Unlikely — Zone Mismatch
ironwood (zones 10-13) does not overlap with Tennessee's zone range (6a-8a). Growing outdoors is unlikely without significant protection.
2 zones short — what would close it
Ironwood is hardy to zone 10, and the warmest ground in Tennessee is zone 8 — 2 zones short. Planted in open ground it will not survive a Tennessee winter. To grow it here, grow ironwood under glass — a greenhouse is the only lift this wide the engine models.
A greenhouse is the lift this needs. How a greenhouse changes what you can grow →
Zone math from 10-13 (plant) against 6-8 (Tennessee). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
Tennessee spans zones 6a-8a, 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 ironwood against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Ironwood Needs
- USDA Zones: 10-13
- Frost-Free Days: 365+
- Sun: Full Sun
- Drought tolerance: High
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 10-13)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Ironwood 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.
Winter standing
Tennessee runs as cold as USDA zone 6, and no sourced winter-hardiness floor is on record for ironwood, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether ironwood is a permanent planting or a replant-every-spring crop for you turns on your own zone within Tennessee; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Johnson County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. 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 ironwood 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
Ironwood wants 365+ frost-free days; a typical Tennessee site sees ~230 (NOAA Regional Climate Centers ACIS, 1991-2020) — 135 days short of what it needs. A typical Tennessee season does not carry this crop to harvest outdoors, and a gap that size is not one an earlier sowing date or a faster cultivar closes; growing it here means growing it under cover.
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
Ironwood likes near-neutral soil (pH 6.8-8.6). That's the common-ground band across Tennessee's silt loam and clay loam — a soil test confirms it for your site.
Your land, not the state average
Tennessee soil pH runs about 5.0–5.6, and that sits below ironwood's tolerated 6.8–8.6, so the typical Tennessee parcel needs lime before it will perform. SSURGO maps it swinging by full points parcel to parcel, so your map unit, not the state number, decides whether ironwood needs lime or sulfur.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Tennessee soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Ironwood in Tennessee — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 10-13 (USDA PLANTS Database)
- State Zones: 6a-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 21 - Mar 29 to Nov 5 - Nov 12 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Ironwood 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 ironwood here specifically
Ironwood wants soil pH 6.8–8.6, but Tennessee's soils run acidic (SSURGO maps a dominant pH near 5.3) — below its range, nutrients lock up and growth stalls.
Test your soil and lime to raise pH into ironwood's 6.8–8.6 range before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Tennessee grower, not just ironwood — 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 ironwood to your county's window, not the statewide date.
Ironwood needs about 365 days of frost-free season to complete its cycle. No Tennessee county gives it that outdoors: even Shelby County, the state’s longest season at 266 frost-free days, falls 99 days short — so it needs transplants, a short-season variety, or covered growing.
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, which is 135 days short of what ironwood needs — so on a typical Tennessee parcel this is a transplant-or-protect crop, not a direct-sow one.
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"). Ironwood's 365-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Tennessee Cooperative Extension
For Tennessee-specific cultivar recommendations, planting calendars, and pest pressure for ironwood, the canonical source is UT Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Ironwood native to Tennessee?
Ironwood is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Tennessee. It can still earn a place in a Tennessee garden — the zone comparison above tells you whether it will thrive.
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 Ironwood in Tennessee
When can I plant Ironwood 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). No sourced winter-hardiness floor is on record for Ironwood, so this page does not state whether it overwinters in Tennessee 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 Ironwood grown in across Tennessee?
Tennessee spans USDA hardiness zones 6a-8a (USDA ARS PHZM 2023). Ironwood carries a range of zones 10-13, 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). Ironwood needs 365+ 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 Ironwood native to Tennessee?
Ironwood is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Tennessee. It can still earn a place in a Tennessee garden — the zone comparison above tells you whether it will thrive.
How should I amend the soil for Ironwood in Tennessee?
Ironwood prefers pH 6.8-8.6 (USDA PLANTS). That sits in the common-ground band across Tennessee soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Ironwood actually grow on my specific land in Tennessee?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores ironwood 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 ironwood against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Tennessee ironwood 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 ironwood average
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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