How to use biochar

Biochar needs to be ‘charged’ with nutrients, water and micro-organisms before use. We recommend using one of the following methods for charging biochar (please see the website for more information):

  1. Add biochar to your compost bin/heap. Biochar will add structure to the final compost. It acts as a repository for organic nutrients, water and provides a home for beneficial microbes and fungi. Aim for 10-20% biochar in the final compost. The biochar/compost mix will be ready for use once the composting process is complete.
  2. Fill a large bucket or other vessel with biochar and mix-in compost, well-rotted animal manure and other organic nutrients. Add water until completely immersed. Then leave for two weeks (stirring every few days). 80:20 ratio of compost to biochar is recommended.

Once the biochar is ‘charged’, there are several methods for applying to your soil.

  1. It is best dug-in to the soil for immediate benefits to the soil characteristics.
  2. Alternatively, you can use as a mulch for top-dressing. This is best for trees and shrubs.

Charged biochar is best incorporated with soils from late autumn through to spring and left to settle for a couple of weeks before planting.

We recommend adding 0.6kg of biochar (~30 handfuls) per metre squared per year. If using a charged biochar/compost mix you will need to adjust your calculation based on the ratio between biochar and compost. You are aiming to build-up the amount of biochar in the soil slowly over time, with the long-term aim of getting to ~5% of biochar in the soil rootzone. The rootzone is generally considered to be the top 20 cm of soil. Target 5% built-up over a number of years.

Biochar can be used all year round and with any soil type. It is suitable for trees, flowers, fruit and vegetables.

Instructions for container use

Biochar needs to be ‘charged’ with nutrients, water and micro-organisms before use with pots and containers. See above for more information.

The table below sets out application rate based on an 80:20 compost biochar mix:

Container Size Charged Biochar Compost Application Rate Effective biochar Amount
1 L 25g ~ 1 handfuls 5% 1%
5 L 125g ~ 5 handfuls 5% 1%
10 L 250g ~ 10 handfuls 5% 1%
15 L 375g ~ 15 handfuls 5% 1%
20 L 500g ~ 20 handfuls 5% 1%
25 L 625g ~ 25 handfuls 5% 1%
30 L 750g ~ 30 handfuls 5% 1%

Charging Biochar

This is one recipe for charging biochar, but there are many different ways of doing it. What you are really trying to do, is add nutrients and micro-organisms to the biochar before adding it to your soil. In the video, I have used a mix of compost, animal manure, fish, blood & bone meal to achieve this.

What is biochar?

Biochar grains on the left and under an electron microscope on the right.

Biochar is a black, fine-grained, lightweight and highly porous form of carbon very similar to charcoal. The word biochar is derived from the Greek word bios, “life” and “char”.

Approximately 70 percent of its composition is carbon, which makes it a very pure form of carbon. The remaining percentage consists of nitrogen, hydrogen and oxygen among other elements. The bonds between carbon atoms are very strong  and difficult to break down which means biochar is stable, long-lived and resistant to weathering and decomposition by microbial communities.

Biochar is created by heating biomass to high temperature in a low oxygen environment. This process is called pyrolysis. Almost any biomass can be used but typical feedstocks include wood and plant matter. During pyrolysis the biomass starts to break down at a molecular level and volatile gases are released. These gases are either directly combusted or condensed in a clean and efficient process to generate various forms of energy. Approximately half of the carbon is released during the process; the other half is trapped within the biochar as a stable form of carbon.

Mankind has used biochar for millennia and today it is actively used by farmers in Europe, America and Japan.

Benefits to soil

Biochar enhances overall soil structure enabling plants to develop strong and healthy root systems.

Its highly porous structure acts as a sponge for water and nutrients, providing a home for beneficial microbes and fungi which improve soil fertility and crop yield.

Biochar remains in the essential root area and won’t wash through the soil like other amendments. It resists weathering and decomposition by microbes. Therefore, it is typically a one-time application.

Production of biochar results is carbon sequestration as carbon is locked away in the soil for centuries. This means biochar has the potential to help mitigate global warming and climate change.

Ash which forms part of biochar is alkaline. Therefore, adding biochar can help reduce soil acidity.

Lightweight, stable and long-lasting. Biochar adds bulk to soil and helps improve tilth and aeration. oHigh water-holding capacity. Biochar particularly improves sandy soils that struggle to retain water.

Biochar acts like a sponge absorbing excess nutrients and mitigating soil leaching.