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From what I've read there seem to be two ways to plant onions - either put part of an onion in the ground, or leave one in the ground for two years and then plant the seed from the resulting flower. But I've also read that there is some system where something is planted once, harvested, and then replanted. What would be the point of that?

Since all of this looks counter intuitive to me, I was wondering if I understood correctly, and if so, what is the point of harvesting and then replanting?

(I was also wondering what would be the benefit (for the vegetable) of a vegetable growing a flower only in its second year. But that might warrant a separate question.)

  • Onions (and other vegetable crops) don't always flower in the second year. If growing conditions are bad, they often flower and die in the first year, without producing the parts of the plant that humans want to eat. – alephzero Oct 8 at 11:36
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To come straight to an answer which may be of relevance to you, consider that the onion family has become adapted to a wide variety of growing environments. One member of that family is the Egyptian, Tree or Walking onion which develops clusters of small bulbils at the end of the flowering stalk. These become heavy, flop over and take root at a small distance from the mother plant. So a cultivator can take advantage of this behaviour by removing a mature set of bulbils, separating them to individuals and planting each one favourably to produce a single large bulb. Since they are in this sense perennial, this fits your description of plant, harvest, plant, never actually going through a seed/seedling stage.

More generally onions are biennials which from seed build a store of resources in the first year, which is followed in the second year by the flowering and seeding stage. Since it can take some time to build the required resources the plants have adapted to taking one full season for the first stage, implementing a shut down to survive the winter or rest period and then reawaken to produce the reproductive behaviour. In some seasons the trigger to move to reproduction can happen early, particularly when the plant is under stress, perhaps due to drought or unusually long spells of sunshine.

Since the onion family is adept at adaptation, there is also the planting of setts, or onions grown from seed to a small size and then artificially forced into early maturity. These are then planted the following spring and allowed to complete their normal first year activity by expanding the small bulb to a large store of resources that is useful as food.

  • and then artificially forced into early maturity - What does that mean? Do you mean that it's harvested because there is not enough time in the season to grow enough? – ispiro Oct 8 at 12:17
  • No, the onions are grown from seed, but started late in the season so they only have time to produce little bulbs, quite useless as storage onions, but which when planted the following spring will continue growing to large bulbs. – Colin Beckingham Oct 8 at 12:26
  • So why not start early in the season and do it all in one go? Is it because these seeds are only ripe late in the season? – ispiro Oct 8 at 12:43
  • The idea is that onions from seed can be more troublesome: non-germination, vulnerable to disease, irregular appearance and so on. By buying setts you are buying more bulk, but bypassing the inconvenience of seeding/transplanting at a busy time of year. Also the setts method tends to produce larger bulbs at the end of the true growing season than might have come from seed. The downside is that bulbs from setts can result in double bulbs (two separate bulbs tightly connected) which is a disadvantage if you are looking for perfect onion rings when slicing in the kitchen. – Colin Beckingham Oct 8 at 13:11
  • @ispiro Also, some varieties are F1 hybrids, which will not breed true if you save your own seeds. So given the choice between buying seeds and setts for those varieties, setts are more reliable and less trouble. – alephzero Oct 9 at 11:58

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