Generally — Most Areas
onion (zones 2-11) suits most of Hawaii (8b-13a) — zones 8-11 are in range, and the rest of the state is the exception.
Onion in Hawaii — the short answer
Onion in Hawaii: hardy in zones 2–11, full sun, against a state median of ~365 frost-free days.
- Plant zones
- 2-11
- 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
- Hawaii zones
- 8b-13a
- USDA PHZM 2023
- Killing freeze
- None on record
- NOAA RCC ACIS 1991-2020
- Shortest county season
- 365 days
- NOAA Regional Climate Centers ACIS station record, 1991-2020, county 28°F killing freeze
- Days to maturity
- 110 days
- Growable Ground Plant Database
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.
Hawaii spans zones 8b-13a, 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 onion against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Onion Needs
- USDA Zones: 2-11
- Frost-Free Days: 85+
- Sun: Full Sun
- Mature size: 1.5 ft tall
- Picking window: ~7 days of harvest
- Drought tolerance: Medium
Hawaii Has
- USDA Zones: 8b-13a
- Hard Freeze (28°F): None on record — year-round season
- Annual Rainfall: 10-400 inches
- Common Soils: Volcanic, Laterite, Coral sand
Plant Zone Range (zones 2-11)
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 Onion in Hawaii
The frost window
Hawaii has none — the 1991-2020 station record carries no 28°F killing freeze, so there is no last-frost date to plant after and no first-frost date to harvest before (NOAA Regional Climate Centers ACIS station record). The growing season is year-round; what paces planting here is rainfall, heat and elevation, not the calendar.
Establishment timing
As a long-lived plant, onion can go in any month here. Aim for the start of your wetter season so it establishes on rainfall rather than on irrigation, and give it a year in the ground before judging it.
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 onion survives winter in part of Hawaii, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Onion wants 85+ frost-free days; a typical Hawaii site sees ~365 (NOAA Regional Climate Centers ACIS station record, 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 station record, 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
Onion tolerates a wide pH range (pH 4.3-8.3) — 4 units, acid ground through alkaline — so soil acidity is rarely what limits it in Hawaii. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a Hawaii soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Hawaii site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
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. Hawaii soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant onion 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 onion goes in. What follows is Hawaii’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 Hawaii — and how to grow with it.
We checked the federal record across Hawaii — 4,542 documented sites across 7 of the 9 source types we track.
The most significant on record: 86 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Hawaii 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.
Severity Distribution
across Hawaii
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Hawaii, two things run higher than the national average across Hawaii — Superfund (86 sites) and PFAS (40 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.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What Else to Consider for Onion in Hawaii
Zone compatibility tells you about winter cold survival — but Hawaii growers also need to think about:
Extreme rainfall variation — desert on one side, rainforest on the other
Volcanic soil is nutrient-poor in young flows
Invasive species pressure is severe
What to actually do about these — and the constraints that apply to every Hawaii grower, not just onion — is covered on the Hawaii growing guide.
Timing shifts within Hawaii
Onion needs about 85 days of frost-free season to complete its cycle. Even Hawaii County — Hawaii’s shortest season at 365 frost-free days — clears that by 280 days, so season length isn’t the constraint anywhere in Hawaii. 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"). Onion's 85-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
Onion draws honeybees, native bees, and butterflies (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Onion's flowers are not fenced in by a freeze date here: the 1991-2020 record resolves no 28°F killing frost anywhere in Hawaii, so what limits bloom is the plant's own cycle rather than the calendar.
Hawaii Cooperative Extension
For Hawaii-specific cultivar recommendations, planting calendars, and pest pressure for onion, the canonical source is UH Mānoa CTAHR Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Onion native to Hawaii?
No — the USDA PLANTS Database lists Onion as introduced rather than native in the Lower 48, so it is not part of Hawaii's native flora. It grows here as a garden plant; pairing it with a few Hawaii natives keeps local pollinators fed too.
Looking for plants that belong here? The Hawaii 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 Onion in Hawaii
When can I plant Onion in Hawaii?
Any month — Hawaii records no 28°F killing freeze in the 1991-2020 station record, so there is no last-frost date to wait for and the growing season is year-round (NOAA Regional Climate Centers ACIS station record). Pace planting by rainfall, heat and elevation instead: the summit country does freeze, and no station up there carries a long enough record to date it.
What hardiness zone is Onion grown in across Hawaii?
Hawaii spans USDA hardiness zones 8b-13a (USDA ARS PHZM 2023). Onion carries a range of zones 2-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Hawaii site have?
A typical Hawaii site sees ~365 frost-free days per year (derived from NOAA Regional Climate Centers ACIS station record, 1991-2020). Onion needs 85+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Onion native to Hawaii?
No — the USDA PLANTS Database lists Onion as introduced rather than native in the Lower 48, so it is not part of Hawaii's native flora. It grows here as a garden plant; pairing it with a few Hawaii natives keeps local pollinators fed too.
How should I amend the soil for Onion in Hawaii?
Onion tolerates pH 4.3-8.3 and well (dry spells) drainage (FAO ECOCROP). That is a 4-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Hawaii site — amend for drainage and organic matter first.
Will Onion actually grow on my specific land in Hawaii?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores onion 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 Hawaii
State-level data is a sketch. Your Growable Ground report scores onion against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Hawaii onion averages can't show:
We read public map data around Hawaii — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Hawaii onion average
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Growing guides for onion
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