Oso, Washington, sits in USDA hardiness zone 8a — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
These conditions suit cabbage, fig, california poppy, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Even in Oso, 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 Oso 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 Oso — soil, climate, flood, and parcel records. How we handle your address.
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Oso — the short answer
Oso, Washington: USDA zone 8a, about 264 days between hard freezes, across 2K acres of town.
- USDA zone
- 8a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 5
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 24
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~264
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 2K 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 8a is Oso's average, not your lot's — a low corner or a tree line moves it. Against Oso's 264-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Oso
Each reading below is measured for Oso itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredOso runs about 264 days between hard freezes — close to year-round growing.
Frost is rarely the limit here; winter plantings are as real as summer ones, and the harder question is which crops shrug off the summer heat.
Grow cool-season crops through the mild winter, and choose heat-tolerant varieties for the summer beds.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredOso sits in USDA hardiness zone 8a.
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 Oso is in
Oso sits in the North Cascades — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Oso's own centroid rather than borrowed from Snohomish County.
What Grows in Oso
Every plant below cleared Oso's own zone 8a and its 264-day season. Each card opens that plant's Washington profile. How we score.
Is it too late to plant in Oso?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Feb 5; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 5 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 24 — long-season crops need about 90 days of runway, quick greens only 30. And with a calendar this mild, the honest answer is that planting barely stops — winter opens seasons colder regions never see.
What's on the federal record near Oso
Closest first, within ~10 miles of Oso. Listing isn't leaking, and distance isn't exposure.
- F R BRADLEY LOGGING CO INCUnderground Storage Tanks · 2000 ft
- 32N/07E-09B01Nitrate · 2200 ft
- OSO General StoreUnderground Storage Tanks · 1.0 mi
- 32N/07E-08Q02 MW-SU-029Nitrate · 1.3 mi
- HIGHLAND CLEANERSUnderground Storage Tanks · 2.6 mi
- 32N/07E-12M01Nitrate · 2.8 mi
- Ernest Miller ProspectMining · 3.6 mi
- 32N/06E-11K01Nitrate · 3.9 mi
- US NAVY RADIO STATION JIM CREEKBrownfields · 4.3 mi
- US NAVY RADIO STATION JIM CREEKSuperfund · 4.3 mi
- Old Gray MareMining · 4.9 mi
- ARLINGTON WATER DEPTPFAS · 4.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Oso'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 Oso.
Total Sites
61
within ~10 miles of Oso
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Oso
Severity Distribution
within ~10 miles of Oso
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Oso, two things run higher than the national average within ~10 miles of Oso — Nitrate (42 sites) and Mining (4 sites). 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.
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 well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Oso
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 Oso average
Your land is one point inside Oso
Everything above resolves to Oso as a whole — one PHZM band and one 28°F frost record, read across 2K 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 town 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 Oso Average
Oso Average
- ●USDA Zones 8a, averaged across Oso
- ●One soil character for all of Oso
- ●Frost dates read at Oso's scale: Mar 5 to Nov 24
YOUR Parcel
- ✓Your exact zone, not Oso's 8a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Oso
Pull a site-specific report for your exact address in Oso, Washington — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Oso averages can't show:
We read public map data around Oso — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Oso average
How we know this about Oso
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Oso’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 town grain anywhere on this page — there is no town-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 Oso
When does frost risk typically end in Oso?
The last hard freeze (28°F) in Oso typically lands around Mar 5, 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 Mar 26.
When is the first frost in Oso?
The first hard freeze (28°F) in Oso typically arrives around Nov 24, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 10, so the watching starts about Oct 25 — about 264 days after the spring freeze cleared.
How long is the growing season in Oso?
Measured between 28°F hard freezes, Oso sees about 264 frost-free days — roughly Mar 5 through Nov 24, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 26 to Nov 10, about 229 days.
Is the soil safe to grow vegetables in Oso?
The federal record around Oso is a meaningful one — 61 documented sites, mostly Nitrate entries (42), the nearest Underground Storage Tanks record about 0.4 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Oso?
From about Oct 25 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Nov 24 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Nov 24. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Oso's scale — its 8a band and its 264-day season. Your yard writes its own version of Oso'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 Oso’s own scale
6 of the readings below were taken at Oso's own scale — its own ~264-day season between 28°F freezes, the 1,795 acres it covers and 61 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Oso's own USDA hardiness band, zones 8aUSDA PHZM 2023
- Oso's own 28°F hard-freeze dates, about Mar 5 and Nov 24 and the ~264-day span between themNOAA 1991–2020 Climate Normals
- 61 documented contamination sites on the federal record near Oso, the closest Underground Storage Tanks record about 0.4 miles out from the town centreFederal environmental registers
- Oso's boundary and the 1,795 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 8a and a ~264-day seasonGrowable Ground crop-matching engine
- The ecoregion at Oso's own centroid, the North CascadesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Oso's 1,795 acres read through its county's SSURGO summaryfrom Snohomish County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Snohomish County
- The growing challenges every Washington grower plans around — written at state scale, so they stay on the state guidefrom Washington
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Snohomish County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Oso's 1,795 acreswhy one lot differs from the next →
- Which side of Oso you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 1,795 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.4 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 Oso-wide figureread your own land →