Kratky Hydroponics Guides

These Kratky hydroponics guides explain, step by step, how to choose, set up and run a passive Kratky system, whether it came in a boxed kit or you put it together yourself.

The Kratky method is the simplest kind of hydroponics. A plant sits in a net pot above a container of nutrient solution. Its roots grow down into the solution, the plant drinks, and the water level slowly falls. As it falls, the upper roots are left in moist air, where they take in oxygen. There is no pump, no timer and no electricity. That simplicity is why so many beginner kits are built around it, and why it still rewards a little understanding of what is going on inside the container.

Each guide below covers one part of the job. They are written to be read in order the first time, then used as a reference when a question comes up. If you are brand new, start with how the Kratky method works, then read how to set up a Kratky kit before you plant anything.

Who these guides are for

They are written for anyone growing with a Kratky hydroponics kit at home: first-time growers who have just unboxed a countertop kit, people building a system from jars and totes, and gardeners who want fresh herbs and greens through the winter. No experience with hydroponics is assumed.

Start here: the method and the kit

What Is the Kratky Method? The idea behind passive hydroponics, where it came from, and why the falling water level matters more than anything else.
How to Choose a Kratky Kit What separates a useful kit from a pretty box: reservoir size, opacity, net pots, grow media and nutrients.
Kratky Kit Setup From an empty reservoir to planted net pots, including the fill line that most first-time growers get wrong.
Kratky Supplies Checklist Everything a working Kratky system needs, what most kits include, and what you will probably buy separately.

Feeding the plants

Kratky Nutrients Which hydroponic nutrients work in a passive container, how to mix them, and why one batch has to last.
Kratky pH What pH is, the range most crops prefer, and how to test and adjust it without overcorrecting.

The growing environment

Kratky Containers Jars, totes and buckets: how big a container each kind of plant needs and how to keep light out.
Kratky Grow Lights Window light, LED grow lights, hours per day and how far the light should sit above the plants.
Best Plants for Kratky Which crops suit a passive container, which ones struggle, and how to match the plant to the kit.
Kratky Harvest When lettuce, herbs and greens are ready, whole-plant vs cut-and-come-again harvesting, and timing it around the falling water level.

When something goes wrong

Kratky Problems and Fixes Algae, root rot, yellow leaves, leggy seedlings and stalled growth: the usual causes in a Kratky system and what to change. It has its own guides to the four most common problems:

Reference

Kratky Hydroponics Glossary Plain definitions of the terms in kit instructions and guides, from air gap and net pot to EC, TDS and DWC.

How the guides fit together

A Kratky system has only a handful of moving parts, and they depend on each other. The container size decides how long one fill of nutrient solution lasts. The nutrient strength and pH decide whether the plant can use that solution. Light decides how fast the plant grows, and so how fast it drinks. The plant you choose decides how much of everything it needs. When a problem appears, it is usually one of these that is out of balance, which is why the Kratky problems and fixes guide links back to the others.

A few rules hold true across every guide:

Let the water level drop. The space between the lid and the falling solution is where the roots get their air. Refilling to the top drowns those roots.
Keep light out of the solution. An opaque container and a lid with no gaps prevent most algae.
Use a hydroponic nutrient. Plain water or soil fertilizer will not feed a plant that has no soil.
Match the container to the plant. Small herbs and lettuce fit in small containers. Fruiting plants need far more solution.

Guides and the blog

The guides cover the essentials. The Kratky Hydroponics Kit blog goes further into specific situations, such as a DIY Kratky kit vs a boxed kit, choosing between rockwool and clay pebbles, reusing a kit between crops, or running a Kratky kit for kids at home or in a classroom. A good place to begin is the Kratky kit tips checklist, which covers the whole growing cycle in twelve steps.

If you have not picked a kit yet, the home page explains what a Kratky hydroponics kit includes and who it suits.

A note on sources

The Kratky method was developed by Dr. Bernard Kratky at the University of Hawaii, who described it in research papers such as "A suspended pot, non-circulating hydroponic method" (Acta Horticulturae 648, 2004) and a 2009 comparison of three non-circulating methods for lettuce (Acta Horticulturae 843). The guides here explain the same principles for home growers. They do not replace the instructions that come with your kit or your nutrient: when the label and a guide disagree, follow the label for that product.