Unlikely — Zone Mismatch
sour orange (zones 9-11) does not overlap with Rhode Island's zone range (6b-7b). Growing outdoors is unlikely without significant protection.
2 zones short — what would close it
Sour Orange is hardy to zone 9, and the warmest ground in Rhode Island is zone 7 — 2 zones short. Planted in open ground it will not survive a Rhode Island winter. To grow it here, grow sour orange in an earth-sheltered greenhouse — its modeled 2.5-zone lift covers this gap.
An earth-sheltered greenhouse is the lift this needs. How a greenhouse changes what you can grow →
Zone math from 9-11 (plant) against 6-7 (Rhode Island). Lift modeled by crop_engine.GREENHOUSE_ZONE_MODIFIER_BY_SUBTYPE['earth_sheltered'] (+2.5 zones) via api/fast_sections.py Unlock Engine v2.
Sour Orange in Rhode Island — the short answer
Sour Orange in Rhode Island: hardy in zones 9–11, full sun, against a state median of ~225 frost-free days.
- Plant zones
- 9-11
- 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
- Rhode Island zones
- 6b-7b
- USDA PHZM 2023
- Frost window
- Mar 27 - Apr 3 – Nov 7 - Nov 21
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 210 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
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.
Rhode Island spans zones 6b-7b, 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 sour orange 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.
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Where Sour Orange Stands in Rhode Island
Sour Orange is rated for zones 9–11 — a cold floor USDA puts at 20 to 30°F. No Rhode Island 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 Rhode Island winters, not about sour orange.
Below the zone 9 floor
5 counties
- Kent County · zone 6b
- Providence County · zone 6b
- Bristol County · zone 7a
3 of 5 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
Sour Orange Needs
- USDA Zones: 9-11
- Frost-Free Days: 140+
- Sun: Full Sun
- Picking window: ~28 days of harvest
Rhode Island Has
- USDA Zones: 6b-7b
- Last Hard Freeze (28°F): Mar 27 - Apr 3
- First Hard Freeze (28°F): Nov 7 - Nov 21
- Annual Rainfall: 44-52 inches
- Common Soils: Glacial till, Sandy loam, Coastal sand
Plant Zone Range (zones 9-11)
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 Sour Orange in Rhode Island
The frost window
Across Rhode Island, the last spring hard freeze (28°F) clears between Mar 27 and Apr 3, and the first fall hard freeze lands between Nov 7 and Nov 21 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 218-day window you can count on — up to 239 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
Rhode Island runs as cold as USDA zone 6, and no sourced winter-hardiness floor is on record for sour orange, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether sour orange is a permanent planting or a replant-every-spring crop for you turns on your own zone within Rhode Island; 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 sour orange does not survive a Rhode Island 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 Rhode Island under protection.
Frost-free days
Sour Orange wants 140+ frost-free days; a typical Rhode Island site sees ~225 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
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
Sour Orange likes near-neutral soil (pH 5.5-8.3). That's the common-ground band across Rhode Island's glacial till 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 7 — worth knowing before you decide whether a Rhode Island soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Rhode Island site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Rhode Island's soils run mostly fine sandy loam, but SSURGO maps the series, texture, and drainage under your exact parcel. Sour Orange 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 sour orange performs.
Check your parcel → Source: USDA NRCS SSURGO.
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. Rhode Island soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant sour orange 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 sour orange goes in. What follows is Rhode Island’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 Rhode Island — and how to grow with it.
We checked the federal record across Rhode Island — 7,250 documented sites across 7 of the 9 source types we track.
The most significant on record: 141 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Rhode Island 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 Rhode Island
Severity Distribution
across Rhode Island
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Rhode Island, two things run higher than the national average across Rhode Island — Superfund (141 sites) and Toxics Release Inventory (446 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
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 Sour Orange in Rhode Island
Zone compatibility tells you about winter cold survival — but Rhode Island growers also need to think about:
Small lot sizes limit garden space in much of the state
Salt spray affects coastal plantings
Rocky glacial soils need clearing
Growing sour orange here specifically
Sour Orange needs pH 5.5–8.3; Rhode Island's dominant fine sandy loam soils may or may not deliver that, so your parcel's SSURGO map unit is the real test.
Start with a soil test on your own ground and adjust pH and texture to fit sour orange's 5.5–8.3 range. How to handle it →
What to actually do about these — and the constraints that apply to every Rhode Island grower, not just sour orange — is covered on the Rhode Island growing guide.
Timing shifts within Rhode Island
Sour Orange needs about 140 days of frost-free season to complete its cycle. Even Providence County — Rhode Island’s shortest season at 210 frost-free days — clears that by 70 days, so season length isn’t the constraint anywhere in Rhode Island. What varies is your own parcel.
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"). Sour Orange's 140-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
Sour Orange draws honeybees (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, sour orange can only work that bloom inside Rhode Island's frost window — roughly 225 days, opening after the last 28°F freeze (Mar 27 - Apr 3) and closing at the first (Nov 7 - Nov 21), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant Sour Orange
Sour Orange is listed as toxic to dogs, cats (leaves, stems, peel) at a mild level (ASPCA). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear.
Rhode Island Cooperative Extension
For Rhode Island-specific cultivar recommendations, planting calendars, and pest pressure for sour orange, the canonical source is URI Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Sour Orange native to Rhode Island?
No — the USDA PLANTS Database lists Sour Orange as introduced rather than native in the Lower 48, so it is not part of Rhode Island's native flora. It grows here as a garden plant; pairing it with a few Rhode Island natives keeps local pollinators fed too.
Looking for plants that belong here? The Rhode Island 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 Sour Orange in Rhode Island
When can I plant Sour Orange in Rhode Island?
Rhode Island's last spring hard freeze (28°F) clears between Mar 27 and Apr 3, and the first fall hard freeze lands between Nov 7 and Nov 21 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Sour Orange, so this page does not state whether it overwinters in Rhode Island 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 Sour Orange grown in across Rhode Island?
Rhode Island spans USDA hardiness zones 6b-7b (USDA ARS PHZM 2023). Sour Orange 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 Rhode Island site have?
A typical Rhode Island site sees ~225 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Sour Orange needs 140+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Sour Orange native to Rhode Island?
No — the USDA PLANTS Database lists Sour Orange as introduced rather than native in the Lower 48, so it is not part of Rhode Island's native flora. It grows here as a garden plant; pairing it with a few Rhode Island natives keeps local pollinators fed too.
How should I amend the soil for Sour Orange in Rhode Island?
Sour Orange prefers pH 5.5-8.3 and well (dry spells) drainage (FAO ECOCROP). That sits in the common-ground band across Rhode Island soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Sour Orange actually grow on my specific land in Rhode Island?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores sour orange 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 Rhode Island
State-level data is a sketch. Your Growable Ground report scores sour orange against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Rhode Island sour orange averages can't show:
We read public map data around Rhode Island — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rhode Island sour orange average
Explore More
Growing guides for sour orange
Explore Rhode Island county by county
Rhode Island carries 5 counties with their own USDA zone — a sample of the growing pages for sour orange there:
Where else sour orange grows
Sour Orange's zone band crosses state lines — these are the states closest to Rhode Island 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 Rhode Island
Rhode Island has a growing page for 889 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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