Comparing Plants with Biochar Vs Plants Without

by James Sauer August 14, 2016

A picture is said to say a thousand words. There is no exception to this rule when comparing plants grown with biochar next to plants grown without. 

My wife and I have done our own test with some flowers on our back patio, so let's take a look at those first.  In a bit I'll compare and contrast the results of some other field tests to see if we can come to a kind of consensus. 

side by side test

Our test was simple and conducted on our patio where we have grown many of our favorite plants and flowers over the years.  We used our homegrown biochar on some annual plants from the local nursery that were already on their way to maturity and showing blossoms. Both plants were placed in pots that were the same size and shape. The plants we used for the test were purple and peach Verbena and some common red petunias. We planted each with the same type of potting soil, and gave each the same amount of fertilizer and water. 

It has been a rather hot and dry summer here in Western New York so we had to water them just about every day. They were also positioned right next to each other, allowing the same sun exposure. I took the photographs seen above and below one month after the flowers were planted. 

As you can see, the plant on the left is significantly larger and appears more healthy, verdant, and lush. You guessed it! The plant on the left had biochar added to it and the one on the right did not. 

biochar vs no biochar

Both plants were given compost but only the one on the left had biochar mixed in with the compost. As I've explained how to do in a previous post, I charged the char up with the nutrients in the compost before adding it to the pot. On average, various batches of biochar were exposed to the compost for about four to eight weeks time.  The char was mixed into the compost and added to the upper half of the pot only.  I would estimate that the upper half of the pot was15% biochar mixed in with soil and compost.  

The biochar was made using a BioCharlie over the course of several fires in our fireplace. The BioCharlie was loaded most of the time with pieces of mixed hardwoods from our local firewood supplier, but we also used some wood pellets as well (we went with a brand called Nation's Choice purchased from Home Depot). As a side note, we actually found that wood pellets are a nice, easy, and inexpensive way to make biochar.  A forty pound bag was less than $5.00 and you can just poor it into the BioCharlie.  It's easier than splitting firewood into kindling-size pieces, while still using good hardwood feedstock. 

The photographs speak for themselves. We started to note a difference in the growth of the plants just a week or two after planting--the ones with biochar were winning the contest with ease.

It was incredible observing the growth and competition as the days went by. We are planning some other control experiments, but we'd almost rather not plant anything without biochar anymore! 

Please note that the soil with the biochar can and should be used over and over for years with your plantings--the char will actually mature. From the time of its introduction, it will improve the soil for seasons to come. 

So can you yield similar results in your own crops and plants, and help increase their vigor, size and productivity?

Biochar has definitely worked for our plants, but of course there are many factors and variables involved. You may be growing different flowers or plants, planting them in different soils and climates, and making your biochar with different feed stocks. But to show that it could work for you too, I decided to research further to answer this question.  I came across other field studies showing the results for planting with biochar versus planting without.  Take for example this photo taken from a study done at Virginia Tech:

Virginia Tech field study

A paper by Rory O. Maguire, Assistant Professor, Crop and Soil Sciences and Foster A. Agblevor, Biological Systems Engineering at Verginia Tech attempts to answer our question. The paper indicates that most studies show an increase in soil productivity when biochar is added, however, some show decreased productivity. The paper points out that the mixed results are due to the wide variety of biochars as well as that of soils where it is applied. And in turn, as you might have guessed, different plants will also react in different ways to biochar. 

Thus, the paper exercises caution amidst optimism for the use of biochar: "The primary benefits of biochar to soil quality are thought to be through increasing the active surface area that can retain nutrients and increasing the water holding capacity. We need a better understanding of these variables before widely recommending biochar applications to soils".

The paper also notes (as we have before) that use of freshly produced biochars may need several years to retain nutrients and microorganisms before their full benefits to crops may be realized. 

Crop yield comparison with biochar


Quite frankly, it was difficult to locate papers on individual field studies--it is apparent that the number of biochar studies are still relatively scarce. The International Biochar Initiative, however, has a summary of several field studies done over the recent years, Biochar Field Studies: An IBI Research Summary byJosh Laufer and Thayer Tomlinson. One part of the summary highlights the impact of biochar on crop yields, so that's what I'd like to focus on here. The study looks at twenty six field studies done in various locations, soil types, and climates. 

When examining corn yields, the studies show increases of between 20% and 140% above control plots. Just one of the studies showed no significant difference in yield and only one other study showed a decline of corn yield. 

corn with biochar and fertilizer


Rice fields were looked at in several studies. These studies stated that on average, biochar additions to soils did not significantly increase rice yields. However, some field trials showed 12% to 14% increases in yield for unfertilized plots and 8.8% and 12.1% in soils with nitrogen fertilization.  These positive results are significant and beg for the need of additional studies.

Wheat production field tests were also evaluated. A study using a biochar in Western Australia increased yields 18% and up to 46% over the control with a mix of mineral fertilizer. Additionally, authors of one study found positive impacts on germination with applications of biochar due to an increases in early season soil temperatures resulting from the char.

In tests involving soybeans positive results were found.  A large scale study in Quebec had the result of a 20% increase in plant biomass compared with the control plots. Some tests in parts of Europe found mixed results regarding legumes and grapes.


Let's not forget, however, that there are several other benefits to the soil health and the environment from using biochar regardless of its crop yield results.  Taking carbon out of the air and putting it back into the soil is a gift for future generations.  That's what making and using biochar is really about for our generation. 

The takeaway here is that biochar introduction to particular plants or crops needs to be done with small scale tests before rolled out on a large scale. There are so many variables involved that results of using biochar can vary dramatically. If anything, the results highlight the value of field testing biochar as a soil amendment in your own location with your own soil, biochar, and the plants you grow. 



In conclusion--and we have said this before--there still is a lot to learn about biochar. The results we have seen with yield increases so far are very promising. They are encouraging both from a gardening/farming as well as an environmental perspective.

Going forward I will be doing a testing of water retention capacity for biochar.  I will have some plantings in pots with and without biochar.  I will limit the water allowed for the plants in an equal basis and measure the time for wilting to occur.  I may not get to doing this until next growing season but will definitely share my results when they are in. 

Regardless of the yield results, I think we can appreciate how using biochar makes us think about what is going on in the ground and all the interactions between plants, nutrients, and microorganisms. Try using some biochar and see what happens--the mystery and experimentation is part of the fun!  And rest assured that you are doing some good for the planet, as well as your own yard!

Until next time,





James Sauer
James Sauer


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