Reference
Biochar in the Garden: What the Research Says
The short answer
Biochar is biomass - wood, corn husks, poultry manure, and the like - heated at high temperatures with little or no oxygen, producing a porous, high-pH, carbon-rich material that breaks down very slowly in soil.
The honest verdict from Extension research is that results on yield are not conclusive: one review MSU cites found about a 10% average yield increase across 16 experiments, but outcomes depend strongly on the biochar's production method and the existing soil, and some soils respond less positively than others. Match it to your soil and expect variability rather than a miracle.
What biochar is
MSU Extension defines biochar as biomass (wood, corn husks, poultry manure, and similar feedstocks) heated at high temperatures in closed containers with little to no oxygen. The result resembles charcoal, with a porous structure, high pH, high carbon content, and a slow decomposition rate.
That slow breakdown is why biochar is studied as a way to build long-lived soil carbon, unlike compost or manure that decompose within a season or two.
Does it improve yields?
The evidence is mixed. MSU Extension notes that results of biochar on yield are not conclusive yet, citing one study that showed a 10% average yield increase across 16 experiments - a modest and variable effect, not a reliable boost.
Soil type matters. Well-drained sandy soils may not gain the moisture-holding benefit as readily as expected, and moderately well-drained or clayey soils may not always respond positively either. The authors emphasize that outcomes depend on both the biochar's production method and the existing soil conditions.
Should you use it?
Biochar is not a plug-and-play fertilizer. Because response varies so much with product and soil, MSU Extension recommends understanding your soil before applying it rather than assuming a benefit.
If you want to experiment, treat it as a long-term soil-building trial on a small area, keep the rest of your fertility program in place, and judge results over more than one season rather than expecting an immediate jump in growth.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Michigan State University Extension - Biochar: An Emerging Soil Amendment — Defines biochar as biomass heated at high temperature with little/no oxygen (porous, high pH, high carbon, slow to decompose), states results on yield are not conclusive (one study showed ~10% average increase across 16 experiments), and notes outcomes depend on production method and soil type, with sandy and clayey soils not always responding positively.