DIY Hydroponics Systems — Kratky Method, NFT, and DWC


Hydroponic systems encompass a variety of techniques for growing crops sans soil! Hydroponics incorporates the use of a water-based nutrient supply and optionally (albeit encouraged), a growing medium for the roots to latch onto. The five essential elements of a beginner’s hydroponic system are as follows: some fresh water, oxygen, a growing medium, nutrients (don’t fret—we’re not abandoning those NPK ratios), and of course, light. Potential growing mediums include minerals such as perlite or vermiculite, coconut coir, peat moss, or rockwool.

Benefits of using a hydroponic system include the ability to grow anywhere and anytime, a more efficient use of water, fewer required resources, and higher yields in less time.

There are several popular methods for producing viable plants hydroponically. These include the Kratky Method (we will discuss a couple different versions of this method), the Nutrient Film Technique (NFT), and Deep Water Culture (DWC). Each of these employs water as the primary vessel for nutrient acquisition, with subtle discrepancies in delivery methods.

Kratky Method: Mason Jar

The Kratky method is a simple approach to hydroponics, suitable for beginners or those of us who are likely to forget about (or plain neglect) our plants. Plants that grow successfully using this small-scale Kratky system primarily include herbs, such as basil, oregano, cilantro, mint, parsely, and chives.

When employing Kratky’s mason jar method, you will need 

  • Large mason jar. An opaque mason jar is best, as it prevents sunlight from reaching the roots. You can paint your jar or wrap it with tape or paper.
  • Net pot (net pot sizes range from 2–10 inches). This is going to hold your growing medium and your plant. 
  • Growing medium. As mentioned above, this may consist of perlite, vermiculite, coconut coir, peat moss, or rockwool.
  • Lid for your mason jar. This can be plastic or styrofoam if you do not have access to a drill. 
  • Hydroponic fertilizer. 

The set-up is as follows:

  1. Calculate the amount of water and nutrients needed for your plant based on the needs of the plant you are growing and the volume of water you intend to use.
  2. Make a hole in the mason jar lid that is large enough to hold the net pot, but small enough that it will not fall all the way through. The lid prevents evaporation of the plant’s water reservoir. 
  3. Fill the mason jar with fresh, clean water, allowing an adequate air gap between the top of the jar and the water line for your plant’s roots. 
  4. Add your fertilizer, and stir! The pH of your water should be between 5.5–6.5.
  5. Place your net pot with the growing medium and plant in the hole in your lid. The roots should be partially submerged and partially exposed to air. It is important that not all of the plant’s roots are submerged to facilitate respiration.
  6. The air gap will grow as your plant grows; its roots will extend farther down as it uptakes more and more water and nutrients. If you are growing a Kratky-method-approved plant (a small, quick grower), it will likely be ready to harvest by the time the water is nearly depleted.

Kratky Method: Five-Gallon Buckets

The methods outlined above are ideal for the smallest, fastest-growing plants. If your goal is to grow something just a bit heftier, such as leafy greens like lettuce, kale, or spinach, you should opt for a five-gallon bucket instead of a mason jar. 

The set-up is largely the same, but everything is just a little bigger. For example, a five-gallon bucket is going to replace your mason jar. Additionally, your net pot for a leafy green should be larger than your net pot for an herb. Your water and nutrient calculations will also be different for your leafy greens and a larger system. 

The preparation method is exactly the same as above, but nix the mason jar, and use your five-gallon bucket in its place. You may require a drill to create a hole of adequate size in a five-gallon bucket lid. Alternatively, you can use plastic or styrofoam.

Nutrient Film Technique

The Nutrient Film Technique, sometimes described as a “nutrient slide,” utilizes running, nutrient-rich water delivered by a pump in a closed system. Similarly to those used in the Kratky method, NFT works best with fast-growing plants that require little support, as the roots are not suspended in a medium and therefore, provide little support.

Growing greens with Nutrient Film Technique.

The essentials for setting up an NFT system include

  • Reservoir, such as a bin. This holds water and nutrients.
  • Submersible water pump. This pushes water and nutrients up to your plants.
  • Two pieces of tubing. One of these connects the nutrient pump to the grow trays, and one returns the used nutrient mixture back to the reservoir. 
  • Grow tray or channel. This is what holds the plants and allows water to run through.
  • Net pots and a growing medium. The net pots hold the growing medium, and the grow tray holds the net pots.

The NFT system has a slightly more complicated preparation process than the Kratky system, but utilizes the same basic principle of keeping plant roots partially submerged in water to offer them access to nutrients and oxygen. Below is a simple outline of how to set up a system that employs the Nutrient Film Technique.

  1. Build or purchase your grow trays. While many growers successfully use PVC pipe, a flat-bottom channel, such as a gutter, provides a larger surface area of water over which roots can spread. Avoid any tray with ribbing on the inside, as this can lead to pooling.
    1. If building your grow tray, you will need a drill to create holes for the plant-containing net pots. Holes should be large enough to hold your pots, but small enough that they will not fall through. 
    2. In addition to the holes for your plants, drill one small hole on the top (the same side as the plant holes) of one end of your grow tray and one small hole on the bottom of the other end of your grow tray. Insert the pump tube and the drain tube into these holes, respectively. Use putty or PVC cement to prevent leaking.
  2. Suspend the grow tray(s) above the reservoir. Grow trays should be slanted to allow water to flow from one end to the other, with the end with the hole on top higher than the end with the hole on bottom. There should be no more than a 2% gradient. You can suspend your trays by hanging them or by building a simple frame to hold them above the reservoir. 
  3. Place the water pump in the reservoir, and insert its tube in the hole on the higher end of the grow tray. Insert a shorter tube in the hole on the lower end of the grow tray, and direct it into the reservoir. Allow space between the end of the tube and the water surface in the reservoir to help oxygenate the water.
    1. The water reservoir should be covered to decrease evaporation and prevent sunlight from reaching the nutrient-rich water.
  4. Add your nutrient-rich water to your reservoir. Water volume and nutrient density should be calculated based on the number and type of plants you are feeding.
  5. Turn on your pump to initiate water flow through your system.
  6. Add your plants in their net pots (with a growing medium) to the growing tray, and ensure that their roots are partially submerged in water.
  7. Watch your plants grow!

*Adding an air stone and an air pump to your reservoir will increase the oxygen in the water.  

Deep Water Culture

The DWC system is similar to the Kratky method in principle and set-up, but opts for fully-submerged roots oxygenated via air pump as opposed to roots exposed to air. Like the methods discussed above, the DWC method is best designed for small, fast-growing plants, like leafy greens.

Set-up essentials include everything mentioned above for the Kratky method (the larger-scale one, which uses a five-gallon bucket), plus an air stone, an air pump, and some tubing. 

Steps to prepare your DWC system:

  1. Calculate the amount of water and nutrients needed for your plant(s) based on the needs of the plant(s) you are growing and the volume of water you intend to use.
  2. Make a hole in the bucket lid that is large enough to hold the net pot, but small enough that it will not fall all the way through. The lid can be a normal five-gallon bucket lid if you have the tools necessary to drill a hole into it. Otherwise, styrofoam will suffice.
  3. Place your air stone in the bucket, and connect it with the tubing to the air pump placed on the ground outside of the bucket.
  4. Fill the bucket with nutrient-rich water so that the level will be just above the bottom of the net pot. The pH of your water should fall between 6.0-7.0, but confirm this value for the specific plant(s) you are growing. 
  5. Place your net pot with the growing medium and plant in the hole in your lid, ensuring that the roots are exposed, and turn on your air pump.
  6. Watch your leafy greens flourish!

Hydroponic Nutrients

In addition to light, air, and water, plants require a mixture of nitrogen (N), phosphorus (P), and potassium (K) to grow. These nutrients are delivered in fertilizers, and their respective amounts are quantified using an NPK ratio. The numbers in an NPK ratio refer to each nutrient by percent volume of the total product. For example, a 10-10-10 NPK ratio describes a product that contains 10% nitrogen, 10% phosphorus, and 10% potassium. The ideal NPK ratio for leafy greens in a hydroponic system is 7-9-5. With this information, the amount of fertilizer needed for different plants and systems is still variable and should be researched independently prior to planting.

General Hydroponics, Masterblend, and Foxfarm Nutrients

Popular hydroponic fertilizers include the General Hydroponics FloraSeries® and the FoxFarm Hydro Liquid Trio Pack®—both three-part, hydroponic-specific nutrient delivery systems. The General Hydroponics FloraSeries® consists of three different fertilizers designed for different stages of growth. The first two fertilizers in the series, FloraGro® and FloraMicro®, can be combined in the nutrient-rich water reservoir to favor vegetative growth by pushing nitrogen, calcium, and iron levels up. The last fertilizer in the series, FloraBloom®, is designed to increase phosphorus, potassium, and sulfur levels, encouraging generative growth. Detailed instructions for use can be found online.

Similarly, the FoxFarm Hydro Liquid Trio Pack® consists of three different fertilizers, Big Bloom®, Grow Big® Hydroponic, and Tiger Bloom®, designed to work together to maximize plant productivity by providing ideal nutrient levels. Initially, the first two fertilizers in the series should be combined to promote vegetative growth, followed by the third later on to facilitate generative growth. Detailed instructions and schedules can be found online.

Commonly used as Kratky method nutrients, Masterblend® 4-18-38 Tomato Formula is a completely water-soluble formula that requires mixing with magnesium sulfate (epsom salt) and calcium nitrate prior to utilizing, but requires only one application.

Conclusion

Each of the methods outlined above is beginner-friendly, and presents a path to exciting, quick growth. Regardless of the method you choose to embark upon your hydroponics journey, each offers a promising approach to growing some tasty greens and herbs. 

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