Kratky hydroponics, explained
Kratky Nutrient Solution: How to Mix, Measure and Maintain It
Kratky Nutrient Solution is a plain-English guide to the one thing a Kratky system depends on: the water and nutrients your plants sit in. There are no pumps, air stones or timers in the Kratky method, so the solution you mix on day one has to carry the plant through most of its life. Getting it right is most of the work.
Mixing your first batch? Follow the step-by-step mixing guide
What this site covers
One subject, from the first mix to harvest
I built this site around a single question: what is in the container, and is it still doing its job? Every guide answers one part of that question, and every figure is credited to the university or research source it came from.
Ten guides, in the order you need them From what a nutrient contains to fixing problems before harvest
10 guides
Mixing and measuring
- What a complete hydroponic nutrient contains, and why garden fertilizer is not a substitute
- How to mix a solution from one-part and two-part nutrients
- How strong the solution should be, measured as EC or PPM
Checking and fixing
- Checking and adjusting pH
- When to top up and when to start over with fresh solution
- Reading leaf symptoms that point to a nutrient problem
Why it matters
Why the solution matters more in Kratky
In a Kratky container, the plant drinks the solution down over time. As the level falls, an air gap opens between the lid and the water, and the upper roots use that gap to breathe. Because nothing circulates or refreshes the water, any mistake made at mixing time stays in the container: too weak and the plant runs short before harvest, too strong or at the wrong pH and growth stalls early.
The basics in brief
- Use a nutrient made for hydroponics. It supplies calcium, magnesium and trace elements that soil normally provides.
- Add each part to the water separately. With two-part nutrients, stir part A into the water before adding part B. Never mix the concentrates together.
- Follow the label rate, then measure. An EC or TDS meter tells you the actual strength. Leafy greens generally want a weaker solution than fruiting plants.
- Check pH after mixing. Most crops do well between about 5.5 and 6.5.
- Do not refill to the top once roots have an air gap. Submerging the air roots can drown them. Add a smaller amount instead.
How I approach a new batch
Four checks before a plant goes in
A Kratky container gives you one real chance to get the solution right, so I treat mixing as a short routine rather than a guess. These are the four things I check every time, in this order.
The water
Before any nutrient goes in, I measure the plain water. Tap water already carries minerals, and very hard water can use up a good part of the strength a crop needs before the nutrient is added. Knowing that starting number makes every later reading make sense. The water guide covers tap, well, filtered and rain water.
The nutrient
I only use a nutrient labelled for hydroponics, because a container of water has no soil to fill in the missing calcium, magnesium and trace elements. With a two-part product I stir part A into the full volume of water first, then part B. The choosing a nutrient guide explains how to read the label.
The strength
The label rate is a starting point, not a promise. I check the result with an EC meter, because leafy greens and fruiting plants want quite different strengths and only a reading tells you where you landed. If you see PPM instead, the EC and PPM guide explains why two meters can disagree.
The pH, last
Adding nutrient moves pH, so I adjust it only after the strength is set. A small amount of pH down, a stir, a few minutes and another test is slower than one big pour, but it never overshoots. The pH guide covers strips, drops and meters.
After that, the container mostly looks after itself. The level drops, the air gap grows, and my job is to watch the leaves rather than the water. If a plant turns pale or stops growing, the problems and fixes guide is where I start, and the yellow leaves article helps tell the common causes apart.
Who it is for
Start here
Home growers using jars, buckets or totes, whether you are setting up a first container or trying to work out why a plant has turned pale or stopped growing. Pick the door that fits where you are.
The Blog Single questions answered in depth, each one with its sources listed
Read the Guides Ten guides covering the nutrient solution from start to harvest
Quick Answers (FAQ) Short answers to the questions growers ask most often
Prefer to read one question at a time? The Kratky nutrient solution blog has short articles on single problems, from why pH rises in a Kratky container to how much solution each plant needs.