Multnomah County, in Oregon, sits in USDA hardiness zone 9a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
On paper, artichoke, fig, california poppy, and cabbage all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Multnomah County lies within the Willamette Valley and the Pacific Northwest — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Multnomah County holds more than one microclimate.
Soils and elevations shift across Multnomah 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 Multnomah County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Multnomah County — the short answer
Multnomah County, Oregon: USDA zone 9a, about 292 days between hard freezes, across 276K acres.
- USDA zone
- 9a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Feb 13
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 2
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~292
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 276K 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 9a is Multnomah County's average, not your lot's — a low corner or a tree line moves it. Against Multnomah County's 292-day season, see what your own ground reads.
Heat and winter chill in Multnomah County
Across a year, Multnomah County accumulates about 2,400 growing degree days above 50°F, about 548 more than the middle Oregon county — ahead of 32 of Oregon’s 36 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.
Winter banks about 2,348 hours below 45°F. Chill is what tells a fruit tree its dormancy is over, and it is set by climate rather than by anything you can build.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Multnomah County
Across Multnomah County, the ground is predominantly Inceptisols, where Zygore, Cascade, and Goble are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 5.6–5.8, moderately acidic. Rainfall drains through hydrologic group B soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
6%
Hydric soils
14%
Soil still varies lot by lot — soil types explained.
How the ground varies across Multnomah County
The USDA soil survey maps 44% of Multnomah County as well drained — but another 31% drains differently: 12% somewhat poorly drained, 7% poorly drained.
Zygore is the most extensive named soil at 12% of mapped acres, then Cascade (10%) and Goble (8%).
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 Multnomah County
Each reading below is measured for Multnomah 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 Multnomah 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 Multnomah County runs about pH 5.6–5.8, on the acidic side.
Blueberries, potatoes, and rhododendrons thrive in it, but most vegetables start locking out nutrients below about pH 6.0 and grow pale and stunted no matter how much you feed them.
A measured lime application raises pH for the crops that need it — but test first, because the right rate depends on your own soil, not the county average.
USDA NRCS SSURGO
Season length
MeasuredMultnomah County runs about 292 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
MeasuredMultnomah County sits in USDA hardiness zone 9a.
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 Multnomah County is in
Multnomah County spans 3 EPA Level III ecoregions — Willamette Valley (55%), Cascades (38%) and Coast Range (7%). 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 Multnomah County
We scored all 1,086 plants against Multnomah County's own USDA zone 9a and its own 292-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 Oregon profile.
Is it too late to plant in Multnomah County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Jan 16; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Feb 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 2 — long-season crops need about 90 days of runway, quick greens only 30. Here the calendar nearly circles: cool-season crops take the winter shift, and the next window is always close.
Documented around Multnomah County
Survey cells within 31 miles of Multnomah County checked for spotted lanternfly, none carrying a detection — a surveyed negative, not an absence of looking. Nearest documented record 539 miles off. What to watch for.
- monarch butterfly5 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Multnomah County
USGS estimates 13,611 lb of Glyphosate on Multnomah County farmland in 2019, its largest by weight, ahead of Metolachlor-s (1,739 lb) and Metolachlor & Metolachlor-s (1,739 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 Multnomah County — and how to grow with it.
We checked the federal record across Multnomah County — 3,488 documented sites across 8 of the 9 source types we track.
The most significant on record: 58 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Multnomah 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 Multnomah County
Closest first, across Multnomah County. Listing isn't leaking, and distance isn't exposure.
- TROUTDALE TRANSFER STATIONBrownfields · 800 ft
- FAIRVIEW FARMS (OLD SITE)Underground Storage Tanks · 1800 ft
- CARVANA LLCBrownfields · 1800 ft
- GLACIER NORTHWEST INC TROUTDALE READY-MIX PLANTToxics Release Inventory · 1900 ft
- GLACIER NORTHWEST INC TROUTDALE READY-MIX PLANTBrownfields · 1900 ft
- WALMART SUPERCENTER 2927Brownfields · 2000 ft
- DALE KRUEGER'S (KRUEGER'S TRUCK STOP)Underground Storage Tanks · 2000 ft
- CHEVRON USA INC #98295Underground Storage Tanks · 2200 ft
- ARCO WOOD VILLAGEUnderground Storage Tanks · 2200 ft
- ARCO 6503Brownfields · 2200 ft
- AGC HEAT EXCHANGER INCBrownfields · 2500 ft
- MML DIAGNOSTICSBrownfields · 2500 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Multnomah 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 Multnomah County.
Severity Distribution
across Multnomah County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Multnomah County, Superfund runs higher than the national average — 58 sites across Multnomah County. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in Multnomah 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 Multnomah County average
Your land is one point inside Multnomah County
Everything above resolves to Multnomah County as a whole — one PHZM band and one county frost record, read across 276K 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 Multnomah County Average
Multnomah County Average
- ●USDA Zones 9a, averaged across Multnomah County
- ●One soil character for all of Multnomah County
- ●Frost dates read at Multnomah County's scale: Feb 13 to Dec 2
YOUR Parcel
- ✓Your exact zone, not Multnomah County's 9a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Multnomah County
Pull a site-specific report for your exact address in Multnomah County, Oregon — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Multnomah County averages can't show:
We read public map data around Multnomah County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Multnomah County average
How we know this about Multnomah 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 Multnomah County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Multnomah County
When does frost risk typically end in Multnomah County?
The last hard freeze (28°F) in Multnomah County typically lands around Feb 13, 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 6.
How long is the growing season in Multnomah County?
Measured between 28°F hard freezes, Multnomah County sees about 292 frost-free days — roughly Feb 13 through Dec 2, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 6 to Nov 18, about 257 days.
Is the soil safe to grow vegetables in Multnomah County?
The federal record around Multnomah County runs heavier than most — 3,488 documented sites, mostly Underground Storage Tanks entries (1,929), the nearest Brownfields record about 0.1 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.
Everything above is measured at Multnomah County's scale — its 9a band and its 292-day season. Your yard writes its own version of Multnomah 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 Oregon's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Multnomah County’s own scale
9 of the readings below were taken at Multnomah County's own scale — its own ~292-day span between 28°F freezes, the 3 most extensive soil series mapped here and 3,488 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Multnomah County's own USDA hardiness band, zones 9aUSDA PHZM 2023
- Multnomah County's own 28°F hard-freeze dates and its ~292-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Multnomah CountyUSDA NRCS SSURGO
- 3,488 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Brownfields record about 0.1 miles outFederal environmental registers
- Multnomah County's boundary and the 275,848 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9a and a ~292-day seasonGrowable Ground crop-matching engine
- The 3 ecoregions Multnomah County spans, Willamette Valley the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Multnomah County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Multnomah County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Oregon grower plans around — written at state scale, so they stay on the state guidefrom Oregon
What this page can’t tell you
- How the season shifts across Multnomah County — the ~292 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 Multnomah County's 275,848 acreswhy one lot differs from the next →
- Which of those 3,488 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 Multnomah Countyread your own land →