Unlikely — Zone Mismatch
swamp mahogany (zones 9-11) does not overlap with Oklahoma's zone range (6b-8b). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
Swamp Mahogany is hardy to zone 9, and the warmest ground in Oklahoma is zone 8 — 1 zone short. Planted in open ground it will not survive a Oklahoma winter. To grow it here, grow swamp mahogany in a container and move it under cover for the coldest weeks, or give it a greenhouse.
Season extension and overwintering under cover both work at this margin. How to buy the weeks →
Zone math from 9-11 (plant) against 6-8 (Oklahoma). 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.
Oklahoma spans zones 6b-8b, 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 swamp mahogany against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Swamp Mahogany Needs
- USDA Zones: 9-11
- Frost-Free Days: 240+
- Sun: Full Sun
- Mature size: 160 ft tall
- Drought tolerance: Low
Oklahoma Has
- USDA Zones: 6b-8b
- Last Hard Freeze (28°F): Mar 15 - Mar 26
- First Hard Freeze (28°F): Nov 9 - Nov 14
- Annual Rainfall: 15-56 inches
- Common Soils: Red clay, Sandy loam, Prairie loam
Plant Zone Range (zones 9-11)
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 Swamp Mahogany in Oklahoma
The frost window
Across Oklahoma, the last spring hard freeze (28°F) clears between Mar 15 and Mar 26, and the first fall hard freeze lands between Nov 9 and Nov 14 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 228-day window you can count on — up to 244 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
Oklahoma runs as cold as USDA zone 6, and no sourced winter-hardiness floor is on record for swamp mahogany, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether swamp mahogany is a permanent planting or a replant-every-spring crop for you turns on your own zone within Oklahoma; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Cimarron 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 swamp mahogany does not survive a Oklahoma 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 Oklahoma under protection.
Frost-free days
Swamp Mahogany wants 240+ frost-free days; a typical Oklahoma site sees ~237 (NOAA Regional Climate Centers ACIS, 1991-2020) — 3 days short of what it needs. A typical Oklahoma 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
Swamp Mahogany likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across Oklahoma's red clay and sandy loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 6.5 — worth knowing before you decide whether a Oklahoma soil test result is a problem or just a number. Drainage matters: this plant wants poorly (saturated >50% of year), well (dry spells). If your Oklahoma site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Oklahoma's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. Swamp Mahogany needs about 59 inches of workable depth, so it is that horizon — not the surface — you are testing for. That map unit, not the state average, decides how swamp mahogany performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Oklahoma soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Swamp Mahogany in Oklahoma — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 9-11 (USDA PLANTS Database)
- State Zones: 6b-8b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 15 - Mar 26 to Nov 9 - Nov 14 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Swamp Mahogany in Oklahoma
Zone compatibility tells you about winter cold survival — but Oklahoma growers also need to think about:
Extreme weather variability (tornadoes, ice storms, drought)
Red clay soils drain poorly in central OK
Low western rainfall requires irrigation
Growing swamp mahogany here specifically
Swamp Mahogany sends deep roots and rates to zones 9–11, but much of Oklahoma sits on slow-draining, restrictive ground (SSURGO hydrologic group D) that forks and stunts them.
Loosen a deep, stone-free bed for swamp mahogany and break any compacted or hardpan layer before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Oklahoma grower, not just swamp mahogany — is covered on the Oklahoma growing guide.
Timing shifts within Oklahoma
Oklahoma isn't one climate. In Cimarron County, the last hard freeze (28°F) holds until about Apr 13 — roughly 24 days later than the recorded state median — so plant swamp mahogany to your county's window, not the statewide date.
Swamp Mahogany needs about 240 days of frost-free season to complete its cycle. 32 of Oklahoma’s 77 counties give it that outright. The tightest that does is Lincoln County at 240 frost-free days — 0 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
Across Oklahoma’s 77 counties the frost-free season runs from 197 days in Cimarron County to 267 days in Choctaw County — a spread of 70 days, which is why a single statewide planting date misleads. The median Oklahoma county sees 237 frost-free days, which is 3 days short of what swamp mahogany needs — so on a typical Oklahoma 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"). Swamp Mahogany's 240-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
Swamp Mahogany draws honeybees and native bees (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, swamp mahogany can only work that bloom inside Oklahoma's frost window — roughly 237 days, opening after the last 28°F freeze (Mar 15 - Mar 26) and closing at the first (Nov 9 - Nov 14), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant Swamp Mahogany
Swamp Mahogany is listed as toxic to dogs, cats (leaves) at a moderate level (ASPCA). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear.
Oklahoma Cooperative Extension
For Oklahoma-specific cultivar recommendations, planting calendars, and pest pressure for swamp mahogany, the canonical source is Oklahoma State University Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Swamp Mahogany native to Oklahoma?
No — the USDA PLANTS Database lists Swamp Mahogany as introduced rather than native in the Lower 48, so it is not part of Oklahoma's native flora. It grows here as a garden plant; pairing it with a few Oklahoma natives keeps local pollinators fed too.
Looking for plants that belong here? The Oklahoma 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 Swamp Mahogany in Oklahoma
When can I plant Swamp Mahogany in Oklahoma?
Oklahoma's last spring hard freeze (28°F) clears between Mar 15 and Mar 26, and the first fall hard freeze lands between Nov 9 and Nov 14 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Swamp Mahogany, so this page does not state whether it overwinters in Oklahoma 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 Swamp Mahogany grown in across Oklahoma?
Oklahoma spans USDA hardiness zones 6b-8b (USDA ARS PHZM 2023). Swamp Mahogany carries a range of zones 9-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Oklahoma site have?
A typical Oklahoma site sees ~237 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Swamp Mahogany needs 240+ 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 Cimarron, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Swamp Mahogany native to Oklahoma?
No — the USDA PLANTS Database lists Swamp Mahogany as introduced rather than native in the Lower 48, so it is not part of Oklahoma's native flora. It grows here as a garden plant; pairing it with a few Oklahoma natives keeps local pollinators fed too.
How should I amend the soil for Swamp Mahogany in Oklahoma?
Swamp Mahogany prefers pH 5.5-7.5 and poorly (saturated >50% of year), well (dry spells) drainage (FAO ECOCROP). That sits in the common-ground band across Oklahoma soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Swamp Mahogany actually grow on my specific land in Oklahoma?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores swamp mahogany 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 Oklahoma
State-level data is a sketch. Your Growable Ground report scores swamp mahogany against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Oklahoma swamp mahogany averages can't show:
We read public map data around Oklahoma — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Oklahoma swamp mahogany average
Explore More
Growing guides for swamp mahogany
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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