Ada County, in Idaho, sits in USDA hardiness zone 7a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Crops well matched to these conditions include cabbage, pawpaw, california poppy, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Ada County lies within the Treasure Valley and the Snake River Plain — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Ada County holds more than one microclimate.
Soils and elevations shift across Ada 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 Ada County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Ada County — the short answer
Ada County, Idaho: USDA zone 7a, about 205 days between hard freezes, across 673K acres.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 9
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 31
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~205
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 673K 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 7a is Ada County's average, not your lot's — a low corner or a tree line moves it. Against Ada County's 205-day season, see what your own ground reads.
Heat in Ada County
Across a year, Ada County accumulates about 2,664 growing degree days above 50°F, about 1,173 more than the middle Idaho county — ahead of 41 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 Ada County
Across Ada County, the ground is predominantly Aridisols, where Chilcott, Purdam, and Power are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 7.0–7.4, neutral. Rainfall drains through hydrologic group C soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
How the ground varies across Ada County
The USDA soil survey maps 84% of Ada County as well drained — but another 11% drains differently: 6% somewhat excessively drained, 3% somewhat poorly drained.
Chilcott is the most extensive named soil at 10% of mapped acres, then Purdam (7%) and Power (6%).
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 Ada County
Each reading below is measured for Ada 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 Ada 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 Ada County runs about pH 7.0–7.4, 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
MeasuredAda County runs about 205 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredAda County sits in USDA hardiness zone 7a.
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 Ada County is in
Ada County spans 2 EPA Level III ecoregions — Snake River Plain (93%) and Idaho Batholith (8%). 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 Ada County
We scored all 1,086 plants against Ada County's own USDA zone 7a and its own 205-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 Ada County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 12; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 31 — long-season crops need about 90 days of runway, quick greens only 30. With a season this long, “too late” mostly means “switch crops” — second sowings and a full fall garden are the norm, with garlic closing the year.
Documented around Ada County
- Japanese beetle2 documented records
- monarch butterfly6 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Ada County
USGS estimates 24,817 lb of Glyphosate on Ada County farmland in 2019, its largest by weight, ahead of Acetochlor (2,470 lb) and Metolachlor-s (2,296 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 Ada County — and how to grow with it.
We checked the federal record across Ada County — 2,791 documented sites across 8 of the 9 source types we track.
The most significant on record: 7 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Ada 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 Ada County
Closest first, across Ada County. Listing isn't leaking, and distance isn't exposure.
- 01N 02E 05CDC1Nitrate · 0.5 mi
- 01N 02E 06DDC1Nitrate · 0.8 mi
- 02N 02E 32DBA1Nitrate · 0.9 mi
- 01N 02E 06ABA2Nitrate · 0.9 mi
- 01N 02E 08ADA2-DESTROYEDNitrate · 0.9 mi
- 01N 02E 08ADA3Nitrate · 0.9 mi
- CS BEEF PACKERSToxics Release Inventory · 1.6 mi
- 02N 02E 34CCD1Nitrate · 1.7 mi
- IBP INCORPORATEDToxics Release Inventory · 1.8 mi
- 01N 01E 12DAA2Nitrate · 1.8 mi
- 01N 01E 12DAA1Nitrate · 1.9 mi
- DARLING INGREDIENTSToxics Release Inventory · 1.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Ada 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 Ada County.
Severity Distribution
across Ada County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Ada County, Nitrate runs higher than the national average — 1,592 sites across Ada County. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
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 Ada 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 Ada County average
Your land is one point inside Ada County
Everything above resolves to Ada County as a whole — one PHZM band and one county frost record, read across 673K 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 Ada County Average
Ada County Average
- ●USDA Zones 7a, averaged across Ada County
- ●One soil character for all of Ada County
- ●Frost dates read at Ada County's scale: Apr 9 to Oct 31
YOUR Parcel
- ✓Your exact zone, not Ada County's 7a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Ada County
Pull a site-specific report for your exact address in Ada County, Idaho — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Ada County averages can't show:
We read public map data around Ada County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Ada County average
How we know this about Ada 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 Ada County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Ada County
When does frost risk typically end in Ada County?
The last hard freeze (28°F) in Ada County typically lands around Apr 9, 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 Apr 30.
How long is the growing season in Ada County?
Measured between 28°F hard freezes, Ada County sees about 205 frost-free days — roughly Apr 9 through Oct 31, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 30 to Oct 17, about 170 days.
Is the soil safe to grow vegetables in Ada County?
The federal record around Ada County runs heavier than most — 2,791 documented sites, mostly Nitrate entries (1,592), the nearest Nitrate record about 0.5 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.
Everything above is measured at Ada County's scale — its 7a band and its 205-day season. Your yard writes its own version of Ada 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 Ada County’s own scale
9 of the readings below were taken at Ada County's own scale — its own ~205-day span between 28°F freezes, the 3 most extensive soil series mapped here and 2,791 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Ada County's own USDA hardiness band, zones 7aUSDA PHZM 2023
- Ada County's own 28°F hard-freeze dates and its ~205-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Ada CountyUSDA NRCS SSURGO
- 2,791 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 0.5 miles outFederal environmental registers
- Ada County's boundary and the 673,440 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~205-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Ada County spans, Snake River Plain the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Ada County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Ada 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 Ada County — the ~205 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 Ada County's 673,440 acreswhy one lot differs from the next →
- Which of those 2,791 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 Ada Countyread your own land →