Mixing Your Own Hydroponic Nutrients

Quick answer

Mixing your own hydroponic nutrients from raw salts costs 70–90% less per liter of working solution than commercial A+B kits and gives you complete control over the formulation. Use two concentrated stock solutions — Stock A (calcium) and Stock B (phosphate, sulfate, micronutrients) — plus a separate calcium nitrate solution if you need more flexibility. Six basic salts cover most crops [OSU-NUT-01].

Why stock solutions

Concentrated hydroponic nutrients require separation by chemistry, not by marketing. Three groups of salts must stay apart at concentration:

• Calcium salts (calcium nitrate)
• Phosphate and sulfate salts (potassium phosphate, magnesium sulfate, potassium sulfate)
• Micronutrients — usually combined with the phosphate/sulfate group

If you concentrate calcium nitrate with magnesium sulfate, you get an instant precipitate of calcium sulfate (gypsum). Combine calcium with phosphate and you get calcium phosphate sludge. Both precipitates are non-recoverable and the resulting "balanced" mix is no longer balanced [OSU-NUT-01].

The standard practice is two concentrated tanks:

• Stock A: Calcium nitrate, often with iron chelate, optionally with potassium nitrate.
• Stock B: Magnesium sulfate, potassium phosphate, potassium sulfate, all other micronutrients [OSU-NUT-01].

Both stocks are dosed at the same ratio (typically 1:1) into the working reservoir, so they only meet at full dilution where precipitation can't occur.

Hoagland-derived formulation

The Hoagland solution, published by Hoagland and Arnon in 1950, is the foundation of most modern hydroponic formulas. A simplified working version for general crops:

This delivers roughly: 200 ppm N, 50 ppm P, 250 ppm K, 200 ppm Ca, 50 ppm Mg, 70 ppm S — a vegetative ratio suitable for tomato and pepper at fruit set [CORN-CEA-01].

For leafy crops, halve the calcium nitrate, halve the potassium phosphate, and target EC 1.0–1.4 instead of 2.0+.

Concentration ratios

Standard practice is 100× stock solutions. To make 100 L of Stock A:

1. Fill a 100 L tank to 80% with warm water.
2. Add 9.45 kg calcium nitrate. Stir until fully dissolved.
3. Add 6.07 kg potassium nitrate. Stir.
4. Add 1.3 kg chelated iron.
5. Top up to 100 L.

To dose: 1 L of Stock A per 100 L of working solution.

Make Stock B at the same concentration, with all phosphate, sulfate, and micronutrient salts. Never combine Stock A and Stock B directly — they meet only in the working reservoir at full dilution [OSU-NUT-01].

Mixing order

When making each stock:

1. Start with water at 25–30 °C (warm water dissolves salts faster).
2. Add the largest-quantity salt first.
3. Stir each addition to full dissolution before adding the next.
4. Add micronutrients and chelates last.
5. Top up to final volume [OSU-NUT-01].

Storage: opaque sealed containers, away from heat and sunlight. Both stocks keep for 6+ months if sealed.

Cost comparison

Per 1000 L of working solution at typical EU/US prices:

• DIY from raw salts: roughly $2–4 in salt cost
• Commercial A+B at hobby pricing: roughly $15–30
• Commercial A+B at bulk pricing: roughly $6–10

The break-even point depends on time cost — mixing stocks takes 30–60 minutes per batch. For growers running over 500 L of working solution per year, DIY pays back the time investment quickly. Below that, commercial A+B is more economical considering labor.

When DIY makes sense

• Commercial operations at any scale
• Researchers running specific formulations or comparisons
• Growers in regions where commercial A+B is expensive or hard to source
• Anyone who wants to control the exact ratio for a specific crop

When it doesn't:

• Hobby growers running under 100 L of solution per year
• Anyone uncomfortable handling concentrated nitrate and phosphate salts (calcium nitrate is hygroscopic and irritating; magnesium sulfate is benign)
• Operations without basic lab equipment (scale accurate to 1 g, EC meter, pH meter) [OSU-NUT-01].

What we recommend

Start with a published formula (Hoagland modified, Cornell CEA, or a university extension publication for your crop) and source food-grade or fertilizer-grade salts from an agricultural supplier. Build the two-stock system, calibrate by mixing a small batch and verifying EC and pH against expected targets, and run the formula on a single test crop before scaling. Once you trust the formula, the cost savings and control are substantial. Don't mix DIY into a commercial A+B reservoir mid-cycle — the trace ingredients differ and you'll get unexpected interactions.