Kratky Nutrient Solution Basics: What It Contains and Why
In a Kratky container there is no soil to hold nutrients or buffer mistakes. Everything the plant eats comes from the water in the container, so the solution has to be complete from the first day. This guide explains what that means.
What a nutrient solution is
A nutrient solution is water with mineral salts dissolved in it. When the salts dissolve they split into charged particles (ions) that roots can take up directly. In the Kratky method the whole batch is mixed before planting, and the plant draws it down over the life of the crop (Kratky, 2009).
The nutrients plants need
Plants need the same elements whether they grow in soil or water. They are usually grouped by how much the plant uses:
- Primary macronutrients: nitrogen (N), phosphorus (P) and potassium (K). These are the three numbers on a fertilizer label.
- Secondary macronutrients: calcium (Ca), magnesium (Mg) and sulfur (S). Plants use them in large amounts too, but they are often missing from simple fertilizers.
- Micronutrients: iron, manganese, zinc, copper, boron and molybdenum, needed only in small amounts but essential.
Soil supplies some of these on its own. Water does not, so a hydroponic nutrient has to supply all of them.
Why garden fertilizer is not a substitute
Most fertilizers sold for lawns and garden beds assume soil will make up the difference. Many contain little or no calcium, magnesium or micronutrients, and some supply nitrogen in forms that soil microbes convert before plants use them. In a still container of water those gaps show up quickly as pale, stunted or distorted growth. Choose a product labelled for hydroponics and follow its rate for non-circulating systems (UF/IFAS).
Two numbers that describe a solution
- Strength (EC or PPM): how much dissolved fertilizer is in the water. Too weak and the plant runs short; too strong and roots are stressed (Oklahoma State University Extension).
- pH: how acidic the solution is. pH controls whether the nutrients that are present can actually be absorbed.
Getting these two numbers right at mixing time is most of what separates a healthy Kratky crop from a struggling one.
What the solution does not do
A good solution cannot fix poor light, a container that lets light in, or roots kept underwater with no air gap. It is one part of a working setup, alongside the container and the air space that opens as the plant drinks.
Sources
- Kratky, B.A. (2009). Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843: 65–72.
- University of Florida IFAS Extension. Set It and Forget It Hydroponics (HS1488).
- Dunn, B. and Singh, H. Oklahoma State University Extension. Electrical Conductivity and pH Guide for Hydroponics (HLA-6722).
