← Organic fertiliser FAQ

What is organic fertiliser?

Organic fertiliser feeds plants with nutrients held in natural materials, such as plant meals, seaweed and mined minerals, released more gradually than the ready-dissolved salts of a synthetic feed.

The label covers a broad family: single materials like seaweed meal, alfalfa or rock phosphate, and finished blends that draw on quite a few of them. With a natural ingredient, nature sets which nutrients it holds and in what amounts, so no single material is balanced on its own. Blending is how you get round that, combining ingredients so the main nutrients land in the proportions a plant needs, trace elements included.

The word carries two senses. In chemistry, organic means carbon-based: the nutrient is held in a carbon-containing molecule, like the nitrogen in the proteins of a plant meal. A mined mineral such as sulphate of potash is not organic in that strict sense, being a natural mineral salt with no carbon. But because it is mined rather than synthesised, it is permitted in organic growing, so most gardeners still file it under organic.

That difference in form shows up in the ground. Because the nutrient in a carbon-based source is bound into the molecule, soil life has to break it down and free it before roots can take it up, so it feeds more slowly and takes longer to show. In return, that same breakdown feeds the microbes, fungi and worms and builds soil health as it goes. A mined mineral is already in a form roots can take, so it works sooner but does less for the soil itself.