Biochar is Not New To Food Production But Is Increasingly Being Used To Produce Veg & Fruit. What Is Should We Use It In Garden Soil, Raised Beds & Containers?
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Biochar is one of the components of the manmade highly fertile Terra Preta soils of the Amazon. Though it looks like charcoal there is a huge difference between biochar and charcoal as I will explain in this article where I will delve in to the way biochar is made, how it is different from charcoal and how to use in in garden soils. I’ll also explain the downside of using badly made biochar.
What is Biochar?
Simply put biochar is organic matter such as wood that is burnt in a very low oxygen environment to drive off everything EXCEPT the carbon. That means all the organic matter; oils, tars and related volatile substances; minerals, etc are driven off leaving the carbon skeleton that was once living material. It is made at high temperatures, minimum 500C, * in an oxygen free environment. The high temperature is necessary to allow it to act as a sponge when used to grow plants … more on that later.
Charcoal is also organic material that is burnt in a low oxygen environment. But this is usually at lower temperatures as charcoal is being produced to burn in BBQs etc and the volatile gases etc can be left for burning off whilst the BBQ is heating up. Traditional charcoal manufacture used a pile of stacked wood to be burnt being covered in grass sods to reduce the air flow and this resulted in a lower temperature with less volatile elements being driven off.
Why is this important?
The purpose of biochar is to soak up water and soil microfauna, eg bacteria and fungi, plus nutrients, that the plants can access via their roots as they grow. So driving off everything to leave a carbon “sponge” with billions of holes where the cells structure previously existed is exactly what is required. In charcoal a lot of burnt organic matter and minerals are left behind and that means the carbon “sponge” network is filled with gunk! That means there is less space for all the things that are soaked up by biochar.
So we know that biochar has an extensive carbon network where the cells of the organic matter used to be. Photos of it taken by electron microscopes show how it is like a delicate porous lace network that has a huge surface area. Well, that surface area is negatively charged and attracts and retains positively charged plant nutrients such as potassium, calcium and magnesium. If you are interested in the details of this Google Biochar Cation Exchange Capacity!
Biochar binds nutrients and water molecules tightly enough to prevent them being leached away abut loosely enough for plant roots to access them They do this via Organ-Mineral Interactions such as adsorption and ligand exchange.
Biochar Benefits When Growing Veg & Fruit
Put biochar in your soil and it lasts for hundreds of years. And that is part of the beauty of it. You only need to add it once and it carries on working year after years way beyond your lifetime. But, how doers it help soil?
Soil Structure & Aeration
Biochar helps soil structure and counters soil compaction. Indeed, used correctly, it can make clay soils far lighter and free draining. It does it by altering the density of the soil and by introducing a lot of permanent macropores and micropores which aid soil porosity and overall soil aeration.
In addition biochar soaks up excess nutrients in such a way that they cannot leach BUT can be accessed by plant roots when the plants need them. So in autumn they trap nutrients before the winter rains leach the nutrients away and in spring, as the plants start to grow, make them available to new plant growth.
Microbial activity is higher in soils treated with biochar, retained carbon is much higher and less fertiliser is needed as there is less leaching.
Nutrient Uptake and Growth Acceleration
Biochar mops up excess nutrients, nitrogen, phosphorus and potassium and holds them in the root zone until the plant seeks them when growth demands nutrients. It sounds like magic, but is just simple chemistry and physics in action. Holding nutrients in such an available way in the root zone means Artha then the plant growth starts in spring it is really rapid.
Biochar Increases Crop Yield
Because the plant can readily access nutrients when it needs them this means growth is far more rapid and the plants can generally yield more and much earlier.
For example, in Valencia oranges were given 6 kg of biochar per tree and yield increased 73%. The fruit also showed improvements in juiciness, Vitamin C and sugar content due to enhanced leaf chlorophyl and nutrient uptake.
Research also demonstrated pea yield increases of 69.05% when using conifer biochar and 44.15% yield increase in French beans when using Ash biochar.
Other Biochar Uses
Biochar can also be used to absorb ammonia and nitrogen when added to livestock bedding, as a means to soak up heavy metals in contaminated areas, a means of reducing pollution in water courses and as an additive in concrete to reduce the huge carbon footprint concrete suffers from. It apparently makes concretes, lighter and stronger as well!
Biochar Downsides: Can Biochar Damage Soils?
The answer is NO. But it isn’t quite that easy. Biochar is very good for soils provided it is correctly manufactured and used correctly. That means made from clean “feedstocks” ie wood or other organic matter and made at the right temperature.
But if it is made from recycled construction materials, or similar, that have been painted or treated in some way, OR, if they temperature was too low during manufacture then then the material produced isn’t pure biochar and could easily introduce heavy metals or other pollutants into the soil!
Likewise, if it has been used to soak up pollutants, it should not be added to the soil until it is cleaned … more on how to do that another day!
Clearly we don’t want to added heavy metals to food producing soils. So take care when purchasing or making biochar and ensure it isn’t polluted charcoal.
And on that point, don’t use charcoal as a cheap biochar substitute. Any imported biochar will have had fire suppressant added to it to ensue it don’t catch fire when being transported. To ensure it then burns on our BBQs it is then drenched in petrochemicals to make it combustable. To think we cook food on that! My tip is to buy locally produced charcoal that hasn’t had chemicals added to it.
In my next article I will explain how biochar is made, how to use it in your veg and fruit growing and a few other useful bits.
PS. Biochar needs “charging” before adding to soil or it will adsorb all the nutrients and starve your plants! More on that in the next article.
Research Sources
As regular readers know I always thoroughly research my articles. Below is a selection of biochar research from my local universities. More sources will appear in future articles.
University of Plymouth: Biochar Research
The University of Plymouth conducts high-resolution analysis on biochar through its Biogeochemistry Research Centre and the School of Geography, Earth and Environmental Sciences. Their work frequently intersects with commercial, waste-management, and agricultural entities (such as the Eden Project in Cornwall).
Waste-Derived Manufactured Soils: Plymouth researchers have led critical investigations into how biochar can transform recycled waste or subsoils into high-fertility topsoil alternatives. Studies demonstrated that adding biochar significantly increases carbon (C) and nitrogen (N) retention within manufactured soils, though research notes it acts primarily as a fertility and nutrient-holding booster rather than a direct cushion against extreme climate fluctuations like severe flooding (Rhymes et al., 2024; Schofield et al., 2019).
Green Infrastructure & Living Walls: Recent engineering and environmental applications at Plymouth have tracked how biochar alters the thermal and hydrologic dynamics of urban planting matrices. Trials combining green waste compost with variable biochar fractions (up to 30%) revealed that biochar permanently opens macro-porosity, reducing thermal conductivity at low moisture levels and improving the natural insulation and water-retention metrics of vertical living wall systems (Alencastro et al., 2026).
Microscopy and Feedstock Characterisation: Plymouth utilizes advanced scanning electron microscopy to catalogue individual wood feedstocks (e.g., conifer, ash, oak, willow, hazel). This categorisation helps isolate how specific structural pores alter the soil’s Cation Exchange Capacity (CEC) and provide distinct microscopic habitats for target soil microbes.
University of Exeter: Biochar Research
The University of Exeter approaches biochar from a macro-environmental scale, focusing on climate mitigation models, macro-economics, and geologic carbon sequestration. Much of this research interfaces with the Camborne School of Mines (based at the Penryn Campus in Cornwall) and Exeter’s mathematical modelling groups.
Global Carbon Neutrality Modelling: Exeter researchers have contributed to major international life-cycle assessments evaluating biochar’s scalability. Their published models demonstrate that integrating biomass pyrolysis directly into regional agricultural networks (displacing fossil fuels with the resulting bio-energy while applying the biochar byproduct directly to food crops) can slash systemic greenhouse gas emissions, cut reactive nitrogen runoff by up to 25.5%, and boost absolute crop yields globally (Xia et al., 2023).
Mineral and Geochemical Interactions: Working alongside regional mining legacy data via the Camborne School of Mines, Exeter’s interests overlap with using the structural stability of biochar to remediate complex landscapes, stabilizing heavy metal particulates and identifying organo-mineral relationships in highly weathered or industrialised soils (Schofield et al., 2019).
Biochar’s porous, protective environment acts as a refuge for microorganisms, fostering a beneficial ecological niche that improves soil processes and health. This interaction underpins its growing importance in sustainable agriculture and environmental restoration. I commend the article but it also points out that care must be taken when choosing a biochar source.
Thanks Richard, biochar is a forgotten technique that I believe will be “re-discovered” by many landowners in the next decades. It is important not only when used directly in the soil but also where used as a feed supplement for cattle. Here it reduces methane production and eventually moves into the soil by natural processes.
Biochar’s porous, protective environment acts as a refuge for microorganisms, fostering a beneficial ecological niche that improves soil processes and health. This interaction underpins its growing importance in sustainable agriculture and environmental restoration. I commend the article but it also points out that care must be taken when choosing a biochar source.
Thanks Richard, biochar is a forgotten technique that I believe will be “re-discovered” by many landowners in the next decades. It is important not only when used directly in the soil but also where used as a feed supplement for cattle. Here it reduces methane production and eventually moves into the soil by natural processes.