Getting Started
Here is 60-second video on how to get started.
To grow plants using the Kratky Method, you need five things:
Plants need light to photosynthesize and to grow. Different plants need different amounts of light, but most need between 12 and 16 hours per day. The sun is the cheapest and simplest way to provide light to plants. Indoor electric lighting such as LED panels are also an option but not discussed here. This article is recommended for those who want to pursue this.
The graphic above points out four concepts to understand when choosing the appropriate reservoir.
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Clarifications
- The images are visualizations of volume, and do not suggest preferred containers.
- The volumes in this graphic assume a ‘fill and forget’ approach. If you use a float valve to maintain a constant nutrient water level in the reservoir, the overall volume needed can be much smaller. More information on float valves is provided on the "Bigger Plants" page.
- Some people associate the “Kratky Method” with "quart jars" or "Mason jars" yet this is not something Dr. Kratky has, to my knowledge, ever researched or written about. When I asked him about this practice of growing in such small containers, he said,
It is certainly possible to grow in small containers if they are adequately maintained with nutrient solution. But that takes effort, it is subject to errors and omissions and the roots would rather have a larger area to grow. So, from a practical standpoint, it would be better to grow in a larger tank where all the nutrient solution could be added prior to transplanting.” -Dr. B. A. Kratky via email June 11, 2019 |
Clarifying the 3-6 quart image
a. The small-necked, tall gallon jug is a recognizable volume image and not a recommendation for a reservoir. A low and wide container would be better. b. Dr. Kratky, a scientist, used liters, not quarts in his papers but these measures are similar in size, and are more familiar to an American audience. Metric version available here. c. There is a range here of 3-6 quarts/liters per plant and that is due to environmental considerations. When I first told Dr. K that I used 1 gallon per lettuce, he replied, "I am just curious of your general location. Since 4 liters/plant is always adequate for you, I am guessing it must be a cooler climate.” Very hot climates may need even more than six liters per plant. d. Link to Dr. Kratky's original research: https://www.ctahr.hawaii.edu/…/Three_Non-circulating_Hydrop… |
Clarifying the 5-10 gallon image
I could not find any reference to dwarf or patio tomatoes in Dr. K’s research, but my own experience leads me to believe that dwarf tomato plants can be successfully grown in the 5-10 gallon range. I’m currently growing a Patio tomato in a 10-gallon tub with a float valve. The tomato plant used about 3 gallons (12 liters) to reach the fruiting stage when water consumption will then increase. Dr. K writes: [Full-sized] “Tomatoes typically require 25 to 40 liters of water to produce one kg of fruit. A large tank is needed to support this high water requirement. The expense associated with constructing these tanks limits this 'fill it and forget it' method to an academic curiosity except in special situations.” Link More information on tomatoes on the Bigger Plants page. |
Clarifying the trash can image
Dr. Kratky enjoys experimenting with larger plants-cucumbers in particular. While he has written about using trash cans he usually grows them in low, wooden rectangular boxes lined with plastic. A low rectangle is a better shape for the roots but doesn’t make a recognizable volume image, so I used the trash can icon.
Peppers and tomatoes are tricky since they are perennials in tropical parts of the world but treated as annuals in colder climates. The Kratky method asks that we estimate all the nutrient water a plant needs over its lifespan and size the reservoir accordingly. This is obviously problematic with perennials that can live for years which is why Kratky Method (without float valve) is typically used for annuals (or plants treated as annuals) and not perennials.
Clarifying the one-quart image I left a one-quart container in the graphic as a way to grow seedlings but, as my own experiments have shown (below), small plants such as lettuce will grow much larger in a larger container and require less maintenance. I don't grow any plants in less than a gallon (4 liters). |
But online I saw someone grew a [fill in the blank] in a Mason jar..." |
There will always be people who will grow in small containers and claim it works "just fine". Plants are remarkably resilient and tenatious but having a plant survive and thrive are different things. I encourage everyone to try your own experiment and see what differences you observe in the same plant grown in small and large reservoirs. I urge everyone to size the reservoir to the plant carefully to minimize stress on the plant and maximize plant health.
While tall & narrow containers are easier to find in recycle bins, low & wide containers offer distinct advantages when using the Kratky method as illustrated here.
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The reservoir I use for all my growing is the Rubbermaid Roughneck 10-gallon storage tote. Single totes are hard to find online for a reasonable price, although most hardware stores carry them. You can find sets of eight totes here on Amazon for a reasonable price.
I drill between 1-10 holes in the lids for different sized plants. Most of the time, I drill six holes. I use a 2" hole saw like this one. |
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To prevent algae, the reservoir should be opaque. If starting with a clear glass or clear plastic container, try painting it and see if you can see light through the sides when held up to the sun. While black paint may be best at creating an opaque coating, black also absorbs the most solar energy which can heat up the nutrient water.
Burying the reservoir or wrapping it in a reflective material like aluminum foil or metallic bubble wrap can help keep the nutrient water cool. |
If you're just starting out with Kratky Method, choose small annual plants that are grown for the leaves. Ideal choices include...
Flowers like these zinnias can be grown too! Click here or on the photo to hear Dr. B. A. Kratky explain his method.
Fruiting plants such as cucumbers, tomatoes and peppers are not recommended for beginners but are discussed on the "Bigger Plants" page.
Once you know what you want to grow, you need to have seedlings to put into your Kratky system. The simplest solution, as shown in the video, is to purchase plants from the nursery and wash off the soil. Similarly, one can start seedlings yourself and wash off the soil. Since there are no pumps to clog, a little soil remaining on the roots won't do any damage to the system. Here's a seed starting method that uses the passive "wick" method to keep the soil wet. Seeds need only water (no nutrients) to germinate.
Some people start seeds in rock wool. I personally am not a fan of rock wool for several reasons
You should be able to move the seedlings once they have secondary leaves and are roughly 4 inches/10 cm tall. |
Many people use net cups, coir, expanded clay pebbles (Hydroton) and rock wool in their Kratky system, but I have found reusable "pool noodles" to work best for me. As shown in the video, these are 2-3cm long sections cut from inexpensive pool noodle toys. I purchase my pool noodles from the hardware store or "Dollar store" and each pool noodle makes about 40-50 doughnuts to hold the plant. Typically, I save the cut-out section to act as a spacer for very small transplants. A 2" (5cm) hole saw s the ideal tool to cut holes in your lid to recieve the pool noodle doughnut. Some people run the hole saw in reverse for a smoother cut but I have not found cutting in the usual forward direction to be a problem.
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My most common hole spacing in a 10-gallon Rubbermaid tote. This is perfect for lettuce, basil, bok choi, etc.
While seedlings can sprout with water alone, plants need the proper fertilizer levels in the hydroponic water. Not all fertilizers can be used in hydroponic systems. For example, the "Miracle-Gro" All Purpose Plant Food is fine for soil-grown plants but not for hydroponics. While the major elements of Nitrogen, Potassium and Phosphorus are present, the micronutrients (present in the soil) must be included in fertilizers used in hydroponics. Organic fertilizers are sometimes used in advanced active systems with aeration pumps but are not used in passive systems.
To make matters confusing, some fertilizer companies have created two products with the same name but only one is for hydroponic systems.
To make matters confusing, some fertilizer companies have created two products with the same name but only one is for hydroponic systems.
I have some fertilizer already. It doesn't say for hydroponic use. Is that okay?
Short answer: No, non-hydroponic fertilizer will not work well. Plants need secondary nutrients like Calcium Magnesium and Sulphur. Without these, the plant won't grow well. Also, use tap or well water. Do not use distilled water. The extra trace minerals in tap or well water are beneficial to plants and they can suffer with distilled water.
Short answer: No, non-hydroponic fertilizer will not work well. Plants need secondary nutrients like Calcium Magnesium and Sulphur. Without these, the plant won't grow well. Also, use tap or well water. Do not use distilled water. The extra trace minerals in tap or well water are beneficial to plants and they can suffer with distilled water.
Liquid nutrients such as Fox Farm Grow Big are easiest to dissolve but tend to cost more per dose than dry nutrients. I have never used liquid nutrients but find their ease of use appealing.
Dry nutrients are largely divided by two main manufacturers: Masterblend or General Hydroponics
Dry nutrients are largely divided by two main manufacturers: Masterblend or General Hydroponics
Masterblend is a three-part fertilizer (Masterblend fertilizer, Magnesium sulfate, and Calcium nitrate) Each part can be measured by volume or weight. The ingredients are mixed by dissolving the first two ingredients into water and adding the Calcium nitrate last. Here is an online Masterblend calculator.
General Hydroponics Maxigro fertilizer is a one-part fertilizer and can be measured by volume or weight. It is the fertilizer I use because of its simplicity. One teaspoon or 5 grams per gallon of water for plants listed on this page. I mix the fertilizer into a liter or so of hot water and then use an immersion blender to dissolve it completely. |
If you grow outside, rain can be a problem as it can refill your reservoir, damaging the air roots. Providing a cover, awning, or roof over your plants is the ideal situation if you want to continue growing outside. Here is a photo of the roof I built for my tubs.
Alternatively, one can drill a hole in the side of the reservoir to make sure it never fills with rainwater. Nutrient dilution may happen as the rain water flows through the system though. Use electrical tape or a small cork to cover the hole when needed.
The graphic above and the video at the top of this page should fill in the remaining steps to setting up your garden.
But aren't hydroponics with pumps like Aerogardens or Deep Water Culture (DWC) systems "better" than the passive "Kratky" method?
The comparison can be made to whether a bicycle or a car is "better". Each has its advantages. Where I live, power outages are common and my greenhouse has no electricity, so a passive system is ideal for me.