Dial in castings for healthier roots and soil. Choose method, units, and target blend quickly. Get instant ratios, volumes, and download-ready records anytime here.
| Scenario | Total Volume | Castings % | Compost % | Aeration % | Castings Needed | Base Remainder |
|---|---|---|---|---|---|---|
| Container mix | 50 L | 20% | 10% | 25% | 10 L | 45% (22.5 L) |
| Garden bed refresh | 10 ft³ | 10% | 15% | 10% | 1 ft³ | 65% (6.5 ft³) |
| Seed mix | 20 gal | 15% | 10% | 20% | 3 gal | 55% (11 gal) |
| Light top dressing | 100 L | 5% | 0% | 0% | 5 L | 95% (95 L) |
Examples are illustrative. Adjust based on plant needs, drainage, and existing soil conditions.
Worm castings improve nutrient availability and biological activity, but the best proportion depends on drainage and crop sensitivity. For many container blends, 10–25% supports steady growth without making the mix heavy. Seed mixes often perform better with moderate rates because fine media can stay wet longer. For beds, lower percentages can still be effective because the soil profile buffers moisture and salts.
Compost and castings both add organic fines, so pairing them with aeration helps keep pore space open. If compost is included, increase perlite, pumice, bark, or hulls to maintain air-filled porosity. A practical check is the base remainder: if the base fraction becomes too small, the blend may compact over time. Use the calculator to keep totals within 100% while preserving structure.
The ratio tile summarizes how concentrated the amendment is compared with the base component. A 1:4 ratio means one part castings for every four parts base by volume, which is commonly workable for many potted plants. Ratios closer to 1:2 are richer and may require more aeration and careful watering. Ratios beyond 1:1 are typically specialized and should be tested on a small batch first.
Mixing is usually measured by volume, but weight estimates help when buying bagged material or transporting bulk. Bulk density varies with moisture and screening, so the weight output is an approximation. If your castings are very dry and fluffy, use a lower density; if moist and fine, use a higher one. Keeping your own density note improves repeatability across seasons.
Example inputs and outputs (blend mode) for a quick planning check:
Many container mixes work well around 10–25% castings by volume. If the mix stays wet or compacts, reduce castings and raise aeration. Start moderate, then adjust based on watering frequency and root health.
You can, but they behave differently. Castings are typically finer and more biologically active, while compost can add more bulk organic matter. If you increase castings, consider extra aeration to keep the blend open.
The base remainder is what’s left after castings, compost, and aeration percentages. It helps prevent overloading the mix with amendments. A low remainder can indicate a dense blend that may drain poorly over time.
It is an approximation based on bulk density. Moisture, particle size, and packing change density a lot. If you weigh a known volume once, update the density input to match your material for better planning.
A moderate starting point is often around 10–25 g/L, then adjust to plant response. Stronger brews are not always better. Keep aeration, brew time, and cleanliness consistent for repeatable results.
Yes. Seedlings generally prefer lighter, airier media. Use moderate castings, avoid excessive fines, and maintain adequate aeration. If damping-off is a concern, reduce moisture retention and improve airflow and drainage.
Top dressing is useful for established plants when you want gentle feeding without changing the whole media structure. Apply a thin layer and water it in. Mixing is better when you are building a new blend from scratch.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.