Unlikely — Zone Mismatch
swamp mahogany (zones 9-11) does not overlap with New Jersey's zone range (6a-8a). 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 New Jersey is zone 8 — 1 zone short. Planted in open ground it will not survive a New Jersey 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 (New Jersey). 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.
New Jersey 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 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
New Jersey Has
- USDA Zones: 6a-8a
- Last Hard Freeze (28°F): Mar 26 - Apr 4
- First Hard Freeze (28°F): Nov 5 - Nov 17
- Annual Rainfall: 40-50 inches
- Common Soils: Sandy loam (Pine Barrens), Silt loam, Clay
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 New Jersey
The frost window
Across New Jersey, the last spring hard freeze (28°F) clears between Mar 26 and Apr 4, and the first fall hard freeze lands between Nov 5 and Nov 17 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 215-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
New Jersey 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 New Jersey; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Morris 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 New Jersey 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 New Jersey under protection.
Frost-free days
Swamp Mahogany wants 240+ frost-free days; a typical New Jersey site sees ~222 (NOAA Regional Climate Centers ACIS, 1991-2020) — 18 days short of what it needs. A typical New Jersey 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 New Jersey's sandy loam (pine barrens) and silt 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 New Jersey 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 New Jersey site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
SSURGO maps about 14.3% of New Jersey as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Swamp Mahogany has low drought tolerance, so it is the fast-draining end that will cost you — your soil map unit, not the state average, is the real answer.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. New Jersey soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Swamp Mahogany in New Jersey — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 9-11 (USDA PLANTS Database)
- State Zones: 6a-8a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 26 - Apr 4 to Nov 5 - Nov 17 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Swamp Mahogany in New Jersey
Zone compatibility tells you about winter cold survival — but New Jersey growers also need to think about:
Sandy Pine Barrens soils are nutrient-poor
Urban heat island effects in northern NJ
Deer browse is extreme in suburban areas
Growing swamp mahogany here specifically
Swamp Mahogany needs sharp drainage and sends deep roots hardy to about 41°F; in New Jersey, about 14.3% of soils are poorly-drained (SSURGO), and standing water is what actually kills it.
Build swamp mahogany up on a coarse, free-draining mound so its crown never sit in saturated soil. How to handle it →
What to actually do about these — and the constraints that apply to every New Jersey grower, not just swamp mahogany — is covered on the New Jersey growing guide.
Timing shifts within New Jersey
New Jersey isn't one climate. In Morris County, the last hard freeze (28°F) holds until about Apr 11 — roughly 11 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. 3 of New Jersey’s 21 counties give it that outright. The tightest that does is Cape May County at 241 frost-free days — 1 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
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 New Jersey's frost window — roughly 222 days, opening after the last 28°F freeze (Mar 26 - Apr 4) and closing at the first (Nov 5 - Nov 17), 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.
New Jersey Cooperative Extension
For New Jersey-specific cultivar recommendations, planting calendars, and pest pressure for swamp mahogany, the canonical source is Rutgers Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Swamp Mahogany native to New Jersey?
No — the USDA PLANTS Database lists Swamp Mahogany as introduced rather than native in the Lower 48, so it is not part of New Jersey's native flora. It grows here as a garden plant; pairing it with a few New Jersey natives keeps local pollinators fed too.
Looking for plants that belong here? The New Jersey 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 New Jersey
When can I plant Swamp Mahogany in New Jersey?
New Jersey's last spring hard freeze (28°F) clears between Mar 26 and Apr 4, and the first fall hard freeze lands between Nov 5 and Nov 17 (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 New Jersey 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 New Jersey?
New Jersey spans USDA hardiness zones 6a-8a (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 New Jersey site have?
A typical New Jersey site sees ~222 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 Morris, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Swamp Mahogany native to New Jersey?
No — the USDA PLANTS Database lists Swamp Mahogany as introduced rather than native in the Lower 48, so it is not part of New Jersey's native flora. It grows here as a garden plant; pairing it with a few New Jersey natives keeps local pollinators fed too.
How should I amend the soil for Swamp Mahogany in New Jersey?
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 New Jersey 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 New Jersey?
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 New Jersey
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 New Jersey swamp mahogany averages can't show:
We read public map data around New Jersey — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the New Jersey 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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