Kratky Nutrients: What to Use and How to Mix

In a Kratky system the nutrient solution is mixed once and left to do its job, often for the whole crop. That makes choosing and mixing Kratky nutrients the most important decision after picking the plant.

Why hydroponic nutrients are different

Soil holds a store of minerals and slowly releases them. In hydroponics there is no soil, so everything the plant needs has to be dissolved in the water. A hydroponic nutrient is formulated to supply all of it: the major nutrients nitrogen, phosphorus and potassium; the secondary nutrients calcium, magnesium and sulfur; and trace elements such as iron, manganese, zinc, copper, boron and molybdenum. A general garden fertilizer usually leaves some of these out, because it assumes the soil will provide them. Use a product labeled for hydroponics.

Types of hydroponic nutrient

• One-part powders or liquids. Everything in one product. Simple to measure, which suits small Kratky containers.
• Two-part or three-part systems. The parts are kept separate because some minerals react with each other when concentrated. They give more control over the mix for different growth stages. Each part is added to the water separately, with a stir in between.
• Leafy greens formulas. Some products are made for lettuce and herbs, which need more nitrogen relative to the other nutrients.
• Fruiting formulas. Higher in phosphorus and potassium for flowering and fruit. Better suited to peppers and tomatoes.

For a first Kratky crop of lettuce or herbs, a complete one-part or two-part nutrient made for leafy plants is the easiest place to start.

How to mix nutrient solution

1. Start with clean water. Tap water is usually fine; if yours is very hard or heavily treated, filtered water can give more consistent results.
2. Measure the water volume so you know how much nutrient to add.
3. Add nutrient at the rate on the label for your crop and stage. For multi-part nutrients, add each part separately and stir well between them.
4. Stir thoroughly, then test and adjust pH. See the Kratky pH guide.
5. Pour into the reservoir up to the first fill line described in Kratky kit setup.

How strong should the solution be?

Nutrient strength is measured as electrical conductivity (EC) or as total dissolved solids (TDS, shown in ppm). The label on your nutrient is the best guide, because each product is formulated differently. In general, leafy greens and herbs are grown at lower strengths than fruiting plants, and seedlings at lower strengths than mature plants. An EC or TDS meter lets you confirm that a mix matches what the label intends, and is worth having if you plan to grow more than a jar or two.

For a figure to start from: a University of Florida IFAS Extension guide to the Kratky method (publication HS1488) describes adding nutrient at about 1 teaspoon per gallon of water to reach an EC of roughly 1,250 µS/cm (1.25 mS/cm), or a TDS of about 800 ppm, for leafy crops. A study of Kratky lettuce published in Bragantia used 1.5 mS/cm as the recommended EC for lettuce. Your nutrient label still comes first, because products differ in strength.

Typical Kratky solution strength for leafy greens and herbs

Measure	Typical starting point	Notes
EC	about 1.2 to 1.5 mS/cm (1,200 to 1,500 µS/cm)	UF/IFAS HS1488; Bragantia lettuce study
TDS	about 800 ppm	ppm depends on the meter's scale factor
Dose	about 1 tsp per gallon	for the product in HS1488; follow your own label
Seedlings	lower than for mature plants	many labels give a reduced seedling rate

Because a Kratky solution is not usually replaced, avoid extremes. A solution that is far too weak can leave the plant short of food before harvest. One that is far too strong can burn roots and leaf edges. Following the label for your crop is the safest approach.

What happens to the solution over time

As the plant drinks, the volume falls. The plant also takes up different nutrients at different rates, so the balance slowly shifts. In a short crop such as lettuce this rarely matters. In longer crops, the solution can become unbalanced or run low, which is one reason fruiting plants are harder to grow in small Kratky containers. If a long crop needs more solution, see how often to refill a Kratky kit.

Common nutrient mistakes

• Using plain water. Seedlings may survive for a while on what is stored in the seed, but they cannot grow on water alone.
• Using soil fertilizer. It may lack trace elements, and some organic fertilizers cloud the water and encourage rot.
• Adding "a bit extra". More is not better; over-strong solution can damage roots.
• Mixing concentrates together. Combining parts before diluting can cause minerals to drop out of solution.
• Skipping the pH check. Even a well-mixed nutrient can be hard for plants to use if the pH is far off.

Signs of nutrient trouble

Pale or yellow older leaves often point to a weak solution or a shortage of nitrogen. Brown, crispy leaf edges can mean the solution is too strong. Yellowing between the veins of new leaves is often linked to iron, which can be caused by pH as much as by the nutrient. The Kratky problems and fixes guide goes through these symptoms one at a time.

Go deeper: recipes, measuring and maintaining a solution are covered at Kratky Nutrient Solution, our sister site on mixing nutrient solution for Kratky hydroponics.

Frequently asked questions

Key points

• Use a complete nutrient made for hydroponics.
• Follow the label for your crop and growth stage.
• Add multi-part nutrients separately and stir between them.
• Check pH after mixing.
• Mix carefully at the start, because the batch has to last.

Nutrient choice also depends on what you grow. The best plants for Kratky guide explains which crops are the lightest feeders.