How Do Onions Reproduce

Onions (Allium cepa) are biennials, that produce bulbs their first year. Onion bulbs store the nutrients that the onion flowers need for the producing seeds. When onions grow stems and flowers, it is known as bolting. When this happens, the stems produce seeds for onion reproduction.


Seed to Seed Reproduction

Reproducing onions using the seed-to-seed method is inexpensive and less work than planting bulbs. It also allows you to choose from a variety of cultivars for your specific needs. Once you plant the seeds in your garden, you just leave them there to grow into bulbs, bolt and then gather the seeds. Follow these tips for producing your own onion seeds:

  • Prepare your garden soil in late summer, removing all stones, weeds and clumps of soil.
  • Sow your onion seeds about one-half-inch deep and in rows that are two-feet apart.
  • Allow your seedlings to grow beyond their juvenile stage.
  • Vernalization will happen to the plants in the fall and winter. This cooling off period gets the onion plants ready for flowering in the spring.

Bulb to Seed Reproduction

If you have a favorite type of onion, and you want to maintain the purity of the onion, planting bulbs may be your best option. With bulb-to-seed reproduction, you plant mature onion bulbs. One requirement for planting bulbs for seed production is to vernalize the bulbs to encourage bolting. This occurs naturally in your garden in the fall, when the temperature falls below 50°F (10°C) for an extended period.

Onion bulbs become established in your garden much faster than seeds do. Plant the bulbs in well-drained soil about two-inches apart. Cover them with one inch of soil.

Pollination of Onions

Like other seed producing plants, onion flowers need pollination. The male and female parts of the onion flower develop at different times, making them ideal for cross pollination by insects. The umbel, or flower cluster lasts for about four weeks. Flies are the best pollinators of onions because honey bees aren’t attracted to the nectar.

Harvesting Onion Seeds

Determining when to harvest your seeds depends on the weather and seed maturation. Harvest your seeds when they’re black. About 10 percent of the seed should be visible in the umbel. If you wait too long to harvest your seeds, the seed heads shatter and fall. After harvesting, you can separate the seeds from their capsules by rubbing them in your hands.