The biochar and compost mix we are giving you, if applied correctly, should not hurt the veggies, flowers, or other plants in your garden. The biochar we are using comes from the Central Valley, is made from 100% wood chips by a company that been making char for over 3 years, and has had it tested at regular intervals. Even if biochar is not produced perfectly (the feedstock is not all completely charred, for example) it is unlikely that it would cause any harm. One study that compared the results from a number of scientific studies showed that 50% showed plant improvement in a biochar-amended plot compared to a control plot, 20% showed no difference, and 30% showed negative results.

Since biochar is generally high in ph (8.5 +), and many plants do better with a ph level in the mid-range, they may not do well with a biochar application unless it is diluted with compost or other nutrients. This is why we are giving participants a measured amount of the biochar/compost mix. It is my guess (it was not noted in the article I read) that most, if not all, of the negative results in the study mentioned  above came from un-inoculated biochar added straight to the soil. If you are interested in looking up specific studies on this subject many are available on the International Biochar Initiative website.

Biochar should ALWAYS be mixed or inoculated with compost, compost tea, or some other source of nitrogen and phosphorus or the biochar will actually compete with plants for these nutrients for up to 6 months. Two companies have received an OMRI rating for their biochar, but much research still needs to be done to satisfy all organic requirements. Since biochar can be made from so many materials, and the characteristics of the biochar in soil can be so different depending on how it was made, a universal organic rating for biochar will never happen—it will likely develop on a case by case basis, just as it is on a farm-by-farm basis.

I would not hesitate to use the biochar we are providing in my organic garden, and I have been gardening without chemicals for over 30 years. As long as you know how and where the biochar was made, and what it was made from, it should be safe to use.

With this being said, all we are asking for in this experiment is for a small 3′ X 6′ section of your garden to test it out—with one control plot and one biochar plot. It will not affect any other areas of your garden. And we want you to use the area with the WORST soil, most likely off to the side of your existing garden area, that has not been amended year after year. This experiment is designed to record any and all effects, both positive and negative, that gardeners experience. So please do report anything, good or bad, that your plants experience under normal conditions.

We are running this study as a way of gaining a better understanding of how biochar use affects plants in Bay Area soils, as most of the field trials thus far have been done in more tropical environments. We expect we will see a great variety of results—from “no perceived difference” to “wow, what a difference,” but we will have to wait to see how the results come in. It is important to know that biochar’s effectiveness at improving soil has been shown to increase over time, so its greatest effects may not surface for several years down the road.

When biochar is produced in a process called pyrolysis, biomass is normally heated from between 450 degrees and 700 degrees C, to a point where the most of the carbon present in the organic matter is made inert and separated from the rest of the chemicals present in the material. This inert carbon (also called recalcitrant organic carbon) is what we call biochar. Most of the rest of the plant material is gasified, and these gases are either recycled back into the pyrolysis process or captured to be burned (like natural gas or biomethane) to produce electricity. Some residual wood oils, called wood vinegar, can also be produced during this process—and this material can be used as a natural insecticide, or even as a salable product (after filtration) as a “Liquid Smoke” product found in the grocery store.

Biochar then, in and of itself, is almost totally free of substances that would be harmful to plants (other than the high ph factor mentioned previously), and in fact creates a coral-like structure that attracts beneficial microorganisms, nutrients, and water. This is why we are so interested in it—it has been proven in test after test to be beneficial to many types of plants. And it only needs to be applied once——since biochar is inert it will not decay for a very long time and will help your plants year after year.

Raymond Baltar
Director
Sonoma Biochar Initiative