Watch the free webinar Biochar in Soils, presented by ASLA Oregon in May, 2024

Biochar is a material created when organic matter is “pyrolized” – that is, burned at high heat without oxygen.  The technique (often a byproduct of wild or cooking fires) been used by humans for thousands of years to create fertile soil – in the Amazon basin, it was called “terra preta.”  Because of its chemical structure, it is extremely resistant to decay, and can sequester carbon for thousands of years. It can be created from almost any organic material, in making it a portable and scalable technology. 

For landscape architects, it is most frequently used as a soil amendment, but it can also be used as an additive to concrete to create carbon-negative concrete. (Concrete is typically the most carbon-intensive part of our projects, and worldwide concrete currently creates 8% of emissions, so this is significant). Its environmental benefits include the potential for significant carbon sequestration, diversion of waste stream materials from landfills, and increased plant vitality / less plant loss from lack of water and nutrient-poor soils.  

Biochar in Concrete

Oregon company Solid Carbon has created a performance-neutral, carbon-negative concrete formula that locks up biochar in the concrete, called the Drabkin-Mead formulation. It uses biosolids as the source material, or feedstock, of the biochar. The formula is open-source; you can find specification information on their website: https://www.solid-carbon.com/tech-resources 

Projects that have used biochar concrete in Oregon include the Remy Winery and the Burnside Bridge Skate Park’s 2024 addition. 

The Drabkin-Mead Formulation:  

• CEMENTITIOUS Holcim (Lafarge) OneCem Plus Cement (282 lbs/CY) New Cem Slag (282 lbs/CY)  

• AGGREGATES Windsor Mine (CRH) Coarse Aggregate 4/3 to #4 (934 lbs/CY) Coarse Aggregate 3/8 (585 lbs/CY) Fine Aggregate (1478 lbs/CY)  

• ADMIXTURE Master Builders Pozz 80 (3.00 oz/ cwt) Pollyheed 980 (3.00 oz/ cwt) Glenium 3030 (6.00 oz/ cwt) OTHER WCP, Inc. Batch Plant (A3) WCP, Inc. Batch Water (30 gal/ CY) Solid Carbon Admixture (134 lbc/CY) 

Biochar in Soil

Because of its extremely porous chemical structure, biochar holds water and nutrients and makes them available to plants.  It’s especially beneficial in nutrient-poor urban soils, stormwater planters, and green roofs. In horticultural applications, biochar can replace peat, vermiculite, and perlite.  A typical application can be 5-25% biochar by volume. 

Biochar can be incorporated in both new installations and restoration projects: 

• For ornamental or conventional landscape applications,  when the goal is to improve plant health immediately on installation, you will likely want to incorporate a biochar product that has been co-composted. That is, the supplier mixes the biochar with compost and lets it sit approximately 6 months. Currently (summer 2024), Rexius is the only company that sells co-composted biochar.  Black Owl sells a compost-tea infused biochar online. 

• For restoration applications, when the time horizon for visible improvements is longer, you can mix straight biochar into the soil. It will take several years for the biochar to absorb the nutrients and water in the soil and make them available to plants. 

One of the most common “feedstock” (parent) materials for biochar in the Pacific Northwest is wood. Wood biochar available in PNW (list courtesy of Myles Gray, P.E. from USBI (United States Biochar Initiative):