Using Biochar in the Garden

Biochar is a stable, carbon-rich material produced by heating organic matter, such as woody debris and other feedstocks in a low-oxygen environment—a process known as pyrolysis. This transformation turns organic materials like wood into a form of charcoal that, when added to soil, helps improve soil health and function.

Historically, ancient civilizations used charcoal to build soil health and fertility. Today, biochar has diverse applications, including agriculture, horticulture, cosmetics, sanitation, medicine, and filtration. 

Benefits of Using Biochar in Your Garden

• Promote healthy root development by improving soil structure and drainage.

• Reduce drought stress by increasing water retention and making water available to plants during dry periods.

• Enhance soil fertility by increasing the nutrient holding capacity of the soil.

• Support beneficial microorganisms by providing habitat for soil microbes that are essential for nutrient cycling and plant health.

• Improve saline or sodic soils by removing salts from the soil solution.

• Mitigate toxins by immobilizing heavy metals and pesticides and preventing plants from absorbing them.

The terms biochar and charcoal are often used interchangeably because they are produced in a similar way and share many characteristics. Both are created by stopping the heating process before the feedstock is fully consumed. However, there are key differences.

Charcoal is primarily used as a fuel for heating and cooking, and today often contains added chemicals (such as those used in grilling charcoal) to facilitate ignition.

Biochar is produced at a slightly lower temperature and is primarily used as a soil amendment to improve soil health and fertility. 

If the feedstock were completely burned, it would turn into ash—the inorganic residue left after full combustion. Ash contains minerals uch as calcium, potassium, and magnesium, which can be beneficial in small quantities. However, ash will not mitigate toxins and does not have the water and nutrient holding capacity of biochar.

Before adding biochar to your garden, it should be “charged” or pre-treated to infuse it with nutrients. This prevents biochar from absorbing nutrients from the soil before the plants can use them. This can be done by:

• Mix with compost or manure – Combine biochar with compost (cured or active), or aged or raw manure to adsorb nutrients and beneficial microorganisms. Start with a rate of 10 to 25% biochar by volume. Use more for compost or manure with a high nitrogen content.

• Soak in nutrient-rich solutions – Soak biochar in compost extract, fish hydrolysate, or seaweed extract for several days to adsorb nutrients before application to the soil. 

  
  

After “charging” the biochar, it can be added to your garden soil at a rate of about 5-25% by volume. For example, in a 100 square foot garden bed a 5% application by volume would be about 2.5 cubic feet or 62.5 pounds.

Spread the biochar evenly and mix it into the top six inches of soil using a shovel or roto-tiller. For no-till systems, top dressing is an alternative, but soil incorporation provides more benefits. Apply biochar during soil preparation, such as before planting in spring or as part of fall soil amendment routines.