How the calculator works
The calculator splits the nutrients among the most common water-soluble fertilizer salts, in this order:
- Monopotassium phosphate (0-52-34) supplies all the phosphorus and some potassium.
- Calcium nitrate (15.5-0-0 + 19 % Ca) supplies all the calcium and most of the nitrogen.
- Magnesium sulfate (Epsom salt, 9.9 % Mg) supplies the magnesium and some sulfur.
- Potassium nitrate (13-0-46) tops up the remaining nitrogen.
- Potassium sulfate (0-0-50) tops up the potassium and adds sulfur.
With these five salts you cannot always hit every nutrient exactly at once; sulfur usually ends up a bit high, which does not harm plants. The results table shows what you get compared with what you asked for.
Reference recipes (at 100 %, in mg/L)
| Recipe | N | P | K | Ca | Mg | S |
|---|---|---|---|---|---|---|
| Steiner | 168 | 31 | 273 | 180 | 48 | 112 |
| Hoagland | 210 | 31 | 234 | 200 | 48 | 64 |
How to mix the solution step by step
- Fill the reservoir with water, leaving room to stir.
- Dissolve each fertilizer separately in a bucket of water and add it to the reservoir, stirring well between each one.
- Add the sulfates and phosphate first and the calcium nitrate last, with the reservoir nearly full.
- Add the micronutrients.
- Check the EC and adjust the pH to 5.5–6.5.
If your water is hard (well water high in calcium, magnesium or bicarbonates), a water test lets you subtract what it already contains and save fertilizer. You can do that by editing the target values.
Frequently asked questions
What is the Steiner nutrient solution?
A formula developed by Dutch researcher Abraham Steiner that balances nutrients by their electrical charge: 12 meq/L nitrate, 1 phosphate and 7 sulfate, against 7 potassium, 9 calcium and 4 magnesium. It is one of the most widely used universal recipes for vegetables.
Why do I need two stock tanks (A and B)?
Calcium reacts with sulfates and phosphates when they are concentrated, forming precipitates (gypsum, calcium phosphate) that clog emitters and lock up nutrients. Calcium nitrate goes alone in tank A and the sulfates and phosphates in tank B; they only meet once diluted in the irrigation water.
What strength should I use for lettuce?
Leafy greens are usually grown at 50 to 75 % of the Steiner solution (EC 1.0 to 1.5 mS/cm). Tomatoes, peppers and cucumbers in production tolerate 100 %.
What about micronutrients?
This calculator covers the macronutrients. For iron, manganese, zinc, copper, boron and molybdenum the easiest option is a commercial chelated micronutrient mix at the label rate (usually added to tank B or a third tank).
What pH should a hydroponic nutrient solution have?
Between 5.5 and 6.5. Adjust it at the end, once all the fertilizers are dissolved, using acid (nitric or phosphoric) to lower it or potassium hydroxide to raise it.
Sources
- Penn State Extension — Hydroponic systems: calculating nutrient solution concentrations (Spanish edition)
- University of Almería — Nutrient Solution Calculator (spreadsheet)
- Steiner, A. A. (1984). The universal nutrient solution. Proc. 6th International Congress on Soilless Culture, ISOSC.
- Hoagland, D. R. y Arnon, D. I. (1950). The water-culture method for growing plants without soil. California Agricultural Experiment Station, Circular 347.