Vegetable / Cool season
Onion
Pick the right day length or grow tiny bulbs
Plant out byApr 6zone 6
- Family
- Onion (Amaryllidaceae)
- Sun
- Full sun (6+ h)
- Difficulty
- Some care
- Days to harvest
- 70-120 days
- Spacing
- 4 in apart, rows 12 in
- Pot size
- 3 gal pot (fine in pots)
- Frost
- Hardy
- Start
- Either
- Water
When to plant
Showing .
Averages for a typical garden in the region. Your local frost dates may differ by 2-3 weeks, check a local source.Wait until Feb 9
In zone 6, start seeds indoors Feb 9 to Feb 23; plant out Mar 23 to Apr 6. Average last frost Apr 20, first fall frost Oct 20.
Units
Onions read the calendar by daylight. A bulb only starts to swell once days reach a set length, so a variety bred for Texas will stall in Minnesota, and the other way round. Short-day types fit the South, long-day types fit the North, and intermediate or day-neutral types cover the middle. Buying the wrong one is the classic mistake, and it gives you tall leaves on top of small bulbs.
Sets are the easy road. Push the little bulbs in, pointy end up, about 2 to 4 weeks before your last spring frost and 3 to 4 inches apart. Bury them 1 to 2 inches deep, no deeper. Seeds take longer. Start them indoors 8 to 10 weeks before the last frost and plant out when the stems are about as thick as a pencil. Cold doesn't bother them much. Hot, dry spells are what push a plant to send up a flower stalk, and a bolted onion won't keep, so eat that one first.
Weeds are the daily fight. Onion leaves are thin and cast almost no shade, so grass moves in fast. A short hoe pulled along the row once a week saves a lot of hand weeding. They grow fine in a planter but stay modest, more of a handful than a winter supply. In mid to late summer the tops yellow and flop over. Let the necks dry down, then pull them on a dry day.
Things to consider
- Onion maggots get worse in long wet spells. A row cover laid over new plantings keeps the flies from laying eggs at the base of the plants, where the maggots tunnel into the bulbs.
- Crowded rows and soggy ground invite white rot and other fungal trouble. Rotate the patch each year and clear old leaves and culls at season's end, since the fungi live on in that debris.
- Tall crops that shade the row will shrink your bulbs. Put onions on the sunny edge of the bed, in front of anything tall, so they get the full day of light they need.
Good neighbours
Keep apart
Pests to watch for
Onion thripsOnion maggots
Questions about growing onion
Sets, seeds or transplants: which should I buy?
Sets are the simplest and most forgiving choice, and they go in early. Seeds cost less and come in many more varieties, but they need a long indoor start under lights. Bundles of young transplants sit in between, and they are a handy way to get a named day-length type without the indoor work.
How do I cure onions for storage?
Spread them out in one layer in a dry, shaded, airy spot until the necks are papery and the skins rustle, then trim the tops and roots. Keep any with thick, damp necks for the kitchen, because those tend to rot in storage. Well-cured onions keep for months in a cool, dry place with good airflow.
How do I find my day-length type?
A rough rule is short-day in the southern US and long-day in the northern US. Near the middle, intermediate or day-neutral types are the safe pick, and they forgive a guess. Your local extension office or a good garden center can name varieties that do well near you.
Save this crop
Pin it to a garden board so it is there when planting time comes round.
Similar crops
Sources
General guidance for home gardens. Frost dates are averages for a zone or region; check a local source (in the US your county extension office) for local timing.