The burning question for gardeners

Recent correspondence in The Echo shows that there is still some confusion about the benefits of biochar. I won't go into the wider environmental benefits of sequestering carbon in a long-lasting form, but instead talk about biochar's ability to improve our garden soil.

Call it biochar or charcoal - it's the same thing. Its great feature from a gardener's point of view is that it has a very porous structure on a microscopic scale, with many tiny pits and pockets that can hold onto nutrients and water, as well as providing lodgings for protozoa, fungi and bacteria. These tiny denizens of the soil work in complex ways to create and store nutrients for plants.

It's all about surface area, in essence. The greater the surface area of a given volume of soil, the more potential sites for the storage of nutrients and water. Compost also has a large surface area, and the humic acid it produces works on all soils to improve their structure.

Biochar does not produce humus or humic acid, as it is almost perfectly inert. It can take thousands of years to break down because it isn't acted on by those same soil fungi etc that find it such a hospitable home.

If you want to make your own charcoal you will find instructions on the internet; basically, you need to burn wood in a low-oxygen atmosphere. Do check for fire restrictions and don't set one of these smoky fires where it will annoy neighbours!

If you can't make your own biochar, consider visiting the hardware store and picking up a bag of barbecue charcoal (not briquettes). All charcoal or biochar needs to be ground up as finely as possible before adding it to the soil - a lot of dirty work, so concentrate on making enough for the vegetable garden first.

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