Calculator inputs
Example mixes
| Use case | Recipe (percent) | Why it works |
|---|---|---|
| General houseplants | 40% coir · 20% compost · 30% perlite · 10% castings | Balanced moisture and air, with moderate nutrient charge. |
| Seed starting | 55% coir · 30% vermiculite · 15% perlite | Fine texture keeps seeds evenly moist without compacting. |
| Succulents | 25% coir · 15% bark · 35% pumice · 25% sand | High drainage and structure reduces root rot risk. |
Formula used
- Total volume (L): input volume × unit conversion factor.
- Component volume (L): total volume (L) × (component % ÷ 100).
- Component volume (display unit): component volume (L) × liters-to-unit factor.
- Estimated weight (kg): component volume (L) × bulk density (kg/L).
- Estimated cost: component volume (L) × cost per liter.
- Auto-normalize: adjusted % = (entered % ÷ sum of %) × 100.
- Profile scores: weighted average of aeration, water, and nutrients by percent.
- Amendment estimate: (peat+coir liters) × (grams per liter).
How to use this calculator
- Choose whether you’re mixing by total batch volume or by container count.
- Select your volume unit and enter the batch size (or containers + volume).
- Pick components and enter percentages. Keep the total at 100%.
- Optionally edit bulk density and cost per liter for better estimates.
- Enable the amendment estimate and set a grams-per-liter rate if needed.
- Click Calculate mix. Review the breakdown and profile scores.
- Use the download buttons to export CSV or PDF for your records.
Balanced air and water targets
Successful soilless media must balance oxygen and moisture in a container. A practical target for many crops is a medium that drains quickly yet stays evenly damp between irrigations. Coarse particles increase air space but reduce water holding; finer fractions do the opposite. Many ornamentals perform best when the starting pH is roughly 5.5–6.5 and salts are kept modest. Container size, climate, and watering style can shift the ideal balance slightly.
Why percentages matter in batching
This calculator scales recipes from percentages, so the same blend works for a 5‑liter batch or a 200‑liter tote. When your components sum to 100%, each percent converts directly into a measurable volume. If totals drift, Auto-normalize rescales every component proportionally so the finished blend still matches your batch size. This is useful after small tweaks or rounding.
Interpreting bulk density and weight
Bulk density (kg/L) converts volume into estimated weight for transport, storage, and repeatable packing. Light components like coir and perlite reduce compaction risk. Dense ingredients such as sand or compost add stability but can reduce air if overused. Settling after the first thorough wetting is common, especially with fine organics, so plan extra volume for top-offs.
Cost tracking for repeatable recipes
Entering a cost per liter for each component generates a scalable batch cost estimate. This helps compare alternatives objectively, such as perlite versus pumice, or compost versus castings. Export the CSV to track seasonal pricing and to document which mixes deliver the best growth per unit cost. Consistent records make it easier to standardize mixes across sites or staff.
Fine-tuning with amendments and structure
The amendment estimate focuses on peat and coir portions that often benefit from buffering. Use a grams-per-liter rate as a repeatable baseline, then fine-tune based on irrigation water, fertilizer program, and crop sensitivity. If a mix stays too wet, increase structural components and reduce fines. If it dries too fast, raise water-holding components and pre-moisten thoroughly.
FAQs
1) What does “Auto-normalize” change?
It rescales all entered percentages so they sum to 100%. Your relative proportions stay the same, but the calculator adjusts each value to fit the batch volume accurately.
2) Should I measure by volume or weight?
Most growers mix by volume for convenience. Weight estimates are helpful for shipping, repeatability, and detecting moisture changes. Use volume for blending, and weight for documentation and logistics.
3) Are the profile scores lab-accurate?
No. They are practical indicators based on typical material behavior. Use them to compare recipes quickly, then validate with real-world watering performance and plant response.
4) Why does bulk density vary so much?
Moisture content, particle size, compression, and brand differences change density. If you want better weight estimates, fill a container, weigh it, and calculate kg per liter for your material.
5) How can I improve drainage without drying too fast?
Increase aeration with structured components like pumice, perlite, or bark, but also include a moderate water-holding base such as coir or vermiculite. Adjust gradually and retest irrigation frequency.
6) When should I use compost or castings?
Use them when you want more nutrient charge and microbial activity. Keep the percentage moderate for seedlings or salt-sensitive plants, and monitor fertility and moisture because rich components hold water longer.