Onion
Allium cepa
About it
- Kind
- Vegetables · Annual
- Family
- Amaryllidaceae
- Hardiness zones
- Zones 3–10
- Frost
- Hardy — takes a hard frost
- Sun
- Full sun
- Spacing
- 4 in apart, rows 12 in
- Soil depth in a pot
- At least 8 in
- Soil pH
- 6–7
- Water
- About every 4 days
When to plant
- Start indoors
- 10 weeks before planting out
- Plant out
- Plant out 4 weeks before the last frost
- Sow outdoors
- Sow 4 weeks before the last frost
- Soil temperature
- Germinates from 35°F
- Ready
- About 100 days from sowing
Based on your last frost date. Outside the US, check local advice.
Varieties people grow
- Candy— sweet onion that suits most of the country
- Patterson— long-day storage onion for the north; keeps long
- Red Burgundy— short-day red slicer for the south; use it fresh
- Walla Walla— long-day sweet onion for the north; poor keeper
- Yellow Sweet Spanish— large mild long-day onion for the north
Planting partners
What has been claimed about growing Onion near other plants, grouped by how well it has been tested. Most companion planting advice has never been tested; the notes say which is which.
Tested in field trials
- With Broccoli Onions planted with broccoli reduced cabbage looper and imported cabbageworm damage in an Iowa study. UMN Extension ↗
- With Cabbage Onions planted with cabbage reduced cabbage loopers and imported cabbageworms. UMN Extension ↗
Safety for pets and children
- Cats Listed as a problem for cats (NC State Extension) — Low severity; toxic principle: N-propyl disulfide
- Dogs Listed as a problem for dogs (NC State Extension) — Low severity; toxic principle: N-propyl disulfide
- Horses Listed as a problem for horses (NC State Extension) — Low severity; toxic principle: N-propyl disulfide
- Children No information in our sources
If a pet or child eats part of this plant, call your vet or poison control.
Read from NC State Extension ↗.
"No information" means our sources do not say, not that the plant is harmless. A non-toxic listing is not a reason to let anyone eat a plant.
Pests and diseases
Onion bulb rots Disease
What you'll see. Fusarium basal rot, Botrytis neck rot and bacterial soft rot can rot the bulbs in the ground or in storage.
What helps. Choose varieties resistant to Fusarium basal rot, and harvest on dry, cool days to limit rot after harvest.
Source: UMN Extension ↗
Check the label and your local extension service before using any product.
Where this comes from
- direct sow weeks rel last frost cmg.extension.colostate.edu ↗ CSU #720 (Colorado) hardy class, a class-wide figure: as early as 2-4 weeks before the last frost; Table 1 lists dry onions from seed and from sets with no transplant age
- family npgsweb.ars-grin.gov ↗ GRIN page: Allium cepa L.
- frost hardiness cmg.extension.colostate.edu ↗ CSU #720 (Colorado) hardy class lists onions
- maturity counted from cmg.extension.colostate.edu ↗ Row's 100 days (UMN) is inside NC State (North Carolina) Table 16-4's bulb S=90-120; CSU #720 (Colorado) dry onion 110 from seed or sets, unmarked
- maturity counted from NC State Extension ↗ Row's 100 days (UMN) is inside NC State (North Carolina) Table 16-4's bulb S=90-120; CSU #720 (Colorado) dry onion 110 from seed or sets, unmarked
- min soil temp f cmg.extension.colostate.edu ↗ CSU #720 (Colorado) Table 1: dry onion germination minimum 35°F
- Most facts UMN Extension ↗ Backfilled by 0041. Pre-0041 rows recorded one source for the whole row; per-field attribution was never captured and is not invented here.
- toxicity NC State Extension ↗ toxic for cat, dog, horse from the page's "Problem for" listing. Severity, parts and principle are the page's poison characteristics for the whole plant. Page matched to this row by its recorded species; not cited by the row before this batch.
- transplant weeks rel last frost extension.unh.edu ↗ UNH (New Hampshire) table: onion transplants 4 weeks before last frost