Arco, Idaho, sits in USDA hardiness zone 5a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Growers here do well with cabbage, cranberry, lavender, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Even in Arco, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Arco lot. 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 Arco — soil, climate, flood, and parcel records. How we handle your address.
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Arco — the short answer
Arco, Idaho: USDA zone 5a, about 128 days between hard freezes, across 684 acres of city.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 23
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~128
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 684 acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 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 Arco's average, not your lot's — a low corner or a tree line moves it. Against Arco's 128-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Arco
Each reading below is measured for Arco itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredArco runs about 128 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
MeasuredArco 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 Arco is in
Arco sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Arco's own centroid rather than borrowed from Butte County.
What Grows in Arco
Every plant below cleared Arco's own zone 5a and its 128-day season. Each card opens that plant's Idaho profile. How we score.
Is it too late to plant in Arco?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Apr 20; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 18 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 23 — long-season crops need about 90 days of runway, quick greens only 30. Short seasons reward decisiveness — quick-maturing varieties late, hardy greens under cover, and next year’s garlic in the ground before it closes.
What's on the federal record near Arco
Closest first, within ~10 miles of Arco. Listing isn't leaking, and distance isn't exposure.
- CRATERS OF THE MOON NATIONAL MONUMENTUnderground Storage Tanks · 700 ft
- BUTTE COUNTY ROAD & BRIDGEUnderground Storage Tanks · 700 ft
- ARCO MTCE YARDUnderground Storage Tanks · 700 ft
- ARCO SECTIONUnderground Storage Tanks · 700 ft
- EAST BUTTEUnderground Storage Tanks · 850 ft
- BUS MAINTENANCE SHOPUnderground Storage Tanks · 950 ft
- IDAHO TRANSPORTATION DEPTUnderground Storage Tanks · 1200 ft
- SUBURBAN PROPANEUnderground Storage Tanks · 1200 ft
- 04N 26E 36ACB1 ARCO CITY WELL 4Nitrate · 1200 ft
- ARCO SERVICEUnderground Storage Tanks · 1300 ft
- ARCO CHEVRON/VALLEY INSURANCE CENTERUnderground Storage Tanks · 1300 ft
- ARCO PHILLIPS 66Underground Storage Tanks · 1400 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Arco'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 Arco.
Severity Distribution
within ~10 miles of Arco
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Arco, Nitrate runs higher than the national average — 46 sites within ~10 miles of Arco. 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 Arco
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 Arco average
Your land is one point inside Arco
Everything above resolves to Arco as a whole — one PHZM band and one 28°F frost record, read across 684 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 city 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 local average.
Your Lot vs the Arco Average
Arco Average
- ●USDA Zones 5a, averaged across Arco
- ●One soil character for all of Arco
- ●Frost dates read at Arco's scale: May 18 to Sep 23
YOUR Parcel
- ✓Your exact zone, not Arco's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Arco
Pull a site-specific report for your exact address in Arco, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Arco averages can't show:
We read public map data around Arco — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Arco average
How we know this about Arco
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Arco’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Arco
When does frost risk typically end in Arco?
The last hard freeze (28°F) in Arco typically lands around May 18, 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 8.
When is the first frost in Arco?
The first hard freeze (28°F) in Arco typically arrives around Sep 23, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 9, so the watching starts about Aug 24 — about 128 days after the spring freeze cleared.
How long is the growing season in Arco?
Measured between 28°F hard freezes, Arco sees about 128 frost-free days — roughly May 18 through Sep 23, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 8 to Sep 9, about 93 days.
Is the soil safe to grow vegetables in Arco?
The federal record around Arco shows 74 documented sites, mostly Nitrate entries (46), the nearest Underground Storage Tanks record about 0.1 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.
How do gardeners stretch the season in Arco?
With about 128 frost-free days between hard freezes, Arco 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 156 to 184 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 18 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Arco's scale — its 5a band and its 128-day season. Your yard writes its own version of Arco's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Arco’s own scale
6 of the readings below were taken at Arco's own scale — its own ~128-day season between 28°F freezes, the 684 acres it covers and 74 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Arco's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Arco's own 28°F hard-freeze dates, about May 18 and Sep 23 and the ~128-day span between themNOAA 1991–2020 Climate Normals
- 74 documented contamination sites on the federal record near Arco, the closest Underground Storage Tanks record about 0.1 miles out from the town centreFederal environmental registers
- Arco's boundary and the 684 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~128-day seasonGrowable Ground crop-matching engine
- The ecoregion at Arco's own centroid, the Middle RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Arco's 684 acres read through its county's SSURGO summaryfrom Butte County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Butte County
- The growing challenges every Idaho grower plans around — written at state scale, so they stay on the state guidefrom Idaho
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Butte County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Arco's 684 acreswhy one lot differs from the next →
- Which side of Arco you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 684 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.1 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Arco-wide figureread your own land →
More in Idaho
Wider growing context
What grows across IdahoArco sits outside our named growing regions, so Idaho as a whole is its closest context here.
Nearby growing guides