Calculator
Example data table
| Pot volume (L) | Current pH | Target pH | Medium | Lime type | CCE% | Fine% | Method | Estimated lime per pot (g) |
|---|---|---|---|---|---|---|---|---|
| 10 | 5.3 | 6.3 | Peat-based | Dolomitic | 105 | 75 | Incorporate | 40 |
| 5 | 5.8 | 6.2 | Coir-based | Calcitic | 95 | 80 | Top-dress | 20 |
| 25 | 5.0 | 6.5 | Compost-rich | Pelletized | 90 | 60 | Incorporate | 280 |
These examples are illustrative. Your label values can change results.
Formula used
This calculator estimates the product mass needed to raise container pH. It converts pot size into liters, then applies a buffer rate.
Product_g = Pure_g / ECCE
Buffer rates are generalized for common mixes. For precision, use a local buffer pH test.
How to use this calculator
- Choose how you will provide pot volume.
- Enter current and target pH for the crop.
- Select the growing medium that matches your mix.
- Pick a lime product, then confirm label strength.
- Choose application method and optional safety factor.
- Click Calculate to view results.
- Apply lime in stages for changes above 1.0 pH.
- Mix thoroughly to avoid high-pH “hot spots”.
- Water in and recheck pH after stabilization.
Article
1) Why container pH drifts over time
Potting mixes change faster than field soil because the root zone is small and frequently watered. Irrigation alkalinity, fertilizers, and organic decomposition can push pH up or down in weeks. A pH shift of 1.0 is a tenfold change in acidity, so small-looking moves can alter nutrient uptake. Most container crops perform best around pH 5.5–6.5, depending on species and micronutrient sensitivity.
2) Using ΔpH and buffer rate with confidence
The calculator multiplies the pot volume (liters) by the planned pH increase (ΔpH). A buffer rate in g/L/pH represents how strongly the medium resists change. Peat and coir mixes often require fewer grams per liter than mineral-heavy blends. If you are unsure, plan a smaller correction first, then recheck pH after stabilization and repeat if needed. Record your settings so you can repeat successful mixes.
3) Product strength depends on CCE and fineness
Not all lime products react the same. CCE compares neutralizing power to pure calcium carbonate, while fineness reflects how quickly particles dissolve and react. Common labels show CCE values near 90–105%, and fineness can range from 60–90% or higher. Higher ECCE means less product is needed for the same target change in containers.
4) Pot volume is a major driver of dose
Volume determines how much medium must be neutralized. If the pot label is missing, use the built-in shape tools to estimate liters from diameter and height or from box dimensions. For quick checks, 1 L equals 0.264 US gallons. Because volume scales dose directly, a 20 L pot needs about double the lime of a 10 L pot at the same settings.
5) Application method, leaching, and retesting
Incorporating lime evenly into the mix is typically most efficient, while top-dressing can act slower. This tool applies an efficiency factor (for example, 1.00 incorporate, 0.85 slurry, 0.70 top-dress) and an optional leaching factor for heavy runoff conditions. After application, water in thoroughly and retest pH before making another full adjustment. For sensitive crops, split applications across two irrigations.
FAQs
1) Can I use this for lowering pH?
This tool estimates lime for raising pH only. If your target pH is lower than current pH, it returns a zero ΔpH. For lowering pH, consider acid-forming fertilizers or sulfur strategies and confirm with testing.
2) What CCE and fineness should I enter?
Use your product label when possible. If unavailable, start with the preset values. CCE reflects neutralizing power, while fineness reflects reaction speed. Both affect ECCE, which directly changes the recommended grams per pot.
3) Why does top-dressing require more lime?
Top-dressed lime moves downward slowly and may not contact the whole root zone. The calculator reduces efficiency for top-dressing, which increases the recommended product to reach the same effective neutralizing action in the potting mix.
4) How accurate are spoon and cup conversions?
They are approximations based on bulk density, which varies by product and moisture. For better accuracy, weigh a known volume (for example, a tablespoon) once, then use that density value in the calculator.
5) Should I adjust lime for heavy watering?
Frequent leaching can wash alkalinity and dissolved lime through the pot. A small leaching factor (often 5–15%) can help. Increase gradually and retest rather than applying a very large safety factor at once.
6) Is hydrated lime safe for pots?
Hydrated lime reacts very fast and is caustic. It can burn roots and skin if misused. Only use it when you understand the risks, apply carefully, and confirm rates. This calculator requires an acknowledgment to proceed.
7) When should I retest pH after applying lime?
Retest after the medium has had time to react and after a few irrigations. Many growers check within 1–2 weeks for fast products and 2–4 weeks for slower materials, then fine-tune in smaller steps.