Planting timing · Frost-anchored
When to plant onions
When to plant onions here is cited sets, seed, transplant, and day-length context — not a national calendar month. Day-length notes are explained from the sheets, not sold as a catalog. There is no single trick.
Growing guidance is general information. Timing, spacing, and care depend on cultivar, weather, soil, and local conditions. Check the sources and adjust the plan for your garden.
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Use your last-spring-frost history — not a national month.
A ZIP calculator is not live on this page. Save the bed to store the window you actually used.
Sets, seed, and transplant notes are source-specific — not a national month.
Types live on the onions hub. Spacing, water, and cited harvest/cure comparison live on onion plant care.
Cited sets, seed, and transplant timing (not a national date)
Separate source assertions — not a BioArva average.
- Clemson HGIC 1314 (South Carolina): onions are grown from seed, sets, or transplants; plant seed for bulb onions in the early fall; onion sets can be planted in fall or early spring; onions grown from transplants should be planted in the early spring. Timing on their sheet — not a BioArva calendar.
- Maryland Extension (Maryland): their sheet lists planting onions in early spring once the garden can be cultivated, and notes cold exposure in the context of seed-stalk development. Timing context on their sheet—not a BioArva calendar or diagnosis.
- Maryland Extension (Maryland): their sheet lists spring planting for onion sets. Timing context on their sheet—not a BioArva how-to.
- Maryland Extension (Maryland): either buy bunches of onion transplants or start your own by sowing seeds indoors about 8 weeks prior to planting. Transplant timing on their sheet — not a BioArva how-to.
- Illinois Extension (Illinois): onions can be planted as soon as the garden can be tilled in the spring. Timing on their sheet — not a BioArva calendar.
- UMN Extension (Minnesota): you can grow onions from seed, transplants or small bulbs called sets. Starting-stock note on their sheet — not a ranking.
- Utah State (Utah): plant onion seeds ¼–½ inch deep in late March or early April. Timing on their sheet — not a BioArva calendar.
- Clemson HGIC 1314 (South Carolina): their sheet distinguishes sets over one inch. Set-size context on their sheet — not a BioArva standard or diagnosis.
- Maryland Extension (Maryland): onions are hardy (can withstand heavy spring frosts). Hardiness on their sheet — not a BioArva climate zone.
- Clemson HGIC 1314 (South Carolina): onions grow best during cool weather and are usually planted in the fall in South Carolina for late spring harvest; onion plants can also be planted in early spring for summer harvest. Timing on their sheet — not a BioArva calendar.
- Clemson HGIC 1314 (South Carolina): their sheet lists onion-set windows of Feb 15 to Mar 30 (Piedmont spring) and Sept 15 to Oct 15 (Piedmont fall); Coastal spring Feb 1 to Mar 15 and fall Sept 15 to Nov 15. Timing on their sheet — not a BioArva calendar.
- Clemson HGIC 1314 (South Carolina): plant onion seed directly in the garden in fall in Coastal and Central areas; seed is not a recommended method for growing onions in the Piedmont area of South Carolina. Timing on their sheet — not a BioArva how-to.
- Clemson HGIC 1314 (South Carolina): set out transplants from late December through February; plants should be about 6 inches high and about half the thickness of a lead pencil at transplanting. Timing/size on their sheet — not a BioArva how-to.
- UMN Extension (Minnesota): direct seed as soon as the soil is workable in the spring. Timing on their sheet — not a BioArva calendar.
- UMN Extension (Minnesota): onion transplants can tolerate light frosts, and you can plant them when temperatures reach 50°F. Timing on their sheet — not a BioArva calendar.
- UMN Extension (Minnesota): you can raise your own transplants by starting seed indoors 10 to 12 weeks before planting outside. Indoor-start interval on their sheet — not a BioArva how-to.
- Illinois Extension (Illinois): onions can be planted as soon as the garden can be tilled in the spring, usually late March or early April in prime regions for producing onions. Timing on their sheet — not a BioArva calendar.
- Utah State (Utah): their sheet lists planting onion seeds in mid to late August for overwintering, with mulch late in the year for overwintered special varieties. Timing on their sheet — not a BioArva calendar or winter-protection promise.
- Maryland Extension (Maryland): sets are planted with the pointed end up and covered with 1 inch of soil. Planting-stock note on their sheet — not a BioArva how-to.
- Clemson HGIC 1314 (South Carolina): sets should be planted 1½ inches deep and seeds ½ inch deep. Planting-stock depth on their sheet — not a BioArva how-to.
- Clemson HGIC 1314 (South Carolina): set plants with the bottom of the plant about 1 to 1½ inches below the surface of the soil. Transplant depth on their sheet — not a BioArva how-to.
- Clemson HGIC 1314 (South Carolina): sow eight to 12 seeds per foot of row ½ to ¾ inches deep. Seed-depth on their sheet — not a BioArva how-to.
- Clemson HGIC 1314 (South Carolina): their sheet lists onion-plant windows of Sept 15 to Oct 15 (Piedmont) and Oct 1 to Nov 15 (Coastal). Timing on their sheet — not a BioArva calendar.
- Clemson HGIC 1314 (South Carolina): their sheet lists onion-seed windows of Sept 15 to Oct 30 in Coastal areas. Timing on their sheet — not a BioArva calendar.
- Illinois Extension (Illinois): to produce dry onions, plant the smaller sets 1 inch deep. Set-depth on their sheet — not a BioArva how-to.
- Utah State (Utah): their sheet lists April planting for transplants or sets. Timing on their sheet — not a BioArva calendar.
- Utah State (Utah): transplants require about 8 weeks of grow time before planting in the garden. Indoor-start interval on their sheet — not a BioArva how-to.
- Maryland Extension (Maryland): sow seed ¼ inch to a ½ inch deep and cover lightly with fine soil. Seed-depth on their sheet — not a BioArva how-to.
- UMN Extension (Minnesota): sow seeds in a 2-inch wide band, 1/4 to 1/2 inch deep, in rows 12 to 18 inches apart. Seed-depth on their sheet — not a BioArva how-to.
Cited day-length context (explained, not a catalog)
Separate source assertions — not a BioArva average.
- Clemson HGIC 1314 (South Carolina): short day varieties set bulbs with about 12 hours of daylight and are suitable for growing throughout South Carolina; long day onions cannot be successfully grown in the South. Day-length on their sheet — not a BioArva climate zone.
- Maryland Extension (Maryland): if the seed catalog lists the variety as long day, it sets bulbs when it receives 15–16 hours of daylight and is adapted to Northern summers; short-day varieties set bulbs with about 12 hours of daylight and are used in the deep South for winter production; there are also intermediate cultivars. Day-length on their sheet — not a BioArva climate zone.
- UMN Extension (Minnesota): storage onions grown in Minnesota generally are long-day types that require 14 or more hours of daylight to form bulbs. Day-length on their sheet — not a BioArva climate zone.
- UMN Extension (Minnesota): their sheet lists sweet or mild onions as short-day types in Minnesota. Day-length on their sheet — not a ranking or size claim.
- Illinois Extension (Illinois): most common varieties fall into long-day (for northern latitudes) and short-day (for southern latitudes); onion varieties grown in the South are not adaptable to the North and vice versa. Day-length on their sheet — not a BioArva climate zone.
- Utah State (Utah): their sheet lists onion bulbing under long days and hot weather, and notes late-spring planting in the context of leaf growth versus bulb formation. Timing context on their sheet — not a BioArva diagnosis.
What month can you plant onions?
This guide does not name a US month. Maryland Extension (Maryland): their sheet lists planting onions in early spring once the garden can be cultivated. Timing context on their sheet—not a BioArva calendar or diagnosis.
What is the trick to growing onions?
There is no single trick. UMN Extension (Minnesota): you can grow onions from seed, transplants or small bulbs called sets. Starting-stock note on their sheet — not a ranking.
What are common onion growing mistakes?
This guide does not diagnose mistakes. Maryland Extension (Maryland): their sheet notes cold exposure in the context of seed-stalk development. Timing context on their sheet—not a BioArva calendar or diagnosis.
How long does it take for onions to grow?
This guide does not state days-to-maturity.
Is April too late to sow onion seeds?
This guide does not set an April cutoff. Utah State (Utah): plant onion seeds ¼–½ inch deep in late March or early April. Timing on their sheet — not a BioArva calendar.
Do onions come back every year if you plant them?
This guide does not state that onions return every year.
What not to plant next to onions?
This guide does not provide companion-planting guidance.
What to record in the Field Book
Save the bed with the crop and the date. You may add a photo and notes. Compare entries you have recorded with each other — not with a diagnosis from this page. If you want an identification, bring the record to local Extension.
How we know — methodology. Ranges and assertions are cited per source, not blended.