There’s a substance that Amazonian civilisations were using to build soil two thousand years ago, that modern research has confirmed does exactly what they seemed to know it would, and that you can buy on Amazon right now for about $22 a bag (£18). It’s called biochar. And despite the fact that it genuinely works, most of the conversation around it is either overblown or buried in academic papers that nobody reads.

Let me show you what the numbers actually say.

What It Is

Biochar is charcoal — specifically, charcoal produced by heating organic material in a low-oxygen environment, a process called pyrolysis. The key difference between biochar and the charcoal you put in a barbecue is the feedstock and the temperature. Good biochar is made from clean organic material at temperatures above 400°C. What you get is a highly porous carbon structure that is, for most practical purposes, permanent.

That last point matters. When you add compost to soil, the carbon in it cycles back out into the atmosphere within a few years. When you add biochar, the carbon stays put. This is why it attracts attention from people interested in carbon sequestration. But the soil benefits are the more immediately useful story.

What It Does

The porous structure of biochar creates an enormous surface area — a single gram can have the surface area of several tennis courts. In soil, this does a few things:

It holds water. Sandy soils that drain too fast retain more moisture when biochar is present. Studies from the University of Edinburgh found water retention improvements of 15–20% in sandy loam soils — meaningful if you’re farming in a dry summer.

It holds nutrients. The same porous structure that holds water also retains ammonium and other nutrients that would otherwise leach away. This means less fertiliser washes into waterways, and more of it stays available to plants.

It supports microbial life. Biochar creates habitat. The pores become home to the bacteria and fungi that healthy soil depends on. This isn’t mystical — it’s the same reason old-growth forest soils are so productive. Structure matters.

What it doesn’t do is fertilise directly. Biochar has very little nutritional value on its own. The confusion here has caused some disappointment — people buy it expecting a fertiliser and wonder why nothing happens. It’s infrastructure, not food.

The Numbers on Carbon

A tonne of biochar contains roughly 0.8–0.9 tonnes of carbon, depending on feedstock and production temperature. That carbon came from atmospheric CO₂ via the plant material used to make it, and it will stay in the soil for centuries rather than cycling back out quickly.

The carbon accounting gets complicated when you factor in the energy used in production, but high-quality pyrolysis systems designed for biochar production — not waste incineration — can achieve net negative carbon figures of 0.7–1.1 tonnes of CO₂ equivalent removed per tonne of biochar produced. That’s meaningful at scale. It’s not a silver bullet, but it’s real.

The Suppliers Worth Knowing

Not all biochar is equal. Temperature, feedstock, and production process all affect quality. Here’s who’s doing it properly.

Where It Makes Sense

Biochar makes the most sense in one of three situations: degraded soils with poor structure, sandy soils with drainage problems, or intensive agricultural systems where nutrient retention has real economic value.

It makes less sense as a short-term fix for fertile soil that already has good organic matter. You’re not going to see dramatic results in a well-managed garden bed. The effect is cumulative and structural.

The economics for small-scale use are marginal. At current prices, you’re paying roughly $100–130/tonne (£80–100) for commercial products, and you need to apply it at meaningful rates — 5–10 tonnes per hectare for agricultural use — to see significant benefit. That’s a substantial upfront cost with long-term payback.

Right Then

Here’s what the numbers actually say.

If you’re a home gardener: biochar is a soil intervention, not a return on investment. At $22 a bag (£18), it’s a reasonable addition to sandy or depleted soil if you treat it as infrastructure — something that improves moisture retention and microbial habitat over years, not seasons. Don’t expect to see it in your harvest figures.

If you’re farming at scale: the economics shift. A 10-tonne-per-hectare application runs roughly $1,000–1,300 (£800–1,000) per hectare at current commercial prices. Against meaningful yield improvements in degraded or sandy soil, that can make sense over a five-to-ten year horizon.

Carbon credits are real, but they’re not for individuals. The voluntary carbon market — platforms like Puro.earth — does issue Biochar Carbon Removal credits, currently trading around $150–165 per tonne of CO₂ equivalent. But certification requires a minimum of roughly 500 tonnes of biochar per year and upfront costs of €18,000–55,000. This is infrastructure for commercial producers, not income for smallholders.

The thing that gets me about this is that it’s been sitting there, under Amazonian rainforests, as evidence, for two thousand years. We just weren’t looking.