cover buys roughly two to four extra weeks at each shoulder — on this season that is a working window nearer 176 to 204 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 12 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Boundary County's scale — its 6a band and its 148-day season. Your yard writes its own version of Boundary 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 Boundary County’s own scale
8 of the readings below were taken at Boundary County's own scale — its own ~148-day span between 28°F freezes, the 3 most extensive soil series mapped here and 185 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Boundary County's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Boundary County's own 28°F hard-freeze dates and its ~148-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Boundary CountyUSDA NRCS SSURGO
- 185 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 1.8 miles outFederal environmental registers
- Boundary County's boundary and the 811,954 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~148-day seasonGrowable Ground crop-matching engine
- Boundary County sitting wholly inside the Northern RockiesUS EPA Level III Ecoregions
- Which agricultural compounds go onto Boundary 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 Boundary County — the ~148 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 Boundary County's 811,954 acreswhy one lot differs from the next →
- Which of those 185 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 Boundary Countyread your own land →