Biochar: A New Trend in Soil Amendment

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Have you heard of biochar? If you’re not a producer of alternative fuels, a climate change researcher, or a student of world food production, it’s unlikely you’ve run into the substance. But that’s all about to change. Slowly, gardeners and farmers are starting to understand that biochar may be the most powerful amendment you can add to your soil to improve its health over the long run. And it does a lot more than just that. Biochar used in agriculture helps sequester carbon, could reduce global warming, and may be one of the keys to sustainably feeding the world.
Here are nine questions and answers about the hottest new development in green gardening:

1. What is biochar?

Hand holding a small chunk of biochar

Biochar is a substance similar to charcoal, but much cleaner. It’s lightweight and porous, with 70% of its composition stable carbon.

2. How is biochar made?

A bucket of biochar

Biochar is made by burning down forestry and agricultural waste (known as “biomass”) in a controlled, low oxygen environment. This process, called “pyrolysis,” produces clean alternative energy while emitting no contaminating fumes. Biochar is its product.

3. So is biochar a recent discovery?

Amazon village

More like a recent “rediscovery.” At the beginning of this century, scientists looking at how to use the remarkable carbon sequestration properties of the biochar, which was a by-product of biomass-based alternative fuels, realized the benefits of biochar as a soil amendment. But adding charcoal-like substances to soil to increase its fertility has been practiced for thousands of years. The most famous example is in the Amazon River basin, where the soil is naturally barren. Two thousand years ago, the indigenous people there were adding burned organic waste to their agricultural fields, creating a much-studied, rich soil, “terra preta,” which to this day puts out record-setting crops.

4. Why is biochar good in gardens?

  • Biochar is extremely porous, and the tiny chambers throughout biochar provide perfect nesting places for the beneficial micro-organisms that support growing plants.
  • Those same chambers also serve as storage areas for water and nutrients, which makes biochar-treated soils drought tolerant.
  • Biochar’s carbon composition attracts important minerals necessary for plant growth, keeping them from leeching from the soil and releasing them when the plant needs them.
  • And finally, biochar makes any toxic, heavy metals in the soil less likely to be taken up by the plants growing there.

5. How does biochar help the environment?

Instead of releasing carbon dioxide, a greenhouse gas, into the environment – the usual result of open burning or decay of agricultural and forest wastes – the process of making biochar “sequesters” the carbon in the biochar itself, allowing it to stay in the ground rather than escape into the atmosphere.

6. How might biochar help world food production?

Parched ground due to drought

Biochar provides a carbon-neutral (and sometimes carbon-negative) soil amendment that can return or bring fertility to famine-prone regions where over-farming or drought has destroyed the soil.

7. How do I use biochar in my garden?

shoveling composted soil from a bin

It is important to note that biochar helps your soil retain and access nutrients and beneficial microorganisms, but it does not contain those important additives itself. Biochar needs to be “charged” by mixing it, at a 50-50 ratio, with high quality compost and letting it sit for at least two weeks before planting in it.
  • You can do this either by mixing a small pile and letting it sit outside through a couple of good rains (or wet the pile).
  • Or, you can add an inch of biochar to your bed then an inch of the good compost on top and let sit in the same conditions.
  • Adding biochar straight to poor soils may lead to the opposite of what you’re hoping for. Without compost to feed on, biochar can end up leeching out the few nutrients left in your beds.

8. Where do I get biochar?

Garden centers and online garden supply outlets are starting to make small amounts of biochar available.

9. Can I make biochar myself?

You can! It’s similar to making charcoal but using a closed environment, such as a steel drum, for the burning. This can be a dangerous activity, however, and may not be appropriate in densely populated or fire-prone areas. If you think you have the space to run a controlled burn, we recommend familiarizing yourself with the process through your local agricultural extension service or other gardening organization.

10. How long does biochar last?

Biochar breaks down slowly compared to fresh organic material. Depending on what it’s made from, biochar can last anywhere from decades to centuries in the environment. With that in mind, a single application is probably all that is needed in your garden to provide benefits for years to come.

The key to getting the most out of biochar is inoculating it with a good quality compost before use. If you’re new to using compost in your garden, check out our beginner’s guide to compost for everything you need to know.


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