| Use case | Batch | Recipe (by volume) | Notes |
|---|---|---|---|
| All-purpose containers | 20 L | 40% coco/peat, 30% compost, 20% perlite, 10% vermiculite | Good everyday starting point |
| Succulents and cacti | 5 gal | 20% coco/peat, 10% compost, 45% perlite, 10% bark, 15% sand | Fast-draining texture |
| Seed starting | 10 L | 55% coco/peat, 25% perlite, 20% vermiculite | Light and fine |
These are examples, not fixed rules. Adjust to your conditions.
- Component volume: Volumeᵢ = TotalVolume × (Percentᵢ ÷ 100)
- Auto-balance: if percentages don’t sum to 100, each is scaled by 100 ÷ ΣPercent
- Amendment totals: Grams = TotalLiters × Rate(g/L)
- Moisture/Aeration indexes: weighted averages using simple factors per component.
Index factors are approximate and intended for comparison between mixes.
- Select a preset that matches your plant type.
- Enter your total batch size and preferred unit.
- Click “Load preset” if you want fresh preset values.
- Tweak component percentages based on drainage needs.
- Keep auto-balance on to avoid math mistakes.
- Add optional amendment rates if you already use them.
- Press “Calculate recipe” to see volumes and indexes.
- Use CSV or PDF export for shopping and mixing notes.
Volume-first recipes reduce batch variation
Bagged ingredients settle at different rates, so “scoops” drift with every refill. This calculator converts percentages into exact component volumes for any batch size, then shows rounded amounts.
For repeatable results, pre-fluff compressed coir, break clumps, and level your container before each scoop. When scaling up, keep the same percentage profile and only change total volume.
Drainage targets can be set by structure
Air-filled porosity increases as perlite, pumice, bark, or coarse sand rise. A fast-draining mix for succulents often uses 55–70% mineral or chunky media, while leafy ornamentals commonly sit near 25–45% for steadier moisture.
If the aeration index trends low, replace some compost with perlite or bark until roots stay oxygenated after watering.
Moisture retention should match climate and pot choice
Hot patios, terracotta, and small pots dry quickly, so coco/peat and vermiculite help buffer irrigation gaps. Cool rooms and plastic pots hold water longer, so high compost or fine particles may slow drying too much.
A moisture index above 65 often suits plants that dislike drying, while drought-tolerant species commonly perform better below 45. Adjust in 5–10% steps and retest after one cycle.
Amendments work best as rates per liter
Instead of guessing “a handful,” enter grams per liter for slow-release fertilizer, lime, or gypsum. The tool multiplies rate × total liters, keeping nutrient density consistent when scaling from 10 L trials to 80 L seasonal batches.
Many container crops prefer roughly pH 6.0–7.0, but product directions vary. Add gradually, mix thoroughly, and avoid stacking several high-salt inputs in small pots.
Cost and logistics improve with unit awareness
The calculator supports liters, US gallons, and cubic feet for bag comparisons. One US gallon equals 3.785 L, and one cubic foot equals 28.317 L, so pricing can be normalized to cost per liter.
Use the rounding step to match scoop sizes, then export a CSV or PDF as a shopping list. Recording recipes beside plant performance builds a useful library for future seasons.
1) Do the percentages need to equal 100%?
They do if auto-balance is off. With auto-balance on, the calculator scales your entries to 100% while keeping the same ratio between components.
2) Should I measure by weight instead of volume?
Volume is more practical for mixed media because particle size and moisture change density. If you prefer weighing, convert the volumes using your own measured bulk density for each ingredient.
3) What is the moisture and aeration index?
They are simple weighted scores based on typical behavior of each component. Use them to compare mixes consistently, not as laboratory values.
4) How do I choose a batch size?
Start with the total volume needed to fill your containers, plus 5–10% extra for settling. The calculator will scale every component automatically.
5) Can I use sand in indoor potting mixes?
Yes, but use coarse sand sparingly. Fine sand can compact and reduce airflow, especially in small pots. Consider perlite, pumice, or bark if you need more drainage.
6) Are amendment rates universal for all plants?
No. Rates depend on product strength, plant needs, and water quality. Follow label guidance, apply conservatively at first, and adjust based on growth and leaf color over time.