← Organic fertiliser FAQ

What is the best source of organic fertiliser?

Your own compost heap, by a distance, because it is free and it is the only source that improves the soil at the same time. Beyond that, well-rotted manure locally, and a bagged blend whose full ingredient list you can read.

Looking for the full answer? See our organic fertiliser FAQ. If you only need one bag, start with All Purpose 4-4-4. To browse the range, open organic fertilisers.

Start with the heap

Nothing you can buy competes with home compost on cost or on soil improvement. It takes kitchen and garden waste you already produce and turns it into the one material a garden always wants more of. Its nutrient analysis is low, well under 1% nitrogen, so it is not a feed in the way a bagged product is, but that is not the job it is doing.

The practical limit is volume and time. Most gardens cannot produce enough compost to feed everything they grow, and a heap takes months. That is the gap the other sources fill.

Where a heap falls short

An ordinary cold heap will not take cooked food, meat or dairy without attracting attention from wildlife, which rules out a good portion of household waste. Fermenting that waste first, in a sealed bucket with a bran activator, is the usual answer: the fermented material can then be buried in a bed or added to the heap, and the liquid it produces dilutes at roughly one part in a hundred as a soil drench.

Well-rotted manure is the other bulk source, and locally it is often free or close to it. It must be well rotted: fresh manure can scorch roots and brings weed seed.

When to buy instead

Buy when you need concentration or precision. Compost cannot deliver 13% nitrogen to a lawn or 50% potash to a fruiting crop, and it cannot correct a specific shortage because you do not know what is in it. A bagged blend can do both, and a single ingredient can do the second exactly.

When you do buy, the test is what the label will show you. Every ingredient named rather than a phrase like "organic base". An analysis that goes beyond three numbers. A rate published for beds and for pots. Those three checks separate most of the market.