Yes — Strong Match
ammi is grown as an annual, so season length decides it here, not a winter zone — and Rhode Island's typical season runs ~225 frost-free days against the ~60 ammi needs.
Sow by about Aug 16
Ammi is grown as an annual, so what decides it here is season length, not a winter zone. It needs about 60 frost-free days and a typical Rhode Island season runs ~225 frost-free days, leaving 165 days of slack. That is room to sow as late as about Aug 16 and still finish before the usual first freeze (Nov 14), or to run a second succession.
Want more weeks at either end of that window? How to buy the weeks →
60 frost-free days required against Rhode Island’s ~225-day season. NOAA Regional Climate Centers ACIS 1991-2020 (28°F killing freeze), state median across counties, via stateClimateData.ts.
Your yard isn't the whole zone.
Ammi is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Rhode Island site runs ~225 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score ammi against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Zone Comparison
Ammi Needs
- USDA Zones: Data pending
- Frost-Free Days: 60+
- Sun: Full Sun
- Mature size: 3.5 ft tall
- Picking window: ~60 days of harvest
- Drought tolerance: Low
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
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 Ammi 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.
When to start the seed
Ammi is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Rhode Island's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 90 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 128 days to spare even in Rhode Island's tightest freeze scenario — room for a later start or a second sowing.
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
Frost-free days
Ammi wants 60+ frost-free days; a typical Rhode Island site sees ~225 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Ammi needs ~1000 GDD (base 50°F) to ripen. The state median runs ~2635 GDD (from PRISM 1991-2020 climate normals), so Rhode Island's typical season clears that easily.
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
Ammi likes near-neutral soil (pH 6-7). That's the common-ground band across Rhode Island's glacial till and sandy loam — a soil test confirms it for your site. 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. What matters for ammi is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how ammi performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Rhode Island soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Ammi in Rhode Island — Quick Answer
- Verdict: Yes — Strong Match
- Plant Zones: Data pending (USDA PLANTS Database)
- State Zones: 6b-7b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 27 - Apr 3 to Nov 7 - Nov 21 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 90 days
What Else to Consider for Ammi 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 ammi here specifically
Rhode Island's soils run mostly fine sandy loam (Inceptisols), and whether that suits ammi's pH 6.0–7.0 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward ammi's 6.0–7.0 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Rhode Island grower, not just ammi — is covered on the Rhode Island growing guide.
Timing shifts within Rhode Island
Ammi needs about 60 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 150 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"). Ammi's 60-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
Ammi draws honeybees, native bees, and butterflies (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, ammi 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 Ammi
Ammi 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 Rhode Island this is a one-season plant and the first hard freeze (Nov 7 - Nov 21) takes it down, so the exposure above is a summer-long one rather than something standing in the bed all year.
Recommended Ammi Varieties for Rhode Island
Rhode Island publishes no state variety trial for ammi, so we won't invent a "best for Rhode Island" list. Choose types rated to your USDA hardiness zone (6b-7b), and confirm winter survival and drainage against your own parcel.
Rhode Island Cooperative Extension
For Rhode Island-specific cultivar recommendations, planting calendars, and pest pressure for ammi, the canonical source is URI Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Ammi native to Rhode Island?
No — the USDA PLANTS Database lists Ammi 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 Ammi in Rhode Island
When can I plant Ammi 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). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
Can Ammi mature before first frost in Rhode Island?
Yes — Ammi matures in 90 days (USDA PLANTS Database), and Rhode Island's dependable hard-freeze-free window runs 218 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 128 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Ammi grown in across Rhode Island?
Rhode Island spans USDA hardiness zones 6b-7b (USDA ARS PHZM 2023). Ammi carries a range of zones Data pending, 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). Ammi needs 60+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Ammi native to Rhode Island?
No — the USDA PLANTS Database lists Ammi 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 Ammi in Rhode Island?
Ammi prefers pH 6-7 and well (dry spells) drainage (Growable Ground Plant Database). 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 Ammi actually grow on my specific land in Rhode Island?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores ammi 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 ammi against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Rhode Island ammi 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 ammi average
Explore More
Growing guides for ammi
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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