Onion
Allium cepa
A vegetable, planted March to May, or sown January to April.
In September: dry the onion off for storing and lift the crop.
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Onion, month by month
Bar: the usual months. Sprout: this month.
| Sowing, planting or job | Sep | Oct | Nov | Dec | 2027Jan | Feb | Mar | Apr | May | Jun | Jul | Aug |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow under cover. | none | none | none | none | usual | usual | usual | none | none | none | none | none |
| Sow outdoors. | none | none | none | none | none | none | usual | usual | none | none | none | none |
| Plant out. | none | none | none | none | none | none | usual | usual | usual | none | none | none |
| Plant onion sets. | none | none | none | none | none | none | usual | usual | none | none | none | none |
| Net the onion. | none | none | none | none | none | none | usual | usual | none | none | none | none |
| Dry the onion off for storing. | usual | usual | none | none | none | none | none | none | none | usual | usual | usual |
| Cut the flower stems off the onion. | none | none | none | none | none | none | none | none | none | none | usual | none |
| Lift the onions. | usual | usual | none | none | none | none | none | none | none | none | usual | usual |
What to do, and when
The usual months for a UK garden. Your own plan gives the week.
Sowing and planting
Sow under cover January to March, 1.3cm deep. Strong source: RHS.
Sow outdoors March to April, 1.3cm deep, 10cm apart, rows 20 to 30cm apart. Strong source: RHS.
Plant out March to May, 10 to 15cm apart, rows 25 to 30cm apart. Strong source: RHS.
Plant onion sets March to April, 2cm deep, 10 to 15cm apart, rows 20 to 30cm apart. Strong source: RHS.
Net the onion
Birds peck newly planted sets out of the ground, so keep them covered until they root.
Usually March to April. Strong source: RHS.
Dry the onion off for storing
Gardeners call this curing and ripening off for storage.
Dry them for about two weeks in full sun on wire racks, so air can circulate beneath.
Usually June to October. Strong source: RHS.
Cut the flower stems off the onion
Gardeners call this flower-stem and scape removal.
Remove them as soon as they start to form, so the plant’s energy goes into swelling the bulb. From RHS.
Usually July. Moderate source: Suttons.
Lift the onions
Usually July to October. Strong source: RHS.
What the source words mean
Strong: the RHS page for this plant is among them.Moderate: another trusted UK source, or the RHS on its group.
What not to do
Don’t bend the onion tops over
Bending the tops over to ripen the bulbs is no longer recommended. The leaves yellow and topple on their own as the crop matures.
June to October. Strong source: RHS.
Every line above names the page it comes from. Where we found no good source for a job, we left it out. Where the name “Onion” comes from.