How to Grow an Onion from an Existing Onion Indoors

Two Parts:Germinating the OnionTransplanting the Onion

Growing onions is fun and interesting, but purchasing onion seeds or bulbs can be an extra hassle. Instead, why not grow an onion from an existing onion?

Part 1
Germinating the Onion

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    Cut off the bottom 2 inches (5.1 cm) of a large healthy onion.
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    Soak in compost tea or other liquid fertilizer for an hour.
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    Let it sit in paper towel that has been dampened with 0.5% dilution of hydrogen peroxide. The hydrogen peroxide fends off mold and rot while creating dissolved oxygen which speeds up germination.
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    Spray the roots with a 3% dilution of hydrogen peroxide every other day. Let sit for 2 minute before washing it off
    • Once the heart of the onion has grown 1 to 1.5 centimetres (0.4 to 0.6 in) tall, it is ready to be transplanted into a pot.

Part 2
Transplanting the Onion

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    Trim the excess onion with scissors. Leave a 1 to 1.5 inches (2.5 to 3.8 cm) border around the central growth.
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    Bury the onion so that the top is 1 to 1.5 centimetres (0.4 to 0.6 in) below the surface
    • The soil should be two parts potting mix to one part compost, with a layer of pebbles at the bottom of the pot for drainage
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    Spray again with the 0.5% hydrogen peroxide dilution.
    • Within three days, expect to see a shoot beginning to emerge.
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    At this point, you may now treat this as a regular onion.


  • Feed once a month with liquid fertilizer in order to speed up growth.
  • As the onion grows, transfer it into progressively larger pots.
  • It's best to use onions from a local or organic market as these will generally have better results.


  • Avoid overwatering, as it can lead to root rot. This can be prevented with weekly waterings of 0.5% or less dilution of hydrogen peroxide.

Things You'll Need

  • Onion
  • Compost tea or some other liquid fertilizer
  • Paper towels
  • Hydrogen peroxide, both in 0.5% and 3% dilutions
  • Suitable pot(s)
  • Scissors
  • Potting mix
  • Compost
  • Pebbles

Article Info

Categories: Growing Vegetables