The Big Biochar Experiment

Sunday, January 20th, 2013
Parsnips with biochar

Parsnips with biochar

Parsnips without biochar

Parsnips without biochar

Just as the papers and magazines periodically come out with a new superfood that will transform your health (acai berries, chai seeds etc etc etc), the gardening world sometimes has its own wonder products. The new kid taking over from mycorrhizal fungi is biochar.


Biochar is similar to charcoal, but is made from burning any and all organic matter (charcoal is made only from wood). The key is the slow burning with very little or no air, a process called pyrolosis. The result is a solid fertiliser product and, as a bonus, the waste gases and liquids can be captured and used as fuels. Not only that, but by making biochar and incorporating it into our gardens, we are locking up carbon in the soil, reducing greenhouse gas emissions. I took part in The Big Biochar Experiment to find out if it was too good to be true.

Like mycorrhizal fungi, biochar is not new, it’s simply been discovered and harnessed for use in horticulture. Thousands of years ago Amazonian Indians were working the forest land with a ‘slash and char’ system, creating incredibly nutrient-rich soils (called terra preta) that persist to this day. In essence, the biochar in the soil forms a sort-of reef within the soil, and nutrients such as nitrogen and phosphorus (essential for good leafy and root growth respectively) and water attach themselves to this structure rather than draining away. Plant roots colonize the ‘reef’ and use everything on it.

Biochar’s other benefits for gardeners are advertised as being able to raise the soil pH, useful if you have very acidic soil, and its nutrient and water retention suggest it might be a viable alternative to peat in potting composts.

It’s still early days, so biochar is still quite expensive, but the early trials look promising. No-one has reported negative results, and consistent results of higher yields, and stronger root development have been recorded. The Big Biochar Experiment sent free bags of biochar to gardeners to trial, an easy way to get a large scale experiment.

I used my bag on my winter veg plot. Having applied the biochar to half the bed (it’s nice stuff to use, you just scatter it over and rake it in to the surface) I sowed/planted out parsnips, chard, kale and sprouts. The first thing I noticed was that the parsnip seeds on the biochar half came up faster and more consistently than those on the control half.

Unfortunately, nasty weather while were away on holiday blew off my netting, and the local pigeons and rabbits had a field day on the kale, chard and sprouts, but the parsnips persisted. Digging them up in January (they were meant for Christmas, but never mind), the biochar roots were not nearly as stunted as the control roots, and much less infected with canker. There were also more of them – you can see the difference in the two photos.

If you want to try biochar for yourself, it’s available as ‘Soil enhancer’ from Oxford Biochar, or in Carbon Gold products. Both are available in some garden centres or online. The Big Biochar Experiment is still running – with free biochar in return for recording your results – give it a go and see for yourself!