Glass Jar Kratky Hydroponics UPDATED

Introduction: Glass Jar Kratky Hydroponics UPDATED

I've been wanting to have a go at hydroponics for AGES but lack the space or a greenhouse to build a proper pumped setup. I have an East facing bedroom window and a large South facing office window which get a lot of sun.

I read about the Kratky method on the Hydro Reddit. It requires no pump for nutrient flow or air stone for oxygen supply to the roots. The basic theory with the Kratky method is that you provide the nutrients and as they're consumed the water level in the plant's container drops. In this air space the plant develops oxygen absorbing roots and below the water line it develops nutrient absorbing roots. Kratky's original paper can be found here.

A lot of the Kratky hydroponics setups I've seen on the internet use large plastic containers and set the plants in their net cups into the top of the lids. Being on a window sill I didn't want anything too large and so the obvious choice was glass jars. They're small, free and easy to obtain. I wasn't sure there'd be enough room for root growth but with little to lose but a few pennies worth of seeds and nutrient soloution, I thought why not try.

As a plus, the fact that the jars are clear makes this take on the Kratky method a great way to teach others (and myself) about it. Kids and adults both seem to get super excited when I take off the cardboard light covers and they see the roots.

This Instructable is meant as a place to leave photos I've taken of my experience so far. There's LOADS of material out there to read if you want to give it a go yourself. I'll update the pictures and descriptions in the future as I learn/try more.

Updated 22/06/2014: with photos of much bigger pepper plants, new pak choi and a second crop of french beans.

Step 1: Materials and Outlay

Here is a list of the materials I scavenged and the materials that I bought:


  • 1L of 2 part nutrient solution. I chose Aqua Vega, a formula specifically for leaf/plant growth as opposed to fruit growth. This is enough to make 200 L of nutrients. (£13)
  • 25 off 5 cm mesh pots
  • 10 off 8.5 cm mesh pots (£2.70)
  • 2 L hydroton growing medium. These are expanded clay pebbles. (£2.50)
  • Black spray paint. To make the top of the jars opaque and inhibit algae growth around the roots. (£3)


  • Small glass jars. Mostly 400 g pasta sauce jars from my culinary challenged student friends.
  • Large glass jars. A local fish and chip shop saved the large 1.5L jars that their pickles come in.
  • Thick card to surround the jars and keep the light out.
  • Various seeds I had laying around from planting my vegetable patch.
    • Chilies
    • Peppers
    • French beans
    • Basil
    • Pak Choi

Total: £21.20

Step 2: Method

From reading online, most people will start their seeds in little rockwool cubes soaked in water. I didn't have any of those and could only buy them in bulk online. I started my seeds on a couple of sheets of tissue paper, folded over.

Growing On:
Once there were some roots visible I teased them out of the tissue paper and put the seedlings in net cups with hydroton. Carefully. I did try supporting them with cotton wool but that seemed to slow root growth on the first batch of chard that I grew. It also turned really mouldy... probably not good!

Step 3: French Bean

This one was just for the hell of it. French beans didn't do very well outside in my garden last year and I had 3 seeds at the bottom of a bag. So I germinated a few just to get rid of them and because the nice large seeds would be easy to transfer. Only one germinated and he seems to be doing very well so far.

You can see flowers and beans on the fourth picture. 12 were pollinated, 8 grew to full size, the others fell off.

Updated 22/06/2014: New picture one, the French bean plant produced a second crop of beans. 10 in total all growing at the same rate whereas before I had 2 or 3 big ones and a smaller 6. Still not used a fruiting formulation of nutrients and it seems to be doing well. The sun makes the leaves look very yellow in that photo but they're actually a deep green.

Step 4: Basil

The basil's by far my favourite. The leaves are huge and a really deep green. Whenever I've grown basil in pots I've had small yellowish leaves. It's doing so well I've decided to grow a lot more of it in individual jars. More pictures to follow once they're all thriving too!

Update 22/06/2014: Pictures three and four show the basil growth.

Step 5: Chillis and Peppers

I started three varieties of peppers/chillis:

  • California Wonder
  • Marconi
  • Purple Tiger (a purple chilli)

I decided these would need more room so they're in large 2 L glass jars that used to house pickled onions, eggs and gherkins. Wanting them to look smarter on my work window sill I decided against just wrapping them in black polythene. The top curved part of the jar has been sprayed black to keep light out. The bottom half is covered by thick black card so that I can easily have a look at the root health without pulling the mesh pot out.

I've got 8+ of these on various window sills. I'll update with pictures as they grow. I'm a little worried that the pH/nutrient concentration will vary too much as the water is consumed and they won't do so well. I couldn't find peppers done with the kratky method online so it's a bit more of an experiment.

Step 6: Chard

Some pictures of some very healthy looking chard roots. You can see the white fluffy oxygen absorbing roots at the top. These plants weren't in a dark enough container. I had them in a small white trough which had a gap around the top. I think the light caused too much algae growth, the roots then turned dark and the leaves wilted. No more chard :(

Step 7: Pak Choi

Four week old pak choi.

Step 8: Lessons

I've learned quite a lot in the couple of months I've been playing. The most important lessons being:

  • Cover the roots. If light gets into the jar, algae growth can inhibit root growth and nutrient uptake. I had some chard die on my when I used tin foil (which ripped) instead of thick card.
  • Cotton wool and tissue paper wraps to grow the seedlings on from when they sprout is a bad idea. They seem to go mouldy very quickly. I have had much better results just letting the seedlings get much bigger and then transferring them straight to the growing media (hydroton or perlite)


  • I'm not sure how well my peppers will do. The Kratky method is recommended for non-fruiting vegetables since you don't, or aren't meant to, change the nutrients. I've read that a different nutrient solution should be used while fruiting for optimum growth. Time will tell!

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    3 Discussions


    2 years ago

    • Cotton wool and tissue paper wraps to grow the seedlings on from
      when they sprout is a bad idea. They seem to go mouldy very quickly. I
      have had much better results just letting the seedlings get much bigger
      and then transferring them straight to the growing media (hydroton or


    4 years ago

    Nicely done, I like your approach. Not having to drill plastic is great. My wide mouth mason jars (3 inch openings) work great for this.