Unlikely — Zone Mismatch
true yam (zones 9-12) does not overlap with Tennessee's zone range (6a-8a). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
True Yam is hardy to zone 9, and the warmest ground in Tennessee is zone 8 — 1 zone short. Planted in open ground it will not survive a Tennessee winter. To grow it here, grow true yam in a hoop house or unheated greenhouse — its modeled 1.5-zone lift covers this gap.
A hoop house or unheated greenhouse is the lift this needs. How a greenhouse changes what you can grow →
Zone math from 9-12 (plant) against 6-8 (Tennessee). Lift modeled by crop_engine.GREENHOUSE_ZONE_MODIFIER_BY_SUBTYPE['hoop_house'] (+1.5 zones) via api/fast_sections.py Unlock Engine v2.
True Yam in Tennessee — the short answer
True Yam in Tennessee: hardy in zones 9–12, full sun, against a state median of ~230 frost-free days.
- Plant zones
- 9-12
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Tennessee zones
- 6a-8a
- USDA PHZM 2023
- Frost window
- Mar 21 - Mar 29 – Nov 5 - Nov 12
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 193 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.
Tennessee spans zones 6a-8a, but your yard has its own microclimate — slope, trees, and low spots shift frost and sun across a single parcel. Enter your address and we'll score true yam against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Tennessee is not one climate
A single Tennessee answer averages 95 counties whose growing seasons are 73 days apart — from 193 frost-free days in Johnson County to 266 in Shelby County. Which end of that your land sits nearer changes what true yam can finish before the first hard freeze.
The middle half of 95 counties runs 221–235 days, with a median of 230 days — a 73-day span end to end.
Measured across 95 Tennessee counties. NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze. 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 True Yam Stands in Tennessee
True Yam is rated for zones 9–12 — a cold floor USDA puts at 20 to 30°F. No Tennessee county sits inside it, so in open ground this is a grown-under-cover plant here rather than a bed plant — which is a statement about Tennessee winters, not about true yam.
Below the zone 9 floor
95 counties
- Carter County · zone 7a
- Cheatham County · zone 7a
- Claiborne County · zone 7a
3 of 95 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.
Zone Comparison
True Yam Needs
- USDA Zones: 9-12
- Frost-Free Days: 220+
- Sun: Full Sun
- Mature size: 10 ft tall
- Picking window: ~30 days of harvest
- Drought tolerance: Medium
Tennessee Has
- USDA Zones: 6a-8a
- Last Hard Freeze (28°F): Mar 21 - Mar 29
- First Hard Freeze (28°F): Nov 5 - Nov 12
- Annual Rainfall: 45-55 inches
- Common Soils: Silt loam, Clay loam, Limestone-derived
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 Tennessee
The frost window
Across Tennessee, the last spring hard freeze (28°F) clears between Mar 21 and Mar 29, and the first fall hard freeze lands between Nov 5 and Nov 12 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 221-day window you can count on — up to 236 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.
Frost tenderness
True Yam is frost-tender — FAO ECOCROP puts its killing temperature at 48.2°F — so set plants out two to three weeks PAST your local last hard freeze, not on it and not on the state's earliest date. The 28°F marker above is when killing freezes stop, not when light frost does. That is the point where cold damages growing tissue, not a winter-survival floor — an established perennial comes through far colder while dormant, which is what its hardiness zone tells you.
Days to maturity vs. the window
At 270 days to maturity (Growable Ground Plant Database), even Tennessee's kindest 236-day season runs short — challenging without season extension. An indoor start plus row cover on both shoulders of the season closes the gap.
Timing tuned to sub-state frost dates — Johnson County, not the statewide average.
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 does not survive a Tennessee winter in the ground. The season figures below measure a different question — whether it could finish a season here at all — and they only bear on Tennessee under protection.
Frost-free days
True Yam wants 220+ frost-free days; a typical Tennessee site sees ~230 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves a tight window — use transplants and pick early-maturing cultivars.
Growing degree days
True Yam needs ~4000 GDD (base 50°F) to ripen. The state median runs ~4122 GDD (from PRISM 1991-2020 climate normals), so Tennessee sits right at the threshold — pay attention to siting and microclimate.
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 Tennessee. 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 Tennessee soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Tennessee site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Whether true yam is safe to eat from Tennessee soil is a block-by-block question, not a town-wide one — 28,130 documented contamination sites mean levels spike on some parcels and not the one next door. True Yam roots to about 59 inches, so it is the top 59 inches under your address that decide what it takes up, so only a test on your address settles it.
Check your parcel → Source: USDA NRCS SSURGO + EPA/state contamination databases.
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. Tennessee 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 Tennessee’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 Tennessee — and how to grow with it.
We checked the federal record across Tennessee — 28,130 documented sites across 8 of the 9 source types we track.
The most significant on record: 321 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Tennessee 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 Checked
across Tennessee
Severity Distribution
across Tennessee
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Tennessee, two things run higher than the national average across Tennessee — PFAS (262 sites) and Toxics Release Inventory (1,955 sites). That's not a problem with your land — it's information about it.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What Else to Consider for True Yam in Tennessee
Zone compatibility tells you about winter cold survival — but Tennessee growers also need to think about:
Heavy clay soils in the Nashville Basin
High humidity promotes disease in summer
Variable spring weather with late frost risk
Growing true yam here specifically
True Yam is a root crop whose edible part grows in or against the soil and can take up lead, and Tennessee carries 28,130 documented contamination sites where legacy fill and old paint push metals up parcel by parcel.
Grow true yam in raised beds of tested clean soil and run a parcel soil-lead test before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Tennessee grower, not just true yam — is covered on the Tennessee growing guide.
Timing shifts within Tennessee
Tennessee isn't one climate. In Johnson County, the last hard freeze (28°F) holds until about Apr 14 — roughly 21 days later than the recorded state median — so plant true yam to your county's window, not the statewide date.
True Yam needs about 220 days of frost-free season to complete its cycle. 75 of Tennessee’s 95 counties give it that outright. The tightest that does is Hawkins County at 220 frost-free days — 0 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
Across Tennessee’s 95 counties the frost-free season runs from 193 days in Johnson County to 266 days in Shelby County — a spread of 73 days, which is why a single statewide planting date misleads. The median Tennessee county sees 230 frost-free days, leaving true yam about 10 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). True Yam's 220-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
True Yam draws native bees (low value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, true yam can only work that bloom inside Tennessee's frost window — roughly 230 days, opening after the last 28°F freeze (Mar 21 - Mar 29) and closing at the first (Nov 5 - Nov 12), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant True Yam
True Yam is listed as toxic to dogs, cats (all) at a mild level (Cornell). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear. Worth knowing for placement: in Tennessee this is a one-season plant and the first hard freeze (Nov 5 - Nov 12) takes it down, so the exposure above is a summer-long one rather than something standing in the bed all year.
Tennessee Cooperative Extension
For Tennessee-specific cultivar recommendations, planting calendars, and pest pressure for true yam, the canonical source is UT Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is True Yam native to Tennessee?
No — the USDA PLANTS Database lists True Yam as introduced rather than native in the Lower 48, so it is not part of Tennessee's native flora. It grows here as a garden plant; pairing it with a few Tennessee natives keeps local pollinators fed too.
Looking for plants that belong here? The Tennessee growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing True Yam in Tennessee
When can I plant True Yam in Tennessee?
Tennessee's last spring hard freeze (28°F) clears between Mar 21 and Mar 29, and the first fall hard freeze lands between Nov 5 and Nov 12 (NOAA Regional Climate Centers ACIS, 1991-2020). True Yam is frost-tender — its killing temperature is 48.2°F (FAO ECOCROP — the point where cold damages growing tissue, not a winter-survival floor) — so wait two to three weeks past your site's last hard freeze, when light frost has also stopped, before planting out.
Can True Yam mature before first frost in Tennessee?
True Yam needs 270 days to mature (Growable Ground Plant Database), and even Tennessee's longest typical season runs 236 days (NOAA Regional Climate Centers ACIS, 1991-2020) — challenging without season extension. An indoor start plus row cover on both season shoulders closes the gap.
What hardiness zone is True Yam grown in across Tennessee?
Tennessee spans USDA hardiness zones 6a-8a (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 Tennessee site have?
A typical Tennessee site sees ~230 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. In cooler counties like Johnson, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is True Yam native to Tennessee?
No — the USDA PLANTS Database lists True Yam as introduced rather than native in the Lower 48, so it is not part of Tennessee's native flora. It grows here as a garden plant; pairing it with a few Tennessee natives keeps local pollinators fed too.
How should I amend the soil for True Yam in Tennessee?
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 Tennessee site — amend for drainage and organic matter first.
Will True Yam actually grow on my specific land in Tennessee?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores true yam against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Tennessee
State-level data is a sketch. Your Growable Ground report scores true yam against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Tennessee true yam averages can't show:
We read public map data around Tennessee — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Tennessee true yam average
Explore More
Growing guides for true yam
Explore Tennessee county by county
Tennessee carries 95 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 Tennessee 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 Tennessee
Tennessee has a growing page for 1,020 plants — a rotating sample of the rest of the shelf.
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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