Why Nutrients Are Split Into A and B
The reason is chemistry, not habit
Solution A contains calcium. Solution B contains sulfate and phosphate. In concentrated form, calcium meets sulfate to become calcium sulfate, and meets phosphate to become calcium phosphate. Both settle out as white lumps that plants cannot absorb.
That is why A and B may only meet after each one has been diluted into the reservoir water. Pouring A and B together into the same container, or mixing the stock solutions first, throws away part of your fertilizer as sediment at the bottom of the tank.
Example Recipe for Leafy Greens
A mix commonly used in commercial greenhouses
| Substance | Stock solution A (kg) | Stock solution B (kg) |
|---|---|---|
| Calcium Nitrate | 9.4 | not used |
| Potassium Nitrate (KNO3) | 3.2 | 3.2 |
| Magnesium Sulfate | not used | 3.2 |
| Mono Potassium Phosphate (MKP) | not used | 3.2 |
| Micronutrient mix | 1 | 1 |
Note that Calcium Nitrate sits only in Tank A, while Magnesium Sulfate and MKP sit only in Tank B. Potassium Nitrate is safe in either one because it does not form a precipitate with calcium.
The figures above are the ones used for lettuce, pak choi, and herbs. After dilution the working strength sits at EC 1.8 to 2.0 mS/cm with a pH of 5.5 to 6.0.
For fruiting crops, the mix changes with the season
| Substance | Dry season (kg) | Rainy season (kg) |
|---|---|---|
| Calcium Nitrate | 36 | 25 |
| High-potassium NPK, for example 11-11-33 plus MgO | 25 | 36 |
| Magnesium Sulfate | 8 | 10 |
| Target pH | 5.8 to 6.2 | 5.8 to 6.2 |
| Target EC (mS/cm) | 2.0 to 2.5 | 2.3 to 2.7 |
The interesting thing about that table is the reversal. In the dry season calcium goes up, because high evaporation makes calcium hard to carry to the end of the fruit and blossom end rot is waiting. In the rainy season potassium goes up instead, because there is less light and the plants need a push so they do not grow too leafy.
If you want to build your own recipe from the single fertilizers sold in Indonesia, single fertilizer blending calculator we work out the grams of each ingredient and show how many ppm of each nutrient element you actually get.
How Many Times to Fertigate in a Day
The number of cycles changes with the crop and the weather
| Crop | Dry season | Rainy season | EC (mS/cm) | pH |
|---|---|---|---|---|
| Lettuce | 9 | 7 | 1.5 | 5.7 to 5.8 |
| Other leafy greens | 8 | 6 | 1.5 | 5.7 to 5.8 |
| Arugula | 4 | 2 | 1.5 | 5.7 to 5.8 |
| Tomato | 12 | 9 | 2.0 | 6.0 |
| Bell pepper | 12 | 9 | 2.0 | 6.0 |
| Eggplant | 12 | 9 | 2.0 | 6.0 |
| Cucumber | 10 | 7 | 1.8 | 6.0 |
The difference between the dry season and the rainy season is not a matter of habit but of evaporation. Hot, dry days make plants give off far more water, so cycles are added. Overcast days keep the growing media wet longer, and adding cycles then leaves the roots short of oxygen.
Start fertigation in the morning once the sun is up, and stop a few hours before dark so the growing media is not wet overnight.
Meters and Calibration
A wrong number is more dangerous than no number
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Calibrate the EC and pH meters every week
Use standard calibration fluids, usually pH 4.01 and 6.86 for the pH meter and 1413 microSiemens for the EC meter. A meter that is never calibrated drifts off slowly without you noticing.
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Check the EC and pH of the flowing solution, not just in the reservoir
What decides things for the plant is the solution that actually reaches the roots. A gap between the reservoir and the end of the hose means there is a blockage or a leak.
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Store the pH probe in storage solution
A probe left to dry out is permanently ruined within days. This is the most expensive damage and the easiest to avoid.
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Write the numbers down every day
A simple note in a notebook is enough. You can only recognize a problem if you have earlier days to compare against.
Questions About This Module
What participants ask most often
Why must solutions A and B never be mixed while concentrated?
Solution A contains calcium, solution B contains sulfate and phosphate. In concentrated form the calcium reacts into calcium sulfate and calcium phosphate, which settle out and cannot be absorbed by the plants.
The result is not just wasted fertilizer. The plants end up short of calcium even though you feel you have given it, and the symptoms show up as blossom end rot or drying leaf edges.
What EC and pH are right for leafy greens and fruiting crops?
Leafy greens such as lettuce and pak choi work at EC 1.5 to 2.0 mS/cm with a pH of 5.5 to 6.0. Fruiting crops such as tomato, bell pepper, and eggplant at EC 2.0 to 2.5 mS/cm with a pH of 5.8 to 6.2.
In the rainy season the EC for fruiting crops is raised a little to 2.3 to 2.7 because there is less light. A pH outside that range locks up some elements so they are not taken up even though there is enough of them in the solution.
Why does the number of fertigation cycles differ between the dry season and the rainy season?
Because evaporation differs. In the dry season plants give off far more water, so fertigation cycles are added to keep the growing media from drying out between them.
In the rainy season the growing media stays wet longer. Adding cycles in that condition leaves the roots short of oxygen and triggers root rot. Lettuce, for example, drops from nine cycles to seven, and tomato from twelve to nine.
How often should EC and pH meters be calibrated?
Once a week for daily use, and more often if the meter is often carried into the field or exposed to high temperatures. Use standard calibration fluid, not plain water.
The pH probe must always be stored in storage solution and never left to dry out. A probe that dries out is permanently ruined within a few days, and that is the most expensive damage that is the easiest to prevent.
Can ordinary NPK be used for hydroponics?
Yes, as one of the ingredients, but not on its own. A compound NPK such as 11-11-33 is indeed used in fruiting crop recipes, but it still has to be completed with Calcium Nitrate and Magnesium Sulfate because ordinary NPK does not carry enough calcium and magnesium.
What often gets missed is the micronutrients. Without iron, manganese, zinc, copper, boron, and molybdenum, plants will show deficiency symptoms even when N, P, and K are plentiful.
All the modules can be read in order or skipped through as needed. See the hydroponics training list, or all training tracks.