Calculator
Example Data Table
These example mixes illustrate typical starting points. Adjust for climate, pot size, and plant needs.
| Use case | Perlite | Soil | Coco | Compost | Bark | Vermiculite |
|---|---|---|---|---|---|---|
| General containers | 30% | 40% | 15% | 10% | 5% | 0% |
| Seed starting | 25% | 25% | 40% | 5% | 0% | 5% |
| Succulents and cacti | 45% | 35% | 5% | 5% | 10% | 0% |
| Moisture-retentive herbs | 20% | 45% | 15% | 15% | 0% | 5% |
Formula Used
- Vliters = Vinput × unit_factor
- Vcomponent = Vtotal × (Pcomponent / 100)
- If base ingredients are normalized: Pi = (100 − Pperlite) × (sharei / Σshares)
- Parts method: Pperlite = partsperlite / (partsperlite + partsbase) × 100
- Optional weight estimate: kg = (L / 1000) × density(kg/m³)
How to Use This Calculator
- Enter the total mix volume and select a unit.
- Select percent-based or parts-based mixing.
- Set the perlite target, then define base ingredients.
- Enable normalization for ratio-style base inputs.
- Press Submit to see the mix plan above the form.
- Use the download buttons to export a CSV or PDF.
Why Perlite Changes Drainage
Perlite is expanded volcanic glass with rigid pores. In container media, those pores raise air space and limit waterlogging after irrigation. As perlite share rises, drainage improves and the wet period shortens, lowering root-rot risk. Very high perlite can reduce water holding, so plants may need more frequent watering and steadier nutrition.
Selecting a Target Percentage
Match perlite percentage to plant demand and pot size. Many foliage plants work well at 20–35% perlite with a balanced base mix. Seed starting often uses 20–30% perlite with more coco or fine peat for even moisture. Cacti, succulents, and shallow bonsai containers may prefer 35–55% perlite to speed drying. Hot, windy sites may need lower perlite to prevent midday wilt. For orchids or aroid mixes, combine higher perlite with bark fines to keep structure, while a small vermiculite share can buffer moisture in tiny pots.
Percent and Parts Outputs
The calculator supports two inputs: a perlite percentage, or a parts ratio such as 1:2. Parts are converted to an equivalent perlite percent, then the base ingredients are split by your shares. If you enable normalization, shares behave like ratios and automatically fill the remainder. If you disable normalization, base percentages must sum to the remaining percent within a small rounding tolerance.
Turning Volumes Into Scoops
Once you know each component volume, translate it into scoops for repeatable batches: scoops = component volume ÷ scoop size. A 10 L mix at 30% perlite needs 3.0 L perlite. With a 0.5 L scoop, that is six scoops. Using one scoop size reduces batch-to-batch variability and speeds mixing on busy planting days.
Planning Weight and Handling
Optional bulk densities estimate carrying weight: kilograms = (liters ÷ 1000) × density. Density changes with moisture and particle size, so treat results as planning values. If you pre-wet coco, compost, or soil, raise densities to reflect added water. For transport, add 10–15% margin for bags, pots, and tools, then record the ratio that drains well.
FAQs
What perlite percentage is a safe starting point?
For general container plants, start around 25–35% perlite. If the mix stays wet for days, increase perlite gradually. If it dries too fast, reduce perlite or increase coco or soil for holding capacity.
Should I rinse or wet perlite before mixing?
Yes. Lightly moisten perlite to reduce dust and help it blend evenly. Rinsing is optional, but dampening improves handling and keeps fine particles from floating during the first watering.
When should I choose parts instead of percentages?
Use parts when you mix by scoops or buckets and prefer simple ratios like 1:1 or 1:2. The calculator converts parts to percent, so outputs still match your total volume target.
Why does the calculator warn about base percentages?
In manual percent mode, base ingredients must add up to the remaining percent after perlite. The check prevents totals above or below 100%, which would distort component volumes and waste material.
How accurate are the weight estimates?
They are rough planning numbers based on bulk density. Moisture, compaction, and product grade change density a lot. Adjust density inputs to match your material, and treat results as a transport estimate.
Can I reuse a perlite-heavy mix next season?
Often yes. Remove old roots, refresh with compost or slow-release nutrients, and check drainage. If particles have broken down or the mix stays soggy, add fresh perlite and bark fines before reusing.