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Onion and Salad Onion

Allium cepa

Harvest time for some onions by 12th July – we shall transplant the whole bed within two weeks, with chicory for radicchios; a summer planting of chard is on the right

Allium cepa is best known for the bulb onions, so widely used in almost all cultures and cuisines. This lesson is about growing them, and also their subtype, spring or salad onion, or scallion, used at an immature stage before they bulb.

Shallots are Allium ceps var. aggregatum, formerly called ascalonicum, from their origins in Ashkalon in Canaan. Shallots are closely related to onions and smaller in size. They have a softer cell structure, meaning they soften more readily when sautéed.

As with lettuce, this lesson is a visual feast for you, with so many of my photos from the last 14 years. Why 14? In 2006, I bought a digital camera!

An early August view across onions, marigolds, beetroot and summer lettuce
Red Baron onions in early August – sets planted in late April, with interplants of chicory and beetroot
At an RHS Show in October – exhibition onions can be quite large; these are the classic Kelsey, sown in late December – Mr Mace won only the second prize; also notice some lovely shallots, bottom left

I am not discussing perennial onions (Allium fistulosum) here, known colloquially as Welsh onion, Japanese bunching onion and many other names. Those plants do not make bulbs and keep growing new stems, a good way to have regular supplies of green onion.

  • Seeds of Japanese bunching onion, such as the variety Ishikura, are sold as an alternative to Allium cepa salad onions. The selling point is that fistula onions do not bulb and make longer stems.
  • Against that, I find them more prone to mildew – see ‘Diseases’ below.
30th April – module-sown onion and directly sown carrots, plus radish, after four to six weeks of fleece cover
6th June – the same onions and carrots, with some self-sown Escholzia flowers
Longor shallot, multisown with four seeds – this is mid-June, three months after transplanting

Harvest period

  • Days from seed to first harvest: for bulbs 140–160, overwintered 260
  • Days from seed to first harvest: for salad onions 80–100, overwintered 190–240

Best climate is warm summers, continental or temperate, not too humid.

Why grow them

My customers, and friends helping in the kitchen to prepare food, remark on how my onions make them cry so much!

Why does chopping an onion make us cry? They release a substance, syn-propanethial-S-oxide, which irritates the eyes’ tear glands. Perhaps from high levels of sulphur, which is healthy.

  • Most onions of commerce are grown with synthetic fertilisers which increase the water content, probably without a corresponding increase of micronutrients. They are therefore agreeably mild, with less flavour and pungency.
  • Onions of all kinds have many health benefits, such as the vitamin C in raw onion, and chromium, which helps regulate blood sugars.
  • With traditional digging and the wide spacing normally recommended, onions involve a lot of weeding and work per amount of harvest.
  • With no dig and closer spacing, onions are easy to grow and harvests are so good!

I am diabetic type 1 and eat a lot of onion – it’s almost my staple vegetable ahead of potatoes. As a treat, I love them roasted, which heightens the sweetness.

No dig on the left and dig on the right – an onion comparison from the trial beds at Lower Farm in 2009
Dig bed shallots on the left, with no dig on the right – August 2016
25th July – side view of the onion harvest and second plantings in my dig and no dig bed trial; the dig bed, further away, gave 10.8 kg/23.8 lb of onions after drying tops, and the no dig gave 12.3 kg/27 lb, from two rows across each 1.5 m bed
28th May 2012 – the no dig bed with onions transplanted in March, and with compost on the surface
28th May 2012 – the dig bed with onions transplanted in March, and with compost dug in
26th July – the onion harvest of both beds; once dry there were 6.64 kg/14.6 lb from the dig bed and 7.25 kg/16 lb from the no dig bed, with the same bed area and plant numbers

Pattern of growth

Onions are hardy annual and biennial. For food, we grow them for their first-year stage of stems and bulbs. They overwinter as bulbs, then grow again and flower in the second summer. Or we can overwinter them as seedlings, to harvest in the following spring and summer.

Salad onions are bred to grow long, whiter stems, while others are bred to swell more at the base. There is a fine line between these two categories, a quality difference. Best results are from respecting the varietal descriptions, but it’s possible to grow salad onions for bulbs, and bulb onions for eating green – see the variety Lilia below.

  • Leaf growth is healthiest through spring, especially late spring (May) when leaves suddenly grow tall and strong.
  • They lose vigour by the summer solstice, when bulbs start to swell noticeably.

By late summer and autumn, green leaves are less healthy because they are out of season. Meanwhile, sow more onions in late summer, which overwinter as small seedlings with well-grown roots. They grow rapidly from early spring.

  • Autumn-sown bulb onions swell for an early harvest from late spring, but do not store as well as spring-sown bulb onions.
-5 °C/23 °F in January – a frost on White Lisbon spring onion, and beyond you can see Savoy cabbage
White Lisbon salad onions in February – these were multisown in late August
The White Lisbon patch gave hundreds of spring onions, and a few we did not pick have now grown into white bulb onions

Suitable for containers/shade?

The tidy leaves of onions make them ideal for containers. You will get the most value from growing the fistulosum types, for repeat harvest of green leaf and stem.

Be careful with growing onions in shade, because this may allow mildew to develop towards midsummer. They do grow in the shade, but are healthier and stronger in full sun.



Sturon is my go-to, for even growth and excellent storage.

Rose de Roscoff, ‘Keravel’, matures two weeks earlier than Sturon, is a beautiful pink colour and starts sprouting by late winter in storage.

Stuttgarter Giant is a great keeper, with a flat shape and strong flavour.

Hylander F1 and Santero F1 both resist mildew, are yellow and round, and store well.

11th July – see the varietal difference of onions maturing at different speeds; Rose de Roscoff at the front and Hylander at the back
29th July – Hylander onions are ready to pull at this stage, to dry in place or under cover
19th July – Romata do Milano; these would have been better thinned, as you can see some of the onions are long and thinner

Tropea Rossa Lunga is a long red onion, close to being a ‘banana shallot’. There is only a small difference between some onion and shallot varieties – it can be confusing.

Rosa Lunga di Firenze is even longer, thinner and more pink than red. Not for long storage.

Robelja red onion is a little paler than Red Baron, with a flatter shape and stores well.

Walla Walla grows a white bulb of mild and sweet flavour; it needs eating before it shoots in early winter.

Senshyu Yellow Express is an excellent Japanese bulb onion for sowing late summer, of fistulosum type.

Red Baron grows lovely firm onions that store well, with an intense dark colour.

Late July – Red Baron onions from seed, grown in clumps of three to four
15 days later – the same Red Baron onions drying in the greenhouse in a wet August
Robelj at the front and Sturon behind, during snow in January; these have been in the coldframe for five months so far


Zebrune F1 is a good shallot to grow from seed, with long brown to pink bulbs.

Golden Gourmet is a round, yellow shallot that stores well.

Longor are true to their name and have a lovely pink colour – see the photo above.

Eschalotte Grise or Griselle or Gray Shallot are all the French grey shallot, quite small and more long than round, and renowned for their top flavour.

Mid-July – mature multisown Zebrune shallot
Conservor shallot ready to be pulled in late July; these are from seed, with three seeds per clump
Two weeks later – Conservor shallots are now drying in the greenhouse


White Lisbon is my favourite, for its long white stem, dark green leaves and also a tasty white bulb when allowed to mature.

Apache grows lovely red-bottomed salad onions.

Lilia is called ‘dual-purpose’: 1) for lovely red salad onions, and 2) for bulbs in midsummer, although they are prone to bolting by solstice time.

28th March – Lilia spring onions, sown just under eight months ago; there’s too much soil in the surface compost which is causing it to crack
21st May – a harvest in late spring, including overwintered Lilia onions on the right
17th June in the Small Garden – 2.2 kg/4.8 lb of Lilia spring onion from thinnings, and there were 3.1 kg/6.8 lb of bulb onions in July

sow & propagate
Transplant - Size, time of year, Spacing, support
container growing
Prune and train plants/thin fruit
Harvest times and method
Potential problems


After removing bulbs from bed to shed, there may be a few weeds to pull, then rake lightly. You now have clear ground and are ready to plant again, perhaps after some watering if it has been dry.

  • You don’t need to apply any compost or amendments at this stage, wait until late autumn or winter, after the next planting has finished.

Follow with

After salad onions in spring, you can plant almost any vegetable. You may want to spread some compost, if none was applied in autumn, before transplanting the onions.

After bulb onions finish in summer, your choices depend a little on the exact timing of the space coming clear. They include, as transplants, not sowing direct:

  • Kale at close spacing, for medium leaves in autumn.
  • Multisown beetroot, for small to medium roots by late autumn.
  • Bulb fennel.
  • Celery for small heads by mid-autumn.
  • Salads such as endive, lettuce and radicchio.
  • Chinese cabbage and other brassicas, such as pak choi and salad rocket, but with no rush to transplant them – see Lesson 13, Course 3A. See also ‘Interplanting’ above.
6th August – multisown beetroot interplanted three weeks ago between Red Baron onions from sets
Atlantic F1 turnip in late October, sown in August straight after the onion harvest