Custer County, in Idaho, sits in USDA hardiness zone 6a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Reliable performers under these conditions include pumpkin, blackberry, california poppy, and zucchini; what your own ground favors still comes down to its soil, sun, and drainage.
Custer County lies within the Central Idaho Mountains — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Custer County holds more than one microclimate.
Soils and elevations shift across Custer 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 Custer County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Custer County — the short answer
Custer County, Idaho: USDA zone 6a, about 104 days between hard freezes, across 3.2M acres.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 3
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 15
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~104
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 3.2M 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 Custer County's average, not your lot's — a low corner or a tree line moves it. Against Custer County's 104-day season, see what your own ground reads.
Heat in Custer County
Across a year, Custer County accumulates about 997 growing degree days above 50°F, about 494 fewer than the middle Idaho county — ahead of 5 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 Custer County
Across Custer County, the ground is predominantly Mollisols, where Dawtonia, Zeebar, and Dacont are the most extensive named soil series. The soil is generally well drained with a gravelly loam surface. Topsoil pH runs about 7.0–7.9, slightly alkaline. Rainfall drains through hydrologic group B soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
4%
Soil still varies lot by lot — soil types explained.
How the ground varies across Custer County
The USDA soil survey maps 80% of Custer County as well drained — but another 19% drains differently: 13% somewhat excessively drained, 3% poorly drained.
Dawtonia is the most extensive named soil at 6% of mapped acres, then Zeebar (5%) and Dacont (4%).
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 Custer County
Each reading below is measured for Custer 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 Custer 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 Custer County runs about pH 7.0–7.9, 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
MeasuredCuster County runs about 104 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
MeasuredCuster 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 Custer County is in
Custer County spans 2 EPA Level III ecoregions — Idaho Batholith (53%) and Middle Rockies (47%). 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 Custer County
We scored all 1,086 plants against Custer County's own USDA zone 6a and its own 104-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 Custer County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around May 6; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 3 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 15 — long-season crops need about 90 days of runway, quick greens only 30. Even here the calendar’s edges hold value: thirty-day greens late in the window, then garlic and a rested bed for spring.
Documented around Custer County
- monarch butterfly1 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Custer County
USGS estimates 4,922 lb of Glyphosate on Custer County farmland in 2019, its largest by weight, ahead of 2,4-d (4,298 lb) and Bromoxynil (848 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 Custer County — and how to grow with it.
We checked the federal record across Custer County — 589 documented sites across 6 of the 9 source types we track.
The most significant on record: 6 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Custer 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 Custer County
Closest first, across Custer County. Listing isn't leaking, and distance isn't exposure.
- Stanley Creek PlacerMining · 3.1 mi
- Sulphide ProspectMining · 5.4 mi
- Muleshoe ProspectMining · 5.7 mi
- Williams, Rohlds, and Ernst MineMining · 5.8 mi
- Silver Bell MineMining · 5.9 mi
- 12N 19E 19BAD1Nitrate · 6.0 mi
- 10N 18E 24ABA1Nitrate · 6.0 mi
- CLAYTON SILVER MINESUnderground Storage Tanks · 6.2 mi
- Last Chance MineMining · 6.7 mi
- Maude and Vermont LodesMining · 6.7 mi
- Pedrino ProspectMining · 6.8 mi
- Turtle MineMining · 7.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Custer 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 Custer County.
Sources Checked
across Custer County
Severity Distribution
across Custer County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Custer County, Mining runs higher than the national average — 434 sites across Custer County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Custer 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 Custer County average
Your land is one point inside Custer County
Everything above resolves to Custer County as a whole — one PHZM band and one county frost record, read across 3.2M 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 Custer County Average
Custer County Average
- ●USDA Zones 6a, averaged across Custer County
- ●One soil character for all of Custer County
- ●Frost dates read at Custer County's scale: Jun 3 to Sep 15
YOUR Parcel
- ✓Your exact zone, not Custer County's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Custer County
Pull a site-specific report for your exact address in Custer County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Custer County averages can't show:
We read public map data around Custer County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Custer County average
How we know this about Custer 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 Custer County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Custer County
When does frost risk typically end in Custer County?
The last hard freeze (28°F) in Custer County typically lands around Jun 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 Jun 24.
How long is the growing season in Custer County?
Measured between 28°F hard freezes, Custer County sees about 104 frost-free days — roughly Jun 3 through Sep 15, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 24 to Sep 1, about 69 days.
Is the soil safe to grow vegetables in Custer County?
The federal record around Custer County runs heavier than most — 589 documented sites, mostly Mining entries (434), the nearest Mining record about 3.1 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 Custer County?
With about 104 frost-free days between hard freezes, Custer 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 132 to 160 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 3 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Custer County's scale — its 6a band and its 104-day season. Your yard writes its own version of Custer 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 Custer County’s own scale
9 of the readings below were taken at Custer County's own scale — its own ~104-day span between 28°F freezes, the 3 most extensive soil series mapped here and 589 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Custer County's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Custer County's own 28°F hard-freeze dates and its ~104-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Custer CountyUSDA NRCS SSURGO
- 589 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 3.1 miles outFederal environmental registers
- Custer County's boundary and the 3,150,190 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~104-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Custer County spans, Idaho Batholith the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Custer County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Custer 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 Custer County — the ~104 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 Custer County's 3,150,190 acreswhy one lot differs from the next →
- Which of those 589 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 Custer Countyread your own land →