Conditional — Some Areas
true yam (zones 9-12) reaches only part of Oregon (5a-10a): zones 9-10 are in range, so where you are in the state decides it.
True Yam in Oregon — the short answer
True Yam in Oregon: hardy in zones 9–12, full sun.
- Plant zones
- 9-12
- Not verified
- Oregon zones
- 5a-10a
- USDA PHZM 2023
- Frost window
- Feb 25 - Apr 26 – Oct 19 - Nov 26
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 86 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 270 days
- Growable Ground Plant Database
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
Oregon spans zones 5a-10a, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score true yam against your parcel's actual hardiness, soil, and sun.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your parcel report in seconds — read in full free for your first 14 days
Oregon is not one climate
Oregon’s winter-low ladder runs across 36 counties, from zone 6 in Klamath County to zone 9.5 in Curry County. That is 35°F between the two counties’ average coldest night — the difference between true yam overwintering in the ground and coming under cover.
The middle half of 36 counties runs 6.5–8.5 zones, with a median of 7.5 zones — a 3.5-zone span end to end.
Measured across 36 Oregon counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where in Oregon Fits Best
True Yam is rated for zones 9–12 — a cold floor USDA puts at 20 to 30°F. Against Oregon’s 36 counties that band holds in 5 of them, and the line runs at Coos County (zone 9a), the coldest county still inside it.
Below the zone 9 floor
31 counties
- Klamath County · zone 6a
- Baker County · zone 6b
- Crook County · zone 6b
3 of 31 shown
Winter cold is the limit here — the same plant works in a container that comes under cover.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Even within Oregon's zones 5a-10a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for true yam (USDA PHZM 2023):
Zone Comparison
True Yam Needs
- USDA Zones: 9-12
- Sun: Full Sun
- Mature size: 10 ft tallWe haven't confirmed this against a published source yet.
- Picking window: ~30 days of harvestWe haven't confirmed this against a published source yet.
- Drought tolerance: MediumWe haven't confirmed this against a published source yet.
Oregon Has
- USDA Zones: 5a-10a
- Last Hard Freeze (28°F): Feb 25 - Apr 26
- First Hard Freeze (28°F): Oct 19 - Nov 26
- Annual Rainfall: 8-90 inches
- Common Soils: Volcanic, Silt loam (Willamette), Sandy loam
Plant Zone Range (zones 9-12)
Preferred Soil pH
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant True Yam in Oregon
The frost window
Across Oregon, the last spring hard freeze (28°F) clears between Feb 25 and Apr 26, and the first fall hard freeze lands between Oct 19 and Nov 26 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 176-day window you can count on — up to 274 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
Winter standing
Oregon runs as cold as USDA zone 5, and no sourced winter-hardiness floor is on record for true yam, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether true yam is a permanent planting or a replant-every-spring crop for you turns on your own zone within Oregon; check its hardiness range against that before treating it as long-lived ground.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says true yam survives winter in part of Oregon, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Growing degree days
True Yam needs ~4000 GDD (base 50°F) to ripen. We haven't confirmed this against a published source yet. The state median runs ~1666 GDD (from PRISM 1991-2020 climate normals), so Oregon's typical season runs short on heat — pick a south-facing site and consider season extension.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
True Yam tolerates a wide pH range (pH 4.8-8.5) — 3.7 units, acid ground through alkaline — so soil acidity is rarely what limits it in Oregon. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 5.5 and 6.5 — worth knowing before you decide whether a Oregon soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Oregon site is heavier clay or sits in a low spot, a raised bed lifts the roots above wet ground, or work in compost.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. Oregon soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant true yam for food
Anything you grow to eat takes up what is in the ground it grows in, so what is on record near you is worth knowing before true yam goes in. What follows is Oregon’s documented federal record at state scale — a screening signal, not a soil test, and not a statement about any one lot.
Safe to Grow Here?
What the federal record shows across Oregon — and how to grow with it.
We checked the federal record across Oregon — 16,374 documented sites across 7 of the 8 source types we track.
The most significant on record: 260 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Oregon 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 of imported, lab-tested soil grow well almost anywhere in the meantime.
Sources Checked
across Oregon
Severity Distribution
across Oregon
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Oregon, Mining runs higher than the national average — 3,562 sites across Oregon. That's not a problem with your land — it's information about 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.
Sources: EPA, USGS — 950K documented sites tracked nationwide across 8 federal source types.
What Else to Consider for True Yam in Oregon
Zone compatibility tells you about winter cold survival — but Oregon growers also need to think about:
West side: excessive rain and overcast skies reduce sun for warm-season crops
East side: arid conditions (8-15 inches rainfall) require irrigation
Slug pressure is extreme in western Oregon
Mountain areas have very short seasons (60-90 frost-free days)
What to actually do about these — and the constraints that apply to every Oregon grower, not just true yam — is covered on the Oregon growing guide.
Where in Oregon True Yam Is Zone-Hardy
True Yam is rated for USDA zones 9–12. 5 of Oregon’s 36 counties fall inside that band. The coldest that does is Coos County at zone 9a. 31 counties sit below the plant’s zone 9 floor, where an unprotected plant is relying on snow cover and a mild year. Where you are in Oregon decides this one.
Across those 36 counties Oregon’s winter-low ladder runs from zone 6a in Klamath County to zone 9b in Curry County — 3.5 USDA zones of spread, which is 35°F between the two counties’ average coldest night of the year. That is why a statewide hardiness answer is where you start and not where you finish.
The planting window moves with it. Klamath County holds its last hard freeze (28°F) until about Jun 9, while Lincoln County is clear by Feb 3 — 126 days apart. Set true yam out on your county’s date, not the state’s.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. County last-freeze dates: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F killing freeze — earlier than the folk 32°F "last frost". True Yam’s zone 9–12 band: Not verified. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Pollinator + Wildlife Value
True Yam draws native bees (low value). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, true yam can only work that bloom inside Oregon's frost window — roughly 213 days, opening after the last 28°F freeze (Feb 25 - Apr 26) and closing at the first (Oct 19 - Nov 26), per NOAA Regional Climate Centers ACIS, 1991-2020. Pollinator value: We haven't confirmed this against a published source yet.
Oregon Cooperative Extension
For Oregon-specific cultivar recommendations, planting calendars, and pest pressure for true yam, the canonical source is OSU Extension Service. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is True Yam native to Oregon?
No — the USDA PLANTS Database lists True Yam as introduced rather than native in the Lower 48, so it is not part of Oregon's native flora. It grows here as a garden plant; pairing it with a few Oregon natives keeps local pollinators fed too.
Looking for plants that belong here? The Oregon growing guide lists plants that USDA PLANTS records growing in Oregon and that Kew and NatureServe Explorer both list in its native range, leaving out any that NatureServe flags as exotic there or that our audit holds.
State records: USDA PLANTS Database state-distribution data (presence, not state-level nativity), accessed 2026-10-19.
Common Questions About Growing True Yam in Oregon
When can I plant True Yam in Oregon?
Oregon's last spring hard freeze (28°F) clears between Feb 25 and Apr 26, and the first fall hard freeze lands between Oct 19 and Nov 26 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for True Yam, so this page does not state whether it overwinters in Oregon and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is True Yam grown in across Oregon?
Oregon spans USDA hardiness zones 5a-10a (USDA ARS PHZM 2023). True Yam carries a range of zones 9-12, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Oregon site have?
A typical Oregon site sees ~213 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). True Yam needs 220+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is True Yam native to Oregon?
No — the USDA PLANTS Database lists True Yam as introduced rather than native in the Lower 48, so it is not part of Oregon's native flora. It grows here as a garden plant; pairing it with a few Oregon natives keeps local pollinators fed too.
How should I amend the soil for True Yam in Oregon?
True Yam tolerates pH 4.8-8.5 and well (dry spells) drainage (FAO ECOCROP). That is a 3.7-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Oregon site — amend for drainage and organic matter first.
Will True Yam actually grow on my specific land in Oregon?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores true yam against your address's mapped soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Oregon
State-level data is a sketch. Your Growable Ground report scores true yam against your land's mapped soil, modelled sun, drainage, and frost data — not zone averages.
Three things about your lot that Oregon true yam averages can't show:
We read public map data around Oregon — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Oregon true yam average
Explore More
Growing guides for true yam
Explore Oregon county by county
Oregon carries 36 counties with their own USDA zone — a sample of the growing pages for true yam there:
Where else true yam grows
True Yam's zone band crosses state lines — these are the states closest to Oregon in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in Oregon
Oregon has a growing page for 1,033 plants — a rotating sample of the rest of the shelf.
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