Gardening with Biochar

by James Sauer February 16, 2016

I have seen a lot of customer interest in gardening and organic gardening.  It won't be long till spring now that the groundhog did (or did not?) see his shadow. In simple terms, most things grow a lot better and produce better yields after biochar has been introduced. Gardening with biochar involves many variables, but in most cases you can count on observing a noticeable increase in plant growth and harvest yield weights when using fertilizer with biochar, instead of just using fertilizer alone. With some applications the difference can be quite dramatic.

fresh vegetables

Granule size of char:

Depending on what you’ve made your char from, you may need to break it up into smaller granules. From a plant’s roots’ perspective, finer granules are better. However, there is no “rule” to this. After making biochar in your fireplace, you will probably end up with granule sizes ranging from pieces of dust to the size of a pebble. When I remove char from my BioCharlie the charred hardwoods are pretty large but very brittle and easily broken down or crushed. I place them into a large bucket and wet them down to reduce dust.  Just a quick spray with the hose will do it.  I then use a flat blade shovel to chop it up into smaller granules.  This works pretty well for me—but feel free to experiment with different ways.  

Charging your biochar:

A car battery needs to be charged before it can start your car. Biochar is kind of the same way in that it needs to be charged with nutrients before it will help your plants grow.  If you were to add freshly made (uncharged) biochar to your soil it may initially take nutrients away from your plantings, since biochar soaks up the nutrients of its surroundings.  However, this quality is what makes biochar so successful after being introduced to some kind of compost, fertilizer, or nitrogen source first.  I have had success with mixing my biochar into our home’s compost bin for six weeks or longer and then using it in our gardens. You could also charge the biochar faster by mixing it into a compost tea.  No, that doesn’t mean you have to make tea from your compost and drink it or anything!  A compost tea is just a term used for mixing compost with water to make a soupy solution.  Use a large bucket or whatever you have available to do this.  You can also mix in some fertilizer to make it even more potent. Adding the biochar to the tea will kind of “force feed” the char and get it charged up with nutrients in just a day or two.  There are several other ways to charge your char but they are all similar ways of mixing it into various nutrient sources and letting the char take it all in.  You could also charge it as simply as by mixing it into a solution of fertilizer.


Now that you’ve charged up your biochar you can start to introduce it into the soil.  It can be mixed in to the top layer of soil within the root zone of your plants at the time of planting.  Unless you’re trying to do scientific tests for its use I wouldn’t worry about measuring exact amounts or percentages. Just add your biochar-rich compost to your plants the same way you had used plain compost before.  But if you want to do just a little experimentation, try using your char in a few pots or control areas instead of spreading it over the whole garden.  This way you can see what kind of results the char will have in contrast to areas and plantings without it.  Apply or mix some fertilizer into the soil in a normal fashion.


Fertilizer retention:

This is probably the biggest bang for the gardener’s buck!  It may take a couple seasons, but after the biochar has been established in the soil, it will hold on to the nutrients from fertilizers added.  The way fertilizer usually leaches away nutrients in the soil will be inhibited. Biochar will take in the nutrients and make them available for plants year after year.

Microbial activity:

Another fantastic thing about biochar is how it helps the soil come alive with microorganisms. These tiny animals are able to take refuge within the many nooks and crannies of the biochar structure giving them the habitat they need to be healthy and prolific. It is these organisms that make a huge difference in the way nutrients are transported to root structures of plants. With the help of biochar, their increased presence creates a much more fertile soil. But don’t forget the larger organisms in the soil--such as earthworms--that are known to love biochar too!


Breaking up of clay:

We have heavy clayey soil where I live here in western New York. The added biochar helps break up the clay and provides for better drainage and aeration for plants.


Water retention and drought resistance:

Excellent results have been achieved in utilizing biochar in drought prone areas.  Here is a good article talking about its success with California vineyards.   Biochar is like a sponge that readily absorbs water into its cavernous pores.  It is able to retain the water molecules and slow the evaporation process.  Biochar applied to areas that have sandy soils will slow down drainage.  The gardener will appreciate this added drought resistance built in to the soil and not have to water nearly as often after the char has become established.

Water retention

PH Levels:

Another great aspect of using biochar for gardeners is the char’s tendency to raise PH levels of soils: It has a liming effect on soils, increasing alkalinity and making them less acidic.  Aluminum toxicity present in acidic soils is alleviated by the introduction of biochar.

Cation-exchange capacity:

Biochar also increases the soil’s cation-exchange capacity or CEC—that is, a measure of the soil’s fertility.  Technically, CEC is a measurement of the number of positive ions the soil is capable of holding and can make available for exchange with water.

I am not a big gardener myself but my wife loves working on her flower gardens surrounding the house.  To her credit, they do make the place look like a picture from Better Homes and Gardens.  We had used biochar charged with compost for most of our potted plants on our patio last summer and they seemed noticeably more robust, to the point where they were overflowing their pots like they never had in the past.  I plan on doing some side by side tests with potted plants and flowers this coming summer.  We will compare plantings of the exact same plants, soil and fertilizers with and without biochar so we can observe the results side by side at different stages of growth.  I will post our findings and you can then see for yourself.  Others have done similar tests and we expect similar results.

sprouting plants in rich soil

I see lots of value in adding just a little biochar to residential gardens year after year.  It’s a long term investment that will last for many generations to come.  I look forward to seeing the soil improve over the years, even only here around the house, and feeling the accomplishment involved.  I encourage you to do your own experiments with biochar and the plants you like to grow.  I think you will be very pleasantly surprised.




James Sauer
James Sauer


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