Calculator Inputs
Example Data Table
Example recipe for a 20 L batch, aimed at fast drainage.
| Input | Value | Notes |
|---|---|---|
| Total mix volume | 20 L | Use total volume method. |
| Perlite | 40% | Main drainage and aeration driver. |
| Coco coir | 30% | Adds structure and moisture buffer. |
| Compost | 20% | Nutrients and biology for growth. |
| Pine bark | 10% | Improves pore space and longevity. |
Formula Used
- Total volume is taken from your chosen method (Total, Dimensions, or Pots).
- Component volume = Total Volume × (Component % ÷ 100).
- Estimated weight (kg) = Component Volume (m³) × Bulk Density (kg/m³).
- Estimated cost = Component Volume (L) × Cost per Liter.
- Auto-balance scales entered percentages to sum to 100%.
The “Drainage score” is a simple heuristic using the recipe percentages. It helps compare mixes, not replace real-world testing.
How to Use This Calculator
- Pick a volume method and enter the required size or count.
- Choose a preset and click Apply Preset, or enter a custom recipe.
- Keep Auto-balance enabled if your totals are not exactly 100%.
- Optionally enter densities and Cost/L for weight and cost estimates.
- Click Calculate Mix, then download a CSV or PDF for your records.
Tip: If your mix dries too quickly, reduce perlite slightly and increase coir or compost.
Perlite Drainage Mix Guide
1) Why perlite matters for drainage
Perlite is a lightweight, porous volcanic glass that increases air-filled pore space in potting mixes. In this calculator, the perlite percentage directly drives the “drainage score,” helping you compare recipes. Higher perlite usually means faster water movement and less compaction, which is useful for succulents, cacti, and plants prone to root rot.
2) Choosing your target batch size
Accurate volume planning reduces waste and keeps recipes repeatable. Use the Total Volume option for a known batch size (for example, 20 L). Choose Dimensions when filling a raised bed section or planter box, and use Pots when you have multiple containers. The calculator converts all methods into liters for consistent results.
3) Balancing moisture retention and structure
Drainage is only one part of a good growing media. Coir or peat improves moisture buffering, while bark helps maintain long-term structure as mixes age. Compost adds nutrients but can reduce porosity at higher shares. If your pots dry too quickly, reduce perlite slightly and increase coir or bark instead of adding more compost.
4) Estimating weight and handling requirements
The calculator estimates weight using bulk density inputs (kg/m³). This is practical for balcony gardens, rooftop planters, and large container moves. Wet mixes weigh more than dry mixes, so treat results as planning values. If you need tighter accuracy, enter supplier density data for each component.
5) Cost control and repeatable mixing
When you enter Cost/L, the tool estimates per-component and total cost, and exports results to CSV or PDF. This supports consistent purchasing and batch repeatability. Use the parts ratio line as a quick mixing guide: measure the smallest active component as “one part,” then scale the others to match that ratio.
Professional tip: sieve compost and bark fines for more stable drainage.
FAQs
1) What drainage score should I aim for?
Use 55–75 for most container plants, and 70–90 for succulents. It is a comparison aid, not a lab measure. Always confirm with watering behavior and root health.
2) What if my percentages do not total 100%?
If Auto-balance is enabled, the calculator scales your entries so the total becomes 100%. This keeps your recipe proportions consistent without manual rework.
3) Can I mix by “parts” instead of liters?
Yes. After calculating, use the parts ratio line. Pick any measuring scoop as one part, then measure the remaining components in the displayed part proportions.
4) Why does the weight estimate feel low or high?
Bulk density varies widely by brand, moisture, and particle size. Enter your supplier densities for tighter estimates. Wet media can weigh substantially more than dry media.
5) Should I add sand for better drainage?
Coarse grit can help, but fine sand may reduce pore space. If you add sand, use coarse horticultural grit and keep the percentage moderate to avoid compaction.
6) Is compost required in every mix?
No. Compost adds nutrients but can reduce drainage if overused. For sensitive plants, use minimal compost and rely on controlled fertilization for consistent feeding.
7) How do I adjust if the mix dries too fast?
Reduce perlite by 5–10% and increase coir or bark. Also consider a thicker mulch layer and slightly larger containers to improve moisture buffering.