How to Grow Hydroponic Onions

The Grand Hydroponic Onions Experiment

**Update** I’m in the middle of another hydroponic onion experiment as of 2/18/2013, and should have an updated post for you soon.  If you don’t want to miss out on that post, subscribe to my newsletter in the sidebar!

I’ve been interested in growing root crops hydroponically, but never taken the plunge.  There are a lot of things that you can grow in a hydroponic system, but there’s not a lot of information out there about how to grow onions, carrots, radishes, or any other root crop.  This is why I’ve started The Grand Onion Experiment!  Read on to check out the setup.


  • Onion sets
  • Air stone
  • Air pump
  • Water
  • Net pots
  • Growing medium
  • Tray

I picked up some red onion sets from my local Home Depot.  The rest of the materials I had from other grows, but you can source most of it from Home Depot and your local hydroponics or gardening store.  You can also improvise and make your own equipment – there are a lot of different ways to do it!

Choosing a System

I decided to go with Deep Water Culture for this experiment setup due to the unique growing requirements of onions.  I also am in love with the DWC method.  It’s a very easy method to learn and also produces some of the most robust harvests that I’ve ever seen.

In my setup I have six 3″ net pots filled to the brim with perlite.  I placed the onions halfway in the perlite and then put all of my net pots into a grow tray.  The only thing left to do was fill it with water and toss in an air stone.

Video Tour

If you’re going to replicate this hydroponic onion experiment, make sure you plant all of the bulbs at around the same height.  This way, you can pour in just the right amount of water so the roots are constantly wet, but the bulbs never touch the water.  I’m not sure how bad that would be, but I don’t want to risk any rotting or decay by having the bulbs sit in water.

Last Thoughts

I didn’t mention in the video that I have no nutrients in my water for the first week.  I read about this trick a few days ago.  The general idea is that by starving your onions at the start, you force the roots to grow a nice, robust system because they’re trying to find nutrients as quickly as possible.  Then, when you finally do add nutrients to the system, your onions have a very healthy, stable root base to help them grow HUGE!

Header image courtesy of SoraZG

Learn how to grow hydroponic onions in this hydroponic root crop experiment. I break it down and you'll be able to follow along as I go!
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18 thoughts on “How to Grow Hydroponic Onions

    • Hey Hugo,
      Thanks for the interest! Unfortunately I had to scrap this project – made a big mistake in letting the bulbs sit in water too long, rotting them out. I also just moved to a new house and had to scrap a few projects due to them being tough to move without ruining them. Don’t worry, more (and better) stuff is coming soon!

  1. Too bad the onions didn’t work out, it’s always hard to keep em out ofthe water and stop them from rotting. Growing onions in hydro is hard as it is but I’ve seen it done before. Try again but be extra careful to keep the bulbs dry, would love to see if this can be pulled off in a DWC.

    • I’ve got a batch of them growing in plain old soil right now and doing a lot better for it. Might bring this experiment back once I’ve got my new system structure constructed – it’s going to be awesome! I think people hesitate to go hydro on root crops simply because they’re so ridiculously cheap you can buy them from the store and not “waste” the space of growing them yourself…but for a fun experiment it’s definitely worth a shot.

  2. Hi Kevin.

    this is a great set up you have here. would this have worked if the bulbs didn’t get wet?
    can you update me on the latest result you got from this setup?
    I’m really interested to grow root crops using the setup you made.

    Thanks, Kevin.

    • Hi Chester,

      Thanks, but I wouldn’t call it a great setup – it failed! I haven’t revisited this experiment yet, but yes, I definitely think that it would have worked if the roots didn’t get wet. That was the real mistake I made – in the ground, onion bulbs generally grow half in, half out of the soil, so they don’t have a lot of moisture on them. I’m interested in giving it another shot actually and will probably test it out in my ebb and flow system.

      Thanks for the comment and please feel free to hit me up if you have any questions or insights 🙂


  3. Hi Kevin,
    I was wondering how long it takes for the onions to grow and be ready for harvest? Is growing onions hydroponically commercially viable, in your opinion?

    • Hey Edmond,

      I haven’t revisited this experiment yet, but I would say that if you want to grow hydroponic onions, do it for fun only. Onions are just so cheap at the store or grown in soil that there’s no real point in growing them hydroponically.

      If you do decide to grow them hydroponically, I’d estimate you cut around 30% of the growing time off just due to the efficiency of growing in a hydroponic system. However, you do have to worry about root rot and all sorts of other issues. It could be a fun experiment though! Thanks for commenting, let me know if you have any other questions!

  4. Hi Kevin can give me an idea of what were the proportions of nutrients that you used for growing onion. Can you send me the charts for its growing period.

    • Hey Sai,

      I didn’t grow these as successfully as I would have liked, so I would go ahead and Google the correct nutrient ratios as anything I would give you wouldn’t be the best numbers 🙁

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