Hydroponic Lettuce–Kratky Method

This method uses no air pumps or water circulation pumps.  In a nutshell:  A shallow tub is filled with water and nutrients.  A piece of styrofoam with 9 2” holes is cut to allow it to sit on top of the tub.  It does not float on the water in the tub, but sits on top of the tub perimeter.  When the lettuce has sufficient root stock the grow plugs are placed in 2” net pots and these are deposited in the 2” holes in the styrofoam.  These base of the net pots will sit in the water.  As the plants grow the water level will go down but the roots will also “grow into” the water/nutrient solution.  The plants are supposed to generate small roots that will acquire oxygen from the air space that forms as the nutrient level drops.  Stay tuned.

5/26/13 started lettuce from seed.  two seeds per plug.  will thin out the weaker plant later.  
5/30/13 Ordered some store display shelving constructed from heavy grade plastic.  It easily snaps together, is 36” tall and its shelving comes in solid or grid form.  I chose the grid form.  It is the perfect height for a potting table and to hold trays of seedlings.  You can buy it online at:  BENCHMASTER
These racks are like lego toys.  A great concept.  Be sure to look around.  They have many configurations. 
6/04/13 lettuce in grow plugs.  The plug without lettuce never had any seeds.  It was used to block sunlight from entering and causing algae.  These are grown outside and receive about 4 hours of direct sunlight a day.  Roots are forming and these should have enough root mass in another week to be put in the final grow tray. IMG_0394
6/7/13 What you will need: 
1.  a suitable tub
2.  styrofoam
3.  2” net pots (shown in assembled picture)
4.  2” hole saw
5.  9 lettuce plants grown from seed in “grow plugs” – must have sufficient root mass for the roots to reach the water in reservoir. 
6. nutrients – mix according to their directions.


  Based upon the size of this tub I decided that it could handle a total of 9 Lettuce.  Sizing is based upon space needed to accommodate lettuce as it grows rather then reservoir size. 

Laying the tub on a sheet of styrofoam I traced the outline of the tub and cut it 2” larger on all sides.  This styrofoam will not float in the reservoir but will suspended above it.  I then place the 2” net pots on the styrofoam to determine the drill points and drilled the 2” holes.  In styrofoam there is no need to drill in reverse as when drilling into plastic/pvc.  The 2” netpots have a lip that will extend beyond the diameter of the hole.  This will then keep the netpot from falling through the hole.  As the lettuce grow it might be necessary to place additional support under the styrofoam panel to keep it from cracking.  

2” hole in styrofoam – no net pot

two netpots placed in two of the 9 holes

side view of styrofoam panel with net pots suspended in place.

styrofoam panel with net pots above reservoir.  Be sure when drilling 2” holes that they are within the perimeter of the reservoir.

panel resting on reservoir. 

  Use a old plastic one gallon jug and fill the reservoir to the top leaving about a 1/4” gap.  Based upon the nutrients I am using I will mix 2 tblspns per gallon. 

Place the grow plugs with plants in each net pot.  It should not be necessary to add more water or nutrients, but as I write this I am thinking that 9 plants in this size reservoir might be too many for the reservoir to supply adequate water.  If that should happen then I will have to add nutrients/water from a standby reservoir.

As you might have noticed this setup requires no electricity – no air pump no recirculation water pump.  Again I read about this method and was impressed enough with the results that I thought it might be worth the effort.  Its cheap too.

If you have an open hole you need to plug it.  I should have kept the styrofoam plugs that were generated when drilling the holes.  If you don’t plug it then you will have an algae problem.  The algae will coat the roots and have an overall undesirable effect.

6/8/13 Lost all tomato and lettuce seedlings due to high winds.

Was forced to start lettuce seedlings over and will wait until cooler weather to “restart” tomatoes. 

6/21/13 New seedlings doing well. IMG_0452
6/28/13 Some seedlings did not germinate so I am transferring the plants that did to the new “tub” IMG_0453
  They look like they took a hit but I feel they will recover just find.  What happened is that the water/nutrient level dropped.  I added more to raise the level and all is fine.  IMG_0454
7/12/13 9 plants for a container this size is too many.  will drill a new styrofoam board for 6 plants.  I harvested these keeping 2 for myself and giving the rest to my neighbors.  I am done until October.  The weather is just too hot even for lettuce.  I would give this method an A+ for growing lettuce – no water circulation pumps and no aeration pumps.  Just keep an eye on the water level, especially in hot weather.  The plants take up a lot and you will have loss due to evaporation.  IMG_0485
4/5/14 Started another Kratky setup for lettuce.  This time I am growing 3 heads of Romaine.  Each has been grown from seed and started a few days apart.  I am hoping that this staggered approach will provide a long term supply rather than 3 heads at once.  I am using yellow foam plugs in the 2” empty net pots to block sunlight from entering the pan.  The net pots with the plugs can also be easily lifted to add more water/nutrient as needed due to plant uptake and evaporation.  Also started two tomato plants from seed.  These will be transferred to a dutch bucket setup when they achieve a little more growth.  IMG_0655IMG_0654
4/10/14 Look at the root mass on the front right lettuce compared to the smaller left rear lettuce.  Same lettuce variety but different root mass hence bigger plant.  Just be sure to keep the water/nutrient level up to max fill.  In this container that is about 2 inches below the styrofoam.  IMG_0010IMG_0011
Above is the front right plant.
Above is the right rear plant.  Much smaller plant and root mass. 
4/13/14 modified the kratky method to utilize an air pump with two air stones.  The lettuce develop at different rates using the kraty method.  I wanted to see if all of the splashing caused by the air stones would encourage faster growth.  I also dropped in a grow plug with just a single seed.  The splashing should keep the plug wet and encourage growth of the lettuce from see.  I am curious to see if there is a “speed up” from seed to fully developed.  IMG_0023
the brown plug in the picture is a grow plug with a single lettuce seed suspended by a 2” net basket.  The air stones should “splash” this plug and growth should progress.  Before I had to grow them in a seedling tray and then transfer to this setup when there was sufficient root mass.  I am now hoping to avoid this first step.

A longer shot of the reservoir with an air pump to the side (covered by a shoebox side piece of plastic – weather proofing).  The actual air pump has two outlets feeding to airstones in the reservoir.  The airlines enter the side of the reservoir above the water level Open-mouthed smile

4/22/14 Romaine lettuce using the modified kratky method (used two airstones with aquarium pump).  Outstanding performance.  IMG_0052IMG_0053
4/30/14 One Romaine lettuce from the Jurassic Park Period!!  Remember this one started out as seed back on 4/5/14.  Now just 25 days later.  IMG_0059
5/5/14 harvested the lettuce.  1 head of romain.  Don’t suggest letting it go the extra 5 days.  4/30/14 would have been the cut off day. IMG_0010
4/19/15 I am using inserted bubblers to aerate the nutrient solution.  Growing lettuce and bok choi (not shown).  Good healthy roots.  Reservoir in this pic is low so time for a refill.  I keep 30 gallon Brute cans filled with water with a PH of 6.2 and a PPM ~1100.  IMG_0236IMG_0240IMG_0237


Hydroponic Lettuce–Kratky Method — 9 Comments

  1. Thanks for the “atta boy”.

    I pretty much shutdown everything after the end of July. The water temps became too high and the plants were adversely effected. I will start up again in October. The thing about lettuce is to come up with a staggered planting/seedling cycle so that all the lettuce does not develop at the same time. If you don’t plan this then you will have a “whole bunch” of lettuce ready at the same time.

  2. I have a foam Hydroponic system and is has a circulation , so it sorta a floating foam hydroponic system. Well i like your system but if you tried it using the lower part in foam or wood with black plastic liner inside i think it would not have been as badly affected because of the hot weather. The plastic tub hydroponic system is going to heat up much more then wood and maybe foam and sooner too, i wonder, what do you think? If you try doing a solar and also kratky method hydroponic in large scale? Have you seen any plans or ideas for a greenhouse design based on Kratky method? I would like to build one which uses low power but produces a lot. Thank you, iain in Thailand at thairockshop

  3. iain,
    Thanks for taking the time to comment. I have seen wooden “box” structures which are lined with 3 mill thick plastic sheeting to hold water. I agree that this type of construction would be less effected by heat. Where I live would be ideal for solar but the initial setup can be quite expensive. Living near the ocean like I do would be well suited to a wind turbine, but then I have to meet certain building requirements. I have not seen a green house that supports the kratky method. But I am certain you could build one yourself. I guess you want to keep the plants protected from insects and a green house would offer that type of protection.

    The kratky method can be used for growing other types of plants. Not just lettuce. It is inexpensive in that it does not require electricity – no water circulation and no air to splash the root base. Give it a try. I think you will be pleased with the results.

    Yous said you use a floating tray in your setup up. That method is effective also, but because there is no air space you have to have bubblers to oxygenate the roots and that means you need electric nearby. With kratky you do not need to worry. Just make sure that the you plants have roots long enough to reach the water and be sure to keep the water level steady. The plants will take up a lot of water and in hot weather you will loose water to evaporation.

  4. Thanks Ron,
    Yes i have had the same setup for the past 4-5 years, I got it in Thailand from a local big hydro farm. It is about 14 ft long 4 ft wide, has metal frame to hold the foam troughs, 4 in total, which are then lined with thick plastic, 6 mil? Then it has a slight angle to the entire table. one end i have a garbage can dug into the ground about 2 ft, sitting shaded under the foam table. Works in warm climate, the above unit then has a drain at the low end feed a tube which return the water to the can below. A fountain pump and pipe bring water to the foam table at the higher end other end of the drain. No aerators used but one pump which yes must run 24hrs a day. I have lost power half day without losses but they all did wilt. I have tried all kinds of plants. The top has a plastic mesh nylon screen to avoid insect and a platic clear liner to avoid rain. It work great but i am ready for the Kratky method and would like to do it on a big scale, for family food and possible market sales

  5. iain,

    Wow!!! You have quite a large setup. I am just starting out.

    here is a link (http://www.youtube.com/watch?v=oDYeffYcVkY) to a short video on the kratky method. This is where I got started with the kratky method. It pretty interesting. Also if you want to “grow” something else to enjoy with your hydroponic vegetables you can try this link: http://www.lonesomecow.org. Its another site of mine on how to make “mead” (honey wine) from honey if your interested. :>)

  6. Hi Ron,
    Yes very interested in the honey, Do you have bees? I want to get them ASA i get home to USA, I am looking specifically for any melipona bee species. The are amazing tiny little things, like flies, I can stand in the middle as the swarm and the just run into me and fly off after getting stuck, I am putting a video soon but over 100 species exhist many from mexicp and texas so i want to find a texas one and keep them in my warmed green hpuse year roound. The produce a hony 4 x less and 5 times more expensive, they also are great for local polination like in greehouse andhtey dont die, the Japanese have been buying them and importing them from thailand. I think we should find some local us species.

  7. I’m in Ky and in the process of building a hoop house in which I plan to grow greens this winter. What I have never been able to find is what are the min and max water temps to grow the greens? What is ideal?

  8. John I am in Fla. Most of my hydroponics comes to a stop around July. The water temps in their reservoirs get to about 90+ degrees and while the plants don’t die they don’t grow or produce fruit. They just “sit” there. I just started some lettuce and tomatoes from seed yesterday since we are moving into fall. I use a product called “Reflectix” to wrap the reservoirs to keep the direct sun of them and to keep them cooler. I don’t recall seeing anything on an ideal water temp. I don’t believe a hoop house will provide very much insulation against the winter cold so you might have a problem. One guy used aquarium heaters in his reservoirs. I would think water temps around 50 would be ok. This will be my first fall/winter effort. I usually start in March and go though July.

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