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The 30,000 Year Old Secret To Fertile Soil

Updated: Feb 14, 2022

Wood fire
Biochar has been used in agriculture for over 30,000 years.

Biochar is a type of charcoal found in soils around the world as a result of vegetation fires and historic soil management practices that have been used for over thousands of years. Almost since humans have roamed the earth -- for 30,000 years or more -- we have been using slash and burn techniques to improve crop productivity.

Soil scientists have been studying this ancient form of agriculture for quite a while, and have found that biochar can be a hugely beneficial soil amendment for almost any type of residential or commercial landscape, especially vegetable gardens.

Benefits Abound

Here's what adding biochar to your soil can do for you:

  • Reduce water needs

  • Aerate soils and reduce compaction

  • Reduce fertilizer and chemical inputs

  • Optimize pH

  • Increase nutrient uptake

  • Encourages bio diversity and microbe activity

  • Sustainable, natural, and safe

  • Biochar lasts at least ten times longer than compost

So what is biochar? And how can you use it in your landscape?

Hand holding biochar
Biochar is created by burning wood in a low-oxygen environment. The resulting charcoal is a lightweight and highly porous.

How Biochar Is Made

Biochar is made by burning wood and other plant materials in a low-oxygen environment.

An early example of using biochar as a soil amendment comes from the Amazonian Indians, known as Terra Preta. The Amazonians added a lot of other materials to their charcoal, such as pottery shards, bones, and fish heads.

An example of using pure biochar comes from the "Forest Finns" of Norway and Sweden, who put their own twist on this ancient technique. First they would girdle trees within a tract of land. Girdling strips off the bark from around the trunk of the tree, which quickly kills the tree. The following year, they would burn the dead, dry trees to the ground. As soon as the ground had cooled, they would sow rye. They then fertilized the rye by allowing their livestock to graze on the rye seedlings and leaving their manure behind.

During the second year, they would fence off the rye crop. Rye is not only a great food source, but it is also a "cover" crop, which means that, as it grows, it restores nitrogen to the soil by pulling this key nutrient from the air.

Over the next two to three years, they could plant more rye or other food crops. The resulting harvests yielded 10 to 50 times as much as ordinary farming methods.

Modern Methods

Luckily, you don't have to kill your trees, shatter your pottery, or wait three years to reap the benefits of biochar. Today it is commercially available and made from recycling yard waste and other sustainably-sourced ingredients.

barbecue, charcoal briquettes, BBQ
Charcoal for barbecuing is not "activated" and burns much hotter and more quickly than biochar.

The terms biochar and charcoal are used interchangeably. And the charcoal used to barbecue your steaks is very similar to biochar. In modern commercial processing, both biochar and charcoal briquettes are made by burning wood in large concrete or steel silos to create a low oxygen environment. The lack of oxygen prevents the fire from reducing everything to ash. The process can take several days and burns off volatile compounds such as water, methane, hydrogen, and tar. The process leaves black lumps and powder, about 25% of the original weight.

"Activated" Vs. Non-Activated

The difference is that, with biochar, more oxygen is used to increase the porosity and surface area of the chunks. When charcoal briquettes are ignited, the carbon in the charcoal combines with oxygen and forms carbon dioxide, carbon monoxide, water, other gases, and significant quantities of heat energy. It packs more potential energy per ounce than raw wood.

Biochar, on the other hand, burns more steadily and produces less smoke and fewer dangerous vapors. The result is that, unlike charcoal briquettes, biochar still helps provide nutrients for soil microbes. For that reason it is often referred to as "activated charcoal." Another difference is that because it is activated, biochar absorbs volatile gases -- it's often used to soak up odors and bind with impurities, leaving the beneficial ones like oxygen behind.

Lasts 10 Times Longer Than Compost

Cultivation necessarily depletes the soil by converting natural materials such as leaf litter and fallen fruits into plant food. Chemically-based agriculture depletes soil carbon more drastically. High nitrogen fertilizers combined with tillage accelerate microbial respiration, burning up soil carbon faster than it can be replaced. Due to this rapid loss of organic reservoirs, soils eventually become lifeless substrates that must be continually irrigated, fed with mineral nutrients and sprayed with pesticides to produce a crop.

Even most organic gardeners usually remove leaf litter and other debris from our lawns and beds, which means that we still need to replenish our lawns and beds each season with fresh compost and periodically feed our plants with fertilizers. We just don't need to use as much.

Hands holding compost
Compost and biochar work together to replenish the nutrients in your soil.

Compost is quickly broken down by microbial action in soil over a period of months, depending on climate. Biochar lasts at least ten times longer! The two work extremely well together to make a "super food" for you soil microbes. Since it is lightweight and absorbent, it is also an excellent amendment for breaking up heavy soils or adding density to loose, sandy ones. And unlike expanded shale, which needs to be worked into the soil, biochar can be used as a top dressing.

Choosing the Right Product

One concern about using biochar is it's consistency. There are many different methods for producing it and many variations in the level of activation, and therefore, the quality of the charcoal. Different grades are also available for different uses -- for example, cosmetic grade is different from agricultural grade. So it's important to get one that's right for your garden.

We've recently added CarbonizPN Soil Enhancer by Mirimichi Green, a professional blend of premium organics and USDA-certified plant-based carbon. CarbonizPN can be used any where in your garden, including on new and existing turf, around your trees and shrubs, in your flowerbeds, or as a topdressing. If you are planning to install new sod, apply a layer of CarbonizPN underneath it first for better results.

Mirimichi CarbonizPN comes in a 40lb bag. (Check with us for current pricing.)

Here's a quick guide to how much you'll need:

Turf and Lawns

Apply 20 to 80 lbs per 1,000 sq. ft.

Plants and Flowers

Incorporate 2% to 10% by volume into planting mix or soil


Apply 2 to 10 lbs per caliper inch around the base of the tree

Soil Conditioning For Existing Soils

Incorporate 40 to 110 lbs per 1,000 sq. ft. into top 3-6 inches of soil

You'll find biochar in our organic products department.

Links: Nerdy scientific articles about biochar:


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