What About Kratky?

Among hydroponic growers, Kratky method is too often seen as a lesser method, inferior to others. Nothing could be farther from the truth. It is just as effective as other methods and, unlike many, is quite close to how plants grow in nature. It is sometimes more effective than more technically complex methods that grower don’t understand completely. It is certainly the biggest bang for the buck.

Everyone’s heard of it, but many know only bits and pieces or believe it’s just Deep Water Culture without pumps.  I want to cover the nature of Kratky method, how it works and its few but essential requirements, as well as how to decide if it offers benefits for your situation.

It is a new method. Really it is a new perspective, rather than something entirely new. But as a recognized hydroponic method, it was only introduced in 2009 when Bernard Kratky of the University of Hawaii published the first academic papers and began speaking internationally. He called is “a suspended pot, non-circulating hydroponic method.”

B.A. Kratky, Researcher Emeritus

 

Dr. Kratky’s interest was the development of an effective hydroponic method that required little technical skill, could be constructed using a variety of commonly accessible materials and could be operated to full growing advantage off-grid, using no pumps and consuming no electricity when done outdoors or in a greenhouse. A perfectly good Kratky system can be built with odd pieces of lumber, some sheet plastic and a piece of insulation board or similar. Basically construction leftovers. But it would be a mistake to assume that compromises had to be made to take the method to the third world. It is as powerful a tool as any system using pumps and purpose-made equipment.

Some hydroponic methods make significant compromises. Nutrient Film Technique accepts many technical difficulties and critical design and operating issues, some of which have no best choices, and all options having shortcomings. But all that – and it grows no better than any other system – is accepted in order to save vertical space that adds up to real revenues in very large commercial operations.

Kratky makes no compromises. It fully satisfies every plant requirement. That should not surprise when one really compares it to other methods. In Krarky method, roots get their air as atmospheric air. That is exactly how roots get air in NFT, Dutch bucket, drip medium methods and ebb and flow. It is also how plants in natural soil get atmospheric air that circulates among soil particles. The only different is that in Kratky, there is simply no medium surrounding the roots getting air. They are suspended in free air. (They do not dry out, because the lower roots are watered, and the air above the nutrient stays moist.)

But roots must be fed, must have access to soluble nutrients. Dr. Kratky’s insight was not that roots could use free air but that there was a simple way to provide nutrient that didn’t involve having to pump nutrient solution in and out as in ebb and flow. That is the essence of Kratky method. A substantial root mass is suspended in free air, while the lower root mass is submerged in nutrient solution. It must be done right, and we will see how that happens.

We will examine what an established Kratky system looks like, as well as how we get a new seedling settled into such a setup.

A Kratky setup is very simple. Many resemble DWC buckets with the plant in a net cup and roots descending from the net cup into the bucket. The difference is that in Krarky, the roots descend first into free atmospheric air and on down so that the lower roots are in exactly the sort of hydroponic nutrient used in DWC. There is no air pump or other mechanical aeration, because roots don’t need air from the nutrient solution. They have the air above it.

I should point out that all plants must be allowed to adapt to one or the other mode of acquiring air, dissolved air or free air. There are differences in root structure and function for each mode. They cannot do both at once, and they can’t shift from one mode to the other without tedious procedures that hope to keep them alive long enough to change. Of course, like many things, very young plants adapt very easily, and as we will see, getting a seedling started in a Kratky setup requires nothing very special.

Before getting into particulars about construction and operation, I should first give you a chance to see if you want to use Kratky method. What are its advantages?

Cost. Kratky is the cheapest imaginable hydroponic methods, except, perhaps for pots sitting in trays of nutrient. The world is full of potential materials. Various sizes of plastic totes are very popular, and reservoirs off all sizes are offered daily on online sites like Craigslist as food service surplus. Nothing to spend on pumps, and even float valves can be made using old food containers and scrap pieces.

Off-grid operation. Not just for back to nature types and third world villagers. A Kratky system can be operated without electricity anywhere where the environment allows growing. So, it can be placed anywhere in a yard or property and can be moved around at need. For example, I want to grow melons, but I don’t want to just let them run into grass, so I can put the vessel on my concrete patio. I can also move a Kratky bucket or barrel into the greenhouse in winter and move it back out to the yard in spring. With Kratky, you can position your favorite plants along the walk or close to the kitchen.

You can grow pretty much any plant with roots. Containers for Kratky method can be selected for lettuce and greens, vining food plants, tomatoes and peppers, and even trees, if one really wants to. Kratky works with buckets, barrels, channels like fence post, totes and shallow broad and long trays for greens and herbs.

Potentially very low maintenance. This is a difficult topic, because of different plant sizes, different reservoir sizes and different environments. But it is true that, in most places, with a sufficiently large container, it can go a season without service. However, when a smaller container’s level is maintained by a float valve from a larger reservoir, one can go a very long time without attention to the nutrient. But note that Kratky may require actually more service in small containers, because you only get to use about one-third of the container for nutrient. More on this later.

The possibility of growing without constant attention is often associated with Kratky method, but it is just as much a possibility with other methods. What we must consider is how much water a plant needs over the course of its usual useful life. We are seldom aware of this with most other systems, because we are accustomed to replenishing nutrient manually every so often.

Full size tomatoes require 25 to 50 gallons of water to produce one kilogram of fruit. But some tomato plants can run out of water in a 50-gallon barrel. Vining plants like cucumber and squash will also use as much as 50 gallons. Those are large containers, but people do grow in them using Kratky method and achieve great yield with little service.

Why do we see this in those Krartky systems but worry about deterioration of nutrient profiles in other systems? It is because we so often do that growing in smaller reservoirs. Small growing tanks will change rapidly, because each unit of water or nutrient taken by the plant is a relatively large percentage of the while tank’s volume. There is no magic in Kratky that changes that.

There is however a lesson that plants do adapt to changing nutrient profiles when it happens over a long period. The nutrient in a 60-gallon barrel with a large pepper plant is far from what it began with at the end of the season. Yet such plants do thrive for the whole season and are healthy and productive months later. But remember that if they were in a 5-gallon bucket, the nutrient would likely have been serviced and replace every two weeks. But the five gallons is only one-twelfth of 60 gallons. Two weeks times twelve is 24 weeks, five months, a full season. The sixty gallons will be affected at one-twelfth the rate of the nutrient in the five gallons. If five gallons of nutrient can go two weeks, 60 gallons can go 24 weeks. So, five months between maintenance is not unreasonable to expect in a mild climate.

That may or may not be quite right in reality. It may well not work out that way in the dessert heat when water losses will require adding plain water from time to time.

Because Kratky growers have a greater expectation of less frequent maintenance, they lave learned an important lesson. That is that low, wide tanks are better than tall, narrow tanks. In other words, totes are better than buckets. The reason is that, for the same volume of water/nutrient lost, the low and wide tank’s level will drop less over the same period. This can easily double the interval between required service, even when it’s low wide versus tall narrow smaller volumes. It also allows a new plant’s roots to reach the nutrient much sooner.

But using a reservoir and float valve to replenish grow tanks offers both greatly extended service periods and the ability to use smaller volume tanks effectively. What kind of solution is being used to replenish can be tailored to the local conditions. In an environment where water losses are high, plain water or weak nutrient can be used to replenish growing tanks that began with standard nutrient. Where water loss is relatively low, something closer to standard nutrient can be used to maintain volume.

This also makes it possible to use the favored way to grow greens and such, which is in broad, shallow, long trays. Normally, such shallow trays would require almost daily service. But with a reservoir and float valve automatically maintaining the level, they are perfect, because such shallow trays mean roots quickly reach the nutrient and spread out in it. By shallow, I mean on the order of six inches or so. And with such trays, tray volume for area is low enough that a modest reservoir can keep it maintained for a long time.

The reservoir and float valve system even allows the Kratky grower to start seedlings and transition to permanent conditions without intervention. Of course, to start new plants, trays are filled up to the net cups, and nutrient is allowed to drop naturally as root descend. But the float valve can be on duty from the start and will not activate until the level drops to the desired two inches of a six-inch deep tray. From that point, it will hold the level constant. Nothing for the operator to do.

A further refinement can extend the time the system can be unattended. A second float valve in the supply reservoir can keep it up to a chosen level by automatically adding water from any water supply. It will, of course, progressively dilute the reservoir, but it can be set at a low level to ensure that the system cannot go completely dry. Plants can stand a period of low concentration before the operator returns to intervene.

I should point out that float valves should always be in a control or guide bucket separate from the growing tank, so that they cannot be fouled by roots and kept open. And it should be taken as a given that, no matter how large the growing container, some plants will likely require replenishment by float valve, and to insure proper nutrition, a change of nutrient may be appropriate at the time blooming and fruiting begin. And of course, the addition of any amendments, like additional cal-mag, found to be needed by the cultivar of choice.

The commonly accepted practice, proven by long experience to work well, is to reserve the top two-thirds of the growing vessel for roots in air and to use no more than the bottom third for nutrient solution.

New Kratky growers often worry about how a seedling is supposed to start in a Krartky tank when the tank must be filled to the top to reach the new plant’s very short roots which may not have fully emerged from a net cup. But the new plant’s needs are small, and nutrient can reach the bottom of the net cup medium and leave only the rest of the net cup for the young roots to get the little air they need. Nutrient will begin dropping naturally from consumption and evaporation as the roots begin descending to follow it down. As it goes, the falling nutrient level leaves behind a growing mass of roots in free air. I have never had roots fail to keep up with the falling nutrient level.

Dr. Kratky’s original demonstration placed the new plant in a floating foam raft. The raft dropped with the nutrient level, but at the desired point, it came to rest on supports that kept it from dropping farther. The nutrient kept falling, though, leaving the necessary air space. This answered any concern about roots growing sufficiently in the beginning.

I should also mention the “Mason jar Kratky” demonstrations of which there are many online. While they are cute and do work, you should expect to have to maintain the nutrient level very frequently. Remember, because of the one-third rule, you will never have more than about ten ounces of nutrient. One gallon is the more appropriate size container. And if you’re area is hot and dry, you may want more. The larger size plastic coffee cans are good for one lettuce plant. It’s just a matter of if you don’t mind attending to them more often and accept not being able to leave on vacation without someone caring for them. But you should also be aware that, when containers are very small, size does matter, and experiments have shown that lettuce in a 7-quart container with no servicing will grow twice as large as a one-quart container refilled every four days for three weeks.

Now, Kratky is not a universally great method for everything, but then no method is. I use four ebb and flow trays full of LECA for strawberries, because that is a nearly perfect setup for moving new runner plants, adding new bare root plants and for the close spacing I want. Kratky would be possible, and I would do that if I needed it to be off-grid. I’m just using the method that seems to offer the best features for the job.

And that’s really what this is about. It is to let people understand how Kratky really works and how to make it work well. But it’s more about the common requirements that must be met for all growing. The issue of larger reservoirs and float valve continuous replenishment apply to most methods, although not all methods need them and not all growers want them.