Calculator Inputs
Formula used
The calculator builds a recipe in three stages.
- Base recipe: a starting blend by use case and plant focus.
- Adjustments: water and aeration settings shift percentages.
- Normalization: all components are scaled to sum 100%.
How to use this calculator
- Enter the total mix volume you want to prepare.
- Select a use case and plant focus for your crop.
- Set retention and aeration based on your climate.
- Choose a target pH that matches your plants.
- Press calculate and review the blend table.
- Moisten coir, mix thoroughly, then retest pH.
- Download CSV or PDF for repeatable batches.
Why peat substitution is measured by function
Peat’s value is not “peat” itself, but the performance it brings: consistent moisture, stable structure, and predictable pH response. A good substitute blend targets those same functions using renewable or locally available ingredients. This calculator converts your crop needs into a practical recipe, then scales it to your batch volume so results remain repeatable.
Balancing water retention and air space
Most peat-free failures come from extremes: mixes that stay soggy or dry too fast. Coir and compost raise moisture holding, while perlite, bark fines, and rice hulls protect air-filled pore space. The retention and aeration sliders act like quality controls. Aim higher retention for hot, windy sites; aim higher aeration for cool seasons and heavy watering routines.
Nutrient carry and salt sensitivity
Compost contributes biology and nutrients, but it also varies by feedstock and maturity. Too much can push EC, reduce porosity, and create inconsistent growth in seedlings. The nutrient level setting adjusts compost share and shifts volume into structural materials. For propagation, keep compost modest and use controlled fertilization. For mature containers, moderate compost improves buffering and resilience.
pH targets and buffering strategy
Peat mixes typically rely on lime to raise pH, while coir-based mixes may start closer to neutral. The calculator recommends adjustments around your target pH, but it cannot replace testing. Mix a small pilot batch, wet it thoroughly, and check pH after resting. For acid-loving plants, keep pH lower and avoid high-alkalinity irrigation water where possible.
Batching, wetting, and consistency checks
Use volume measures for components, then blend dry and pre-wet slowly to avoid hydrophobic pockets. Squeeze-test a handful: it should clump lightly and crumble, not drip. Example inputs: 40 L total, containers, balanced plants, retention 65, aeration 55, target pH 6.0. Review the blend table, then export CSV/PDF for a mixing sheet.
Example data table
| Scenario | Volume | Use case | Plant focus | Retention | Aeration | Target pH |
|---|---|---|---|---|---|---|
| Balcony herbs | 40 L | Containers | General | 3 | 3 | 6.2 |
| Seed trays | 15 L | Seed starting | Vegetables | 4 | 2 | 6.0 |
| Desert patio cactus | 25 L | Containers | Succulents and cacti | 2 | 5 | 6.5 |
| Blueberries | 60 L | Raised beds | Acid-loving plants | 4 | 3 | 5.5 |
FAQs
Is coco coir always a direct replacement for peat?
Coir can replace much of peat’s structure, but it behaves differently. It wets slower when dry and may hold salts, so rinse and pre-moisten before batching.
Can I skip perlite and still keep the mix airy?
Yes. Rice hulls, bark fines, or pumice can improve air space. The “maximum” sustainability option shifts aeration toward renewable materials where possible.
How accurate is the pH recommendation?
It’s guidance, not a lab test. Compost and bark vary widely by source. Mix your batch, water it, and check pH again before making big amendments.
Why does compost change so much with nutrient level?
Compost drives fertility and microbial activity, but too much can compact or raise salts. The calculator balances compost with structural materials to maintain porosity.
What if I only have leaf mold and garden soil?
Use leaf mold as the organic sponge and add bark or coarse material for structure. Avoid heavy garden soil in containers unless you also add strong aeration components.
Will this work for indoor houseplants?
Yes, especially the container recipe. Increase aeration for plants that dislike wet feet, and aim for steady moisture for tropical foliage by raising retention slightly.
How do I scale the blend for repeated batches?
Keep the same settings, then enter your new total volume. Download the CSV to store your recipe, and label each batch with date and source materials.