Kratky hydroponic approach

This is my condensed version of “Kratky Method” a hydroponic approach developed by Dr. Bill Kratky while at the Center for Tropical Agriculture and Human Resources - University of Hawaii, Manoa. The internet is flush with info on this subject. (Their link: There is a wealth of growers information here that goes well beyond just publications by Dr. Krakty. None the less all fascinating reading.

My simple startup shopping list

  • Lights
  • Interval timer
  • grow medium
  • Airpump stone and airline
  • Reservoir
  • Nutrient


The sky is the limit here. Stick with LEDs, Starting out with consumer level lights and Amazon has plenty. With this introduction we are going to stick to Leafy greens which includes Lettuce, Mustard, Arugula and the herbs Basil and Cilantro. This approach also works for Kale but Kale takes a while to grow to a mature size. You can do baby leaf but there are more efficient methods for that. We’ll save that for down the road.

So depending on your space, and what you are trying to light up, choose an option that fits. White light is fine but all you actually need is the red/blue spectrum. While I understand the information on light spectrum and how it influences plant growth, understanding is one thing, communicating that information is another. I am going to try and not recreate the informational wheel. Plenty of material out there and if you decide to continue down the trail it is information we all end up picking up along the way. The key point is plants need lots of light of the right intensity for an adequate daily duration to successfully develop. I run a 16hr light schedule for leafy plants during the winter months. During the summer months I cut the lights back to twelve hours daily but start early shut them off mid-day and then back on late afternoon. Really it is about how much natural light is available where you are growing your plants. Our ambient light in the fall till early spring is horrid, a factor of our latitude and the low sun angle. Most gets filtered by our cloud layer or bounces off the upper atmosphere. Enough space on this subject at this point. You don't need to break the bank but at the same time a good grow light is one of the valuable parts to your entry toolkit.


More photos added soon. Standby

Interval timer

We have a variety and depending on what your are controlling and how much current you require dictates what you buy. For now lets stick to controlling a single light unit. Pretty much come in two varieties, digital and manual. The simplest form has push pull pins and is commonly used to control lights in the house while on vacation. The digital type get more involved and allow for varied programing. As mentioned above under the lights section I run 16hrs of light during the fall winter months. Our long summer days I don't need to light up our grow room all day as there are plenty of windows and I dial back the electric lights to twelve hours split 6 hrs on 4 hrs off during the middle part of the day and then 6 hrs more. All the basic timers can handle this task for a single fixture

Single station programable interval timer. This one is only controlling a single nutrient pump


A manual push pin style timer. Four receptacles are controlling the lighting and the nutrient pump and air pump are running off the always on side. With a single "Kratky" reservoir, you will need two single controls, one for the air and one for the lights. If you have a multilayered system this style works well since you can control up to four individual light fixtures on the timed side and the air on the always on side.

I prefer to use Grodan. Grodan is a sterile rockwool product engineered for water retention characteristics and airspace around the upper root zone. It is made from molten basalt and chalk. Some claim it to be an environmental hazard since it is not biodegradable and it takes large amounts of energy to manufacture. Okay. Let's talk about the destruction of the peat bogs from all the peat extraction. Or coco coir and the vast areas of rain forest that are cleared each year to plant yep you guessed it, coco palm.

Another popular grow medium is a product called Oasis cubes. these are similar in shape to the A-OK Grodan cube which is about one in square and slightly taller than a inch. Oasis cubes are made of an inert foam material. They break apart and make tiny foam spheres. I prefer rock fiber which eventually breaks into smaller and smaller bits. In Hawaii they call this Pele's hair. Too bad we can't extract molten lava and perform the same process.

There are pucks made of Coco Coir. But here is the hitch. Small bits of the coir get loose in the system and clog things up. Not so much a deal with the "Kratky method" since you aren't pumping water. As we get further into other systems it will be evident why this isn't the best option.

Below a sheet of A-OK starter cubes. This is our lettuce cube.


The 1.5" mini block which works well for herbs

For a single tub a small aquarium air pump and a large stone is fine . While not part of the original “Kratky” process injecting air was found to enhance the growth rates. The increased oxygen level within the nutrient getting more oxygen to the roots. The breaking bubbles also result in an increase humidity in the air gap space, which helps to keep the entire root zone moist. Without getting way off track there is also an “Aeroponic” effect where droplets of nutrient splash onto the roots within the air gap from the breaking air bubbles. Suffice to say it does increase growth and most people have accepted it as part of the package. If you decide to run multiple containers you will need a more substantial pump. Here again the world department store Amazon has lots listed. Active Aqua is one market brand. Decent items good durability reasonably priced.

a small air pump for a single reservoir


For a larger reservoir

Reservoir and accessories

Pretty much anything will work for the reservoir. A one quart mason jar works for a single basil plant. But let's start with a four gallon "Sterilite" tub. You want the container to be opaque so as to keep as much light from the roots and nutrient as possible. Algae will grow rapidly in the reservoir when exposed to light. It will compete for food with the roots of your plant.

The pictures here are of a four gallon "Sterilite" tub and lid. This example is set up for herbs or for leafy greens like Arugula and Mustard.

The pictures show five holes drilled with a two and three quarter inch hole saw. With hindsight I would suggest going with four holes. Once you drill the center hole, run your drill in reverse and you end up with a very neat cut. I use the three inch net pot for this application. If you are going to run lettuce I recommend the fifteen gallon reservoir, three holes and five inch net pots.

Lettuce needs space around each plant for lots of airflow. Grey Mold (Boytritis) is a real problem if humidity levels around the plant get too high you end up with wet spots on the leaves and stem where the mold and fungus issues take hole. A fan running across the plants does several things. Suffice to say is is an absolute…well not really but the more airflow the faster your plants take up nutrient and the more nutrient they actually consume the faster they grow. Furthermore with more space also comes more light. This is hindsight. When I started I tried to use the maximum surface space. Even basil benefits from having space between each fully grown plant.

On another note. Just saw something about a fancy new entry into the table top hydroponic units. A full frame lettuce needs a solid 9" diameter space to reach quality size. Two people can consume one of those heads in three sittings. Picking small heads that are cramped together just because you can, does not serve the higher purpose. I may add on this downstream as it is my opinion however let's raise the bar to the highest level. Let's not just produce something at the "Least common denominator" level because it fits the price on someone's spreadsheet. "It's not what we grow but how well we grow it"

Simple startup tub. A four gallon storage tub


Not very elaborate but necessary - The three inch net pot

For this round I am going to focus my attention to Masterblend. It is simple to use, stable and under this application works fine without requiring additional attention. Other nutrient blends on the market require the grower to monitor both EC - electrical conductivity and pH. I want to start with a simple straightforward kit that won’t break the bank and provides a decent amount of success so you can see if you want to dig in a bit more.

Masterblend is actually three parts. The macro and micro part, magnesium sulfate (Epsom salts) and Calcium Nitrate. For leafy greens it is mixed 2 parts A (macro/micro) 1 part B (Epsom salts) 2 parts C (Calcium Nitrate). I prefer to weigh out my nutrients. I use a gram scale and for leafy greens, I find 2 grams per gallon for part A and C and 1 gram of Epsom Salts. provide decent results. Mix each in water separately before adding to the reservoir. Add them in Order A, B, and then C. If you don’t you will end up in a bad spot. Plants won’t be happy either. Let’s just leave it there. Describing "Nutrient Lockout" gets into chemistry levels that are beyond my knowledge base. The key is knowing it happens and as long as you mix the chemistry in the proper order, you don't need to be a chemical engineer.

Good ole Amazon is a source. Epson salt is available locally so you don’t need to include that. Five pounds of the Masterblend and 2 pounds of the Calcium nitrate goes along way if you are mixing say five gallons at a time. Are there organic mixtures. yes, there are and they are seriously expensive to use.

Part A for the Masterblend recipe


Weighing out the nutrient mix

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