Worm castings: the amendment that outperforms everything else.

Worm castings are the most concentrated soil amendment in organic growing. The numbers are not close. In our two-season trial, castings-amended plots consistently outperformed compost-only, kelp-only, bat guano, rock phosphate, biochar, and fish hydrolysate — not on every individual metric, but as a holistic system assessment that includes plant health, microbial diversity, soil structure, and final harvest quality.

The reason is simple but takes time to understand: worm castings are not a fertilizer. They are a microbial delivery system. A cubic centimetre of quality castings contains approximately 10,000 beneficial bacteria, 1,000 actinomycetes, 200 fungi, and 20 protozoa. When you top-dress with castings, you're not feeding your plant — you're staffing your soil with the organisms that will feed your plant forever.

The practical lesson: apply at a maximum 20% ratio of your total mix volume. More than that and you risk the opposite of what you want — the microbial density becomes competitive and the soil chemistry can become too hot for seedlings. The sweet spot is between 10 and 20% in your mix, topped with a thin casting layer at transplant.

The castings we stock come from a single worm farm in the Loire Valley that has been operating since 2009. The feedstock is exclusively fruit and vegetable pre-waste from restaurant kitchens. No manure. No industrial by-product. The result is a casting so biologically active that we keep them refrigerated in transit.