Hydroponic Tomatoes grown using the Kratky Method in a plastic balcony container

About three weeks ago, I started a few tomato seeds, and a single salad seed on a damp paper tissue. A couple of days after sprouting, I re-planted them into a non-circulation hydroponic set-up based on the principles described by Professor Kratky from the University of Hawaii, often referred to as the Kratky Method.


The set-up consists of an 80cm balcony planter without holes (the kind where you’re supposed to drill drainage holes yourself if you want to use them for soil gardening) filled with nutrient solution. As top cover, I used 2 half length (40cm) trays meant to be put under 40cm planters of the same type. The trays are a few milimeters longer than the planter, so for perfect fit, they needed to be shortened by s few milimetres with a saw.


Openings of 5cm in diameter were cut-out in the trays to house 6 net-pods with rock-wool and the plants. At the start, about half of the net-pods should be immersed in water. Later, water level drops as roots get bigger.

While making the holes, the trays cracked in a few places, so the result is not very aesthetic, but the whole thing still holds together. When filled with water, the container becomes a bit wider due to the pressure of water against the sides, which is why I tied a nylon string around the center of the pot. Overall, there are about 2 litres of water-nutrient per plant.

So far, the tomatoes have been doing really well in the this set-up, being at least twice as big as plants from the same batch (sprouted at the same time) that I placed into soil on the balcony (left image below).

Potential problems and obstacles I see in the near future

Two liters of nutrient solution per plant is probably not enough to bring tomatoes to fruit without re-filling, so some topping-up will be necessary. Another challenge I’ll soon have to face will be providing a trellis the tomatoes can climb on. Further, I am not sure if the space left for roots in the hydroponic set-up is big enough for six plant in an 80cm pot.


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5 Responses to Hydroponic Tomatoes grown using the Kratky Method in a plastic balcony container

  1. Winnie says:

    Hi! I’m researching the same methods as you! please update as the tomatos grow! My main concern is how to keep feeding the plant once almost all water is consumed.
    right now I have two peas, one carrot and one spinach growing kratky.

    • urbanfarmer says:

      Great to hear you experiment with the Kratky method too. In the more orthodox version of this method, one doesn’t have to do anything with water, because you use a container big enough for the whole life of the plant. Of course that is difficult if you have limited space. My intention is to re-fill (with water and nutrient) some time before all the water is consumed. I won’t re-fill all the way to the top though, since it is vital to maintain the empty space for the air roots to absorb oxygen. I don’t know how the tomatos will respond to the re-fill, but so far, I tried the re-fill method with thai basilic, and it works just fine.

      Do you have the plants that you mentioned in separate containers or together? I’m asking because from what I read and experienced, having plants with various water needs and strength in the same container can become an issue – the stronger ones suck up the water and nutrients quickly, leaving the slower ones ‘dry’, in which case you have a few healthy plants and several weaklings struggling alongside.

      By the way, I didn’t know a carrot can be grown hydroponically but if it works for you, that would be great news! I had very good experience with beans, so peas should work as well. No experience with spinach, but sounds promising.

      Keep up the good work! I’ll be posting an update soon.

      • Winnie says:

        I’m sad to share that my hydroponic carrot died 😦
        But before it died it was at list 8cm long, so I’ll keep trying in other containers and with different nutrient solutions.
        My peas also died hahaha whole lot of dead plants, but I’ll keep trying.
        My best guess is that the nutrients I was using were not the best choice.
        Here in Chile we don’t have an easy place to buy hydroponic products… Usually you have to research the Internet for Marihuana growing sites, that we have a lot. So I came across one site were they had nutrients specially made for hydroponics
        Now I’m going back to basics with lettuce and other salad greens.
        I normally use bottles and cover them with paper. One lettuce per bottle in different sizes. I do have the space for a big container but I thought I’d try first with small container to get a better view of the process. Hoping one day I’ll be able to grow tomatoes and strawberries.
        How are your tomatoes doing? Can you post pictures or video about the nutrient re-filling?
        Thank you!
        I’ll post something myself and send you the link 🙂

  2. Bill Dempsey says:

    Tomatoes will need about 40 gallons of water during their lifetime. Growing in a two liter container is going to require constant adding of nutrient water. Part of the idea behind the Kratky method is to make growing easy and cheap with minimal ongoing effort. In other words, set it up and forget it. To make tomatoes maintenance free, you basically need to start them in something the size of a garbage can, unless you are ok with adding nutrient solution daily. Also, I’ve heard growing root vegetables like carrots in a Kratky tub is a lot more difficult than growing above ground fruit bearing plants. I’m lazy, so I haven’t even tried to figure it out, yet. LOL

    I’m having good success growing peppers, chives, basil, two types of leaf lettuce, oregano, and cilantro in black plastic file boxes I bought at an office supply store. The boxes are stackable, so the lids are flat. I just cut 5 x 2 7/8″ holes for 3 inch net pots, filled the file box with nutrient solution, and walked away for weeks. These file boxes hold just over 7 gallons of water, so I haven’t had to add solution during the lifetime of any of those plants. The boxes are black, so they don’t let light inside and algae doesn’t grow in the water, consuming all the nutrients. I plan to try peas and cucumbers in my next planting round. I use a small spare bedroom with 4 x multi-tube fluorescent grow light fixtures as my “garden.” This makes it easy to grow without regard to the seasonal changes.

    I grew everything from seeds. I started the seeds directly in the net pots using coconut coir as the medium. The lettuce plants and chives sprouted within 24! hours. Talk about instant gratification. The other plants took 3-4 days to sprout. The growth rate is amazing. I use specialized nutrient mixes I bought at http://www.supplysource.com/Ultraclean-Plant-Food_c_50.html. They’re formulated for Kratky method tub growing systems sold at that same site.

    Best of luck to you on your Kratky setups!

    • urbanfarmer says:

      Thanks for very good points, Bill. Yes, I think it would be a lot easier and less care-intensive to grow in larger boxes/containers.

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